REVERSION IN GUINEA-PIGS AND ITS EXPLANATION

By yV. E. CASTLE

EXPERIMENTAL STUDIES OF THE INHERITANCE

OF COLOR IN MICE

By C. C. little

WASHINGTON, D. C.
Published by the Carnegie Institution of Washington

1913

^ (1,0

Carnegie Institution of Washington. Publication No. 179.

Papers Nos. 18 and 19 of the Station for Experimental Evolution at Cold Spring

Harbor, New York.

2 ^f 7 /

Copies of this Bool*
were first issued

SEP 13 1913

PRESS OF GIBSON BROTHERS
WASHINGTON, D. C.

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

By W. E. CASTLE.

Professor of Zoology in Harvard Ihrivcrsiti/,
Research Associate of the Carnegie Institution of Washington.

Paper No. 18, Station for Experimental Evolution at Cold Spring Harbor, New York.

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

In 1905 I showed that when black-coated guinea-pigs of pure race are
mated with red-coated ones only black-coated young are ordinarily produced,
and that if such young are in turn mated with reds, both black young and red
ones are obtained. In other words, black is a mendelian dominant to red.
The fact was, however, noted that occasionally the cross of black with red
causes reversion to the agouti or wild type. But this may be regarded as a
modified condition of black, since the hairs of the agouti animal contain black
pigment, but disposed in a definite pattern with red, the entire hair being black
except a terminal or subterminal band of red (or yellow).

An examination of the tables of matings published at that time shows that
all the agouti animals so produced were the progeny of a single red animal,
6^2054. This animal produced black young as well as agouti ones in crosses
with black, so it was not clear to what the reversion was due. By a study of
the progeny of this animal the matter was later cleared up. The black young
were found never to produce agouti young in crosses with any red animals
unless such reds were descended from 6^2054. The agoutis, however, produced
a mixture of agoutis, blacks, and reds, when mated with ordinary red animals.

These and other corroborating experiments, reported briefly in 1907,
showed that the agouti reversion in crosses of black with red is due to a factor
transmitted by the red parent, never by the black one. For, as I then showed :
(1) a red animal which produces the reversion to agouti in crosses with one
black animal will produce it in crosses with any black animal ; but (2) no black
animal will produce agouti young unless crossed with a red animal which also
produces agouti young in crosses with other black animals.

For simplicity, the something possessed by red animals which induces
reversion, I have called the agouti or A factor. It is invisible in the red animal,
since the hairs of such animals are red throughout their length. Its only dis-
coverable function is to exclude black from the terminal portion of the hair,
and this function plainly can not be exercised unless black pigment is present.
Now this agouti factor is transmitted like any other simple independent men-
delian factor. Some reds are homozygous in A and so transmit it in all their
gametes. A very fine female of this sort, kindly loaned me in the summer of
1906 by Mr. B. B. Horton, was mated with two different black males (cr4456
and cf 9538), by each of which she bore five young, all agouti-marked. These
same males when mated to other red females produced only black young.

Most of the agouti-producing reds which I have had, including the original
cf 2054 (received in June, 1903) and some of his descendants, have been hetero-
zygous in the agouti factor, so that when mated with black animals they pro-
duced in approximately equal numbers agouti 3'oung and black ones. All

3

4 REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

reds which I have had, derived from other sources than these two, have failed
to produce agouti young in crosses with black animals; see the summary in
table 1, p. 8. They may therefore be considered to lack altogether the agouti
factor in which wild species of cavy are regularly homozygous.

The agouti factor is transmitted through albinos exactly as are other color
factors. Accordingly an albino may or may not possess and transmit the
agouti factor; if it does possess this factor, it will produce agouti offspring
when crossed with a black animal. Several examples of this have been ob-
served among the albino descendants of cf 2054. Thus red cf 3496, table 1,
which when mated with heterozygous black females produced red young and
black ones but no agoutis, Avhen later mated with the albino females 4270 and
4262 produced 4 red and 4 agouti young. The father of these albinos, it should
be said, was an agouti animal.

Agouti animals produced by crossing black with red do not breed true.
They produce three classes of young if bred with each other or with ordinary
reds. The latter form of test has been more commonly employed in my experi-
ments because I had more red animals than agoutis and it was easier to ascer-
tain their gametic composition. Fourteen young, however, were obtained from
the mating of Fi agoutis inter se; they were 2 red, 2 black, and 10 agouti; see
table 2, p. 9. The mating with reds produced 111 red, 45 black, and 40 agouti ;
expected, 98 : 49 : 49. This expectation is calculated as follows: It is expected
that half the young will be red because the agouti parent is known to be hetero-
zygous for red. It is also expected that half the young will receive the agouti
character, which those possessing black pigment will show, but which those
possessing only red pigment will not show. Hence all the reds should look
alike, but half the others should be agouti. In the mating inter se of agoutis
of this generation the expectation is 4 red : 3 black : 9 agouti ; the observed
numbers, as stated, are 2 : 2 : 10, in a slightly smaller total, 14. The tests
summarized above relate to five different Fi reversionary agouti males. Three
of them were descendants of my original red male, 2054; the other two (9150
and 9152) were sons of Horton's red female. All gave similar results.

Agouti young produced by the mating already described of an Fi rever-
sionary agouti with an ordinary red produced the same kinds of young as did
the Fi agoutis, viz, red, black, and agouti; see the second division of table 2.
The tests applied in this case were identical in character with those applied to
the previous generation, viz, matings inter se and with ordinary reds (lacking
A). Twenty-four different male animals were tested in one or both of these
ways, while several females were tested in the first-mentioned way. The data
for these are recorded for convenience in connection with the male involved in
the same experiment. Only two of the various animals tested failed to pro-
duce all three classes of young. In the case of these two, 9602 and 9685, there
can be little doubt that a more extended test would have produced the missing
class. Male 9602 produced 2 black young and 1 agouti. A further test would
almost certainly have given red young, since his mother was red. Male 9685
produced 4 red young and 2 black ones. That he could also have produced

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION. 5

agouti young can scarcely be questioned, since he was himself an agouti. The
total progeny of the 24 males by red females is 133 red, 66 black, and 69 agouti,
the expectation being 134 : 67 : 67. By agouti mates they produced 25 red,
21 black, and 63 agouti young, the expectation being 27 : 21 : 61. These are
remarkably close agreements. One of the 24 males, 7932, was also mated
with a black female, producing 2 black and 2 agouti young, the expected
equality ; no red young were to be expected.

Agouti animals produced by mating agouti animals inter se are not so
uniform in behavior as those thus far discussed. Experiment shows that they
fall into four groups:

I. Agoutis producing red, black, and agouti young.
II. Agoutis producing only red and agouti young.

III. Agoutis producing only black young and agouti young.

IV. Agoutis producing only agouti young.

Group I is represented by nine agouti males, whose parents were both
agoutis; they were enumerated in the third division of table 2. Together they
have produced (a) by red mates, 34 red, 20 black, and 19 agouti young ; expected
36 : 18 : 18; (6) by agouti mates, 3 red, 5 black, and 14 agouti young; expected
5 : 4 : 12, if the females were of the same character as the males, as most of
them doubtless were; (c) by black mates, 3 black and 3 agouti young, the ex-
pected equality, no reds being expected.

Group II is represented by the ten animals enumerated in table 3. They
proved to be incapable of producing black young in any sort of mating. Mani-
festly they were homogyzous in agouti. By red mates they produced 53 red
and 52 agouti young. They were accordingly heterozygous in red, and equality
of red and agouti young was to be expected. By agouti mates they produced
13 red and 62 agouti young. The expectation in this case varies with the
character of the agouti mate employed, which was not in every case definitely
determined. If the agouti mate belongs in Group I or II, then the expec-
tation is 1 red : 3 agouti; but if the mate belongs in Group III or IV, the
expectation is all agouti young. If the mates are a mixture of the two sorts,
as a random group of F2 agoutis should be, then the expectation lies between
75 and 100 per cent agoutis; the percentage obtained is 82.66. By black
mates, the Group II agoutis produced 18 young, all agouti, as expected. These
were sired by two animals, both of which by red mates had produced red
young as well as agouti young.

Group III is represented by the 16 tested animals enumerated in table 4.
They were incapable of producing red young, and hence were homozygous in
black. But since they produced black young as well as agouti, it is evident
that they were not homozygous in agouti. Three females (374,437, and 462)
are included only provisionally in this group, since they were not tested by
matings with red animals, but only with black ones. They are known to have
produced black young, but it is not certain that they could not also have pro-
duced red young, in which case they would fall in Group I. The test in the
case of several other animals (as 5, 68, and 314) rests upon too small numbers

6 REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

to be conclusive, but suffices to show that the animals in question were not in
all reSj^ects homozygous, the condition it was desired to obtain in the experi-
ment These animals were therefore promptly discarded as soon as evidence
was obtained that they produced other than agouti young. In the case of
animals 191, 6197, 7894, 8020, and 9939, the numbers of young are sufficiently'
large to establish beyond question their position in Group III.

The animals included in table 4 together have produced by red mates 51
black and 91 agouti young. If all the red mates used lacked the agouti factor,
we should expect equality of black and agouti young; but from this expecta-
tion we observe a considerable divergence. It is quite possible that in some
of these tests red animals were used which were descended from cf 2054 and
had inherited from him an unseen agouti factor, for in making the later tests
some such animals were emplo3^ed, but it is doubtful whether this accounts
for the whole discrepancy, amounting to about 14 per cent. This doubt is
strengthened by the similar discrepancy observed in the tests with black mates,
where we expect equality of black and agouti, but obtain 5 and 12 respectively.
The case of animal 191 looks suspicious; he produced only one black young one
in a total of 22, yet the record is certainly accurate. We had provisionally pro-
nounced him a pure agouti, when the single black young one came which places
him in Group III. It seems doubtful whether the theoretical 50 per cent of
his gametes were entirely free from the agouti character. If so, such gametes
would seem to have been deficient in vitality. The deviation is, however, not
an impossible chance result, though it seems improbable. I regret that this
animal was not more extensively tested. The matings of animals of Group
III with other agouti animals produced 9 black and 46 agouti young, or 84 per
cent agouti, where we expect between 75 and 100 per cent.

Agouti animals of Group IV are included in table 5. They represent the
"fully fixed" agouti type breeding exactly like a pure wild species as regards
color. Two thoroughly tested animals belong here beyond question, cf^l45
and cf 316; two others less fully tested belong here in all probability, viz, cT 160
and 6^181, while 9 473 is included as a possibly pure animal. She was fully
tested qualitatively (by a mating with a brown-eyed yellow animal known to
lack both black and agouti), but the number of young obtained is not large
enough to make the test conclusive. Similar tests of other females might be
included in the table, but they would add nothing to the demonstrative case
of cfl45, which shows that the reversionary character obtained by crossing
can be obtained in a homozygous, pure condition, as it occurs in wild species.
The five animals enumerated in table 5 have produced only agouti young : (a)
by red mates, 52; (6) by agouti mates, 135; (c) by black mates, 26.

The occurrence of four different types of F2 agoutis indicates that the Fi
agoutis, their parents, were heterozygous as regards two independent mendelian
unit-characters, in agreement with the interpretation already given. These
two characters are: (1) black-pigmented fur; (2) the agouti pattern (visible
only in black-pigmented animals). Designating these two units as B and A
respectively, the Fi agoutis are all of the formula AB (heterozygous in both

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

units). Their gametes are il 5, ^, 5, 0. If an animal producing such gametes
is mated with a red animal lacking both units, the zygotes formed wojld be,
as regards these units, AB, A, B, and 0, or agouti, red, black and red respec-
tively, or collectively 2 reds : 1 black : 1 agouti, as obtained (table 2). Further,
such agoutis as came from this cross would be identical in character with the
i^i agoutis. This expectation is confirmed by table 2, second division.

But if the Fi agoutis are mated inter se, then we expect to get zygotes
corresponding with the product of two sets of gametes, each AB +A+B+0,
that is A2B2* +2A2B +2AB2 +4:AB +2A +2B +A2+B2+O. In appearance
these zygotes would fall into three classes, agouti, black, and red, as shown in
the accompanying table.

The agoutis in this (F2) generation, it will be noticed, should be of four
different types, as actually observed. The AB group should produce all three
sorts of young, agouti, black, and red, being
heterozygous in both characters, A and B.
The group designated by A2B would be pure
for A but heterozygous for B. All their young
would be potentially agoutis, but since part
of them would lack black pigment, such would
be red. Hence they would produce only the
two sorts of young, agouti and red ; see table 3.
The group designated by AB2 would transmit
black pigment to all their young, but only part
of these would receive A . Hence they would
produce agouti young and black ones, but
no reds; compare table 4.

The group A2B2 would transmit both black and agouti to all their young;
hence they would produce nothing but agouti young, however mated; com-
pare table 5. The expected proportions of these four groups of agouti animals
are obviously 4:2:2:1. The numbers shown in the tables are 9 : 10 : 16 : 5.
The apparent deficiency of individuals in Group I and excess in Groups II and
III is readily accounted for. Not all the agoutis recorded as derived from an
agouti X agouti cross were seco?id-generation agoutis; many of them were third-
generation agoutis, having been obtained from two successive matings of
agouti with agouti. In that case one or both of their parents may have been
of Groups II or III, in which case the expectation for young of those groups is
increased, while that for Group I is correspondingly diminished. Therefore
both the kinds of agoutis obtained in the experiment and their numerical pro-
portions are in harmony with the hypothesis presented in this paper.

♦The subscript 2 is used (instead of the algebraic exponent 2) to indicate double rep-
resentation of a factor, i. e., a homozygous condition as regards it. (See Castle, 1909.)

Agouti.

Black.

Red.

4AB

2A2B

2 AB2

2B
B2

2A

A,
0

A2B2

1

9

3

4

8

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

SUMMARY.

1. The agouti coat characteristic of wild cavies and of most other wild
rodents is dependent upon the presence in the fur of black pigment disposed
in a definite pattern with red (or yellow).

2. The factors which control, respectively, the development of black pig-
ment and the production of the agouti pattern are independent of each other.

3. The agouti coat is obtained only when both these factors are possessed
by an individual.

4. Only such agouti individuals as are homozygous in both factors breed
true under all circumstances.

5. An agouti animal which is homozygous in A (the agouti factor), but
heterozygous in B (black pigmentation), may produce agouti young and red
ones, but not black.

6. An agouti animal which is homozygous in B but heterozygous in A
may produce agouti young and black ones, but not red.

7. An agouti animal heterozygous in both A and B may produce three
sorts of young, agouti, red, and black. All Fi (reversionary) agoutis produced
by crossing black with red are of this sort. Agoutis of the other three sorts are
obtained only in the second or later generations of agouti young.

BIBLIOGRAPHY.

Castle, W. E., 1905. Heredity of coat-characters in guinea-pigs and rabbits. Carnegie
Institution of Washington Publication No. 23.

1907. On a case of reversion induced by cross-breeding and its fixation. Science,

N. S., vol. 25, p. 151.

1907a. The production and fixation of new breeds. Proc. Am. Breeders' Associ-
ation, vol. 3, p. 34.

Table 1. — Differences among red guinea-pigs as regards the transmission of agouti.

Young by
red mates.

Young by
heterozjgous
black mates.

Young by
homozygous
black mates.

Young by
agouti mates.

R

B

Ag

R

B

Ag

R

B

Ag

1
R B

Ag

I. Homozygous in A.

9 Horton's red

0
0

0
3

10

1

II. Heterozygous in A.

c^2054

9 ]27S, daughter of cf 2054

10

0

0

3
2

10

18
20
19

1
0

5

8
12
17

2
1

6

0
0
0

0

1

9

91280, 91281, daughters of

c?2054

III. Lacking A.

cf 9347

0^2004

44

0

0

1

cf 3496

i

....l....

i

1
1

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

9

Table

2. — Agouti parents producing

red young, black young, and agouti y

1
Young by
red mothers. •

i

Young by i

agouti mothers. ,

Young by
black mothers.

R

B

Ag

R

B

Ag

R

B

Ag

From red X black cross:
cfll78

39
28
9
21
14

16

17

1

8

3

16

7
2
7
8

d'SOlO

cf4812

cTOlSO

2

2

10

cf9152

Totals

111

45

40

2

2

10

From red X agouti cross:
cr2797

13

6

11

(^2944

9

7

14

£3^3982

7
6
8

11
7

13
5
5
8

4
2
2
6
3
2
6
2
5

7
0
4
5
4
6
2
3
4

cfiSSl

2
4

3
2

3
16

cf4882

cf4934

c("4935 .

1

(^7916 .

1

cr7932

0

2

2

cf7978

cr7979 .

cf9190

4

5

17

c?9511

7
3
7
0
5
3

3
2
4
2
2
1

4
2
1

1
3

1

0^9528

(fi9583

cf9602

0^9620

cf9657

0^9684

6

3

9

c?9685

4

4
9
2
6

2
1
6
3
2

0
3
5

1
2

cf9687

0

0

2

^^9698

0^9734

0

1

2

(^9747

Totals

1

133

66

69

25

21

63

0

2

2

From agouti X agouti cross:

0^59

3
2
3
5
1
9
1
8
2

3
1
0
3
1
4
2
5
1

2

1
0
1
0
9
3
2
1

cfl79

0
0

■ 1 1 2 1

cf318

2

1

0^6220

cf9258 ....

1

4

4

cr9259

cr9411

0
2

0
1

2

8

cf9753

0^9993 . .

Totals

34

20

19

3

5

14

0

3 3

Grand totals

278

131

128

30

28

87

0

5

5

Table 3. — Agouti parents producing only red young and agouti young.

Young by
red mates.

Young by
agouti mates.

Young by
black mates.

R

B

Ag

R

B

Ag

R

B

Ag

From agouti X agouti cross:
0^26

4
2
4

I

1
2
17
7
6

0

0
0
0
0
0
0
0
0
0

10
2
4
0
3
1
2

18
6
6

2
0
0

0
0
0

14
5
3

0

0

15

(^31

cfl37

cn47

0

0

3

cfl80

1

0

5

cf309

0^429

cf6219

5
5

0
0

18
17

cr7887

cr7926

Totals

53

0

52

13

0

62

0

0

18

10

REVERSION IN GUINEA-PIGS AND ITS EXPLANATION.

T.^LE 4. — Agouti parents producing only black young and agouti young.

Young by
red mates.

Young by
agouti mates.

Young by
black mates.

B

B

Ag

R

B

Ag

R

B

Ag

From agouti X agouti cross:
cf5

0
0
0
0

1
1
0
2

3

4

'1

cf68

0
0

0

0

2
2

cfl91

0

1

5

cf314

$374

0

1

0

cf434

0

2

4

9437

0
0

1

1

2
1

9462

1

cf6197

0
0
0
0
0
0
0
0

17
5
2
9
2
4
5
1

16
11

2
7
4
6
16
2

0
0
0

6
0
3

11

1
17

cf7819

cf7894

cf8020

0^9810

0

0

7

0^9906 .

0
0

0

.•?

cj'9939

0
0

0
0

3
3

1 j 1

cf9941

Totals

i 1

0

51

91

0

9

46

0

1

5 ! 12 1

T.\BLK 5. — Agouti parents pr

oducing only agouti young.

Young by
red mates.

Young by
agouti mates.

Young by
black mates.

R

B

Ag

R

B

Ag

R

B

Ag

From agouti X agouti cross:
cf 145

0
0
0
0
0

0
0
0
0
0

21
6

8

14

3

0

0

68
4

0

0

16

d'160

0 0

0^181

0 0 6
0 0 57

cr316

0

0

10

9473

Totals

0 0

52

0 0 135

0

0

26

EXPERIMENTAL STUDIES OF THE INHERITANCE OF

COLOR IN MICE.

By C. C. LITTLE.

Research Assistant in Genetics in the Btissey Institution of Harvard University.

Paper No. 19, Station for Experimental Evolution at Cold Spring Harbor, New York.

11

PREFATORY NOTE.

The experiments on which the following paper is based were begun in
the Zoological Laboratory of Harvard University at Cambridge, Massachu-
setts, in November 1907. Since that time more than 10,500 young have
been recorded. In 1909 the animals were moved to the Laboratory of Gen-
etics at the Bussey Institution, Forest Hills, Massachusetts, at which place the
experiments are still in progress.

Throughout the course of the experiments the writer has been encouraged,
aided, and advised by Dr. William E. Castle, to whom any merit that this
paper may possess is chiefly due.

The skillful and accurate representations of the various color varieties are
from water-color paintings from life, by Mr. Eugene N. Fischer, whose interest
has shown itself in the excellent work that he has done.

The experiments have been supported in part by an annual grant from the

Carnegie Institution of Washington made to Dr. Castle "for the continuation

of the study of heredity in small mammals."

Clarence C. Little.

May 1912.

12

CONTENTS.

Pakt I. The Factors Producing Color in Mice.

Page.

Formative and distributive color factors 18

Location of pigment 19

Formative color factors 19

1. The general color factor, Y 19

2. The brown-producing color factor, Br 21

3. The black-producing color factor, B 21

Distributive color factors 22

4. The distributive factor, D 24

5. The distributive factor, P 27

6. The distributive factor, A 30

7. The distributive factor, R 31

8. Sooty yellows and sables 34

The inheritance of spotting 38

Crosses with Japanese waltzing mice 43

Association of characters 44

Part II. ExPERiiMENTAL Data.

Explanation of symbols 47

Color varieties of mice 49

Extended Series 50

I. Black agouti (fig. 1) 50

Black agouti x black agouti 50

Black agouti x dilute black agouti 51

Black agout i x brown agouti 52

Black agouti x black 53

Black agouti x brown 54

Black agouti x dilute brown 55

Black agouti x pink-eyed brown 56

Black agouti x pink-eyed dilute brown 56

II. Dilute black agouti (fig. 2) 56

Dilute black agouti x dilute black agouti 56

Dilute black agouti x black 57

Dilute black agouti x pink-eyed black 57

Dilute black agouti x pink-eyed dilute black 57

Dilute black agouti x pink-eyed black agouti 57

Dilute black agouti x pink-eyed dilute black agouti 57

Dilute black agouti x brown 58

Dilute black agouti x pink-eyed dilute brown 58

III. Pink-eyed black agouti (fig. 3) 59

Pink-eyed black agouti x pink-eyed black agouti 59

Pink-eyed black agouti x black 59

Pink-eyed black agouti x pink-eyed black 60

Pink-eyed black agouti x dilute black 60

Pink-eyed black agouti x dilute brown agouti 60

Pink-eyed black agouti x brown 61

13

14 THE INHERITANCE OF COLOR IN MICE.

Extended Series — Continued. Page.

IV. Pink-eyed dilute black agouti (fig. 4) 62

V. Brown agouti (fig. 5) 62

Brown agouti x brown agouti 63

Brown agouti x pink-eyed brown agouti 63

Brown agouti x brown 64

Brown agouti x pink-eyed brown 64

Brown agouti x dilute black 64

Brown agouti x pink-eyed dilute brown 64

VI. Dilute brown agouti (fig. 6) 64

Dilute brown agouti x pink-eyed dilute brown agouti 65

Dilute brown agouti x brown 65

VII. Pink-eyed broum agouti (fig. 7) 65

Pink-eyed brown agouti x pink-eyed brown agouti 65

Pink-eyed brown agouti x brown 66

VIII. Pink-eyed dilute brown agouti (fig. 8) 66

Pink-eyed dilute brown agouti x pink-ej'ed dilute brown agouti 66

Pink-eyed dilute brown agouti x dilute brown 66

IX. Black (fig. 9) 67

Black X black 67

Black X dilute black 68

Black X pink-eyed black 69

Black X brown 69

Black X pink-eyed brown 70

Black X pink-eyed dilute brown 70

X. Dilute black (fig. 10) 70

Dilute black x dilute black 70

Dilute black x pink-eyed black 71

Dilute black x brown 71

Dilute black x pink-eyed brown 72

XI. Pink-eyed black (fig. 11) 72

Pink-eyed black x pink-eyed black 72

Pink-eyed black x brown 72

Pink-eyed black x dilute brown 73

Pink-eyed black x pink-eyed brown 74

XII. Pink-eyed dilute black (fig. 12) 74

Pink-eyed dilute black x brown 74

Pink-eyed dilute black x dilute brown 74

XIII. Brown (fig. 13) 75

Brown x brown 75

Brown x pink-eyed brown 76

Brown x pinlc-eyed dilute brown 76

XIV. Dilute brown (fig. 14) 76

Dilute brown x pink-eyed brown 76

XV. Pink-eyed broivn (fig. 15) 77

Pink-eyed brown x pink-eyed brown 77

Pink-ej^ed brown x albino 77

XVI. Pink-eyed dilute brown (fig. 16) 77

Restricted Series 78

(o) Dark-eyed intense series 78

XVII. Black-eyed yellow carrying agouti 78

XVIII. Black-eyed yellow without agouti (fig. 17) 78

XIX. Brown-cj^ed yellow carrying agouti 78

XX. Brown-eyed yellow without agouti (fig. 18) 78

CONTENTS. 15

Restricted Series — Continued. Page.

(6) Pink-eyed intense series 78

XXI. Pink-eyed yellow carrying black agouti 78

XXII. Pink-eyed yellow carrying black 78

XXIII. Pink-eyed yellow carrying brown agouti 78

XXIV. Pink-eyed yellow carrying brown 78

(c) Dark-eyed dilute series 78

XXV. Black-eyed dilute yellow carrj'ing agouti 78

XXVI. Black-eyed dilute yellow without agouti 78

XXVII. Brown-eyed dilute yellow carrying agouti 78

XXVIII. Brown-eyed dilute yellow without agouti (fig. 19) 78

(d) Pink-eyed dilute series 78

XXIX. Pink-eyed dilute yellow carrj'ing black agouti 78

XXX. Pink-eyed dilute yellow carrying black 78

XXXI. Pink-eyed dilute yellow carrying brown agouti 78

XXXII. Pink-eyed dilute yellow carrying brown 78

Yellow X yellow, giving only dark-eyed intense young 80

Sooty yellow x sooty yellow, giving only dark-eyed intense young. ... 81

Cream x cream, giving only dark-eyed intense young 81

Yellow X cream, giving only dark-eyed intense young 82

Yellow X yellow, giving intense and dilute dark-eyed young 82

Yellow X yellow, giving intense dark-eyed and intense pink-eyed young 83
Sooty yellow x yellow, giving intense dark-eyed and intense pink-eyed

young 83

Yellow X yellow, giving intense and dilute, dark-eyed and pink-eyed

young 84

Yellow X yellow, miscellaneous 84

Yellow X dilute yellow, giving only intense dark-eyed young 84

Yellow X dilute yellow, giving intense and dilute dark-eyed young .... 84
Yellow X dilute yellow, giving only intense dark-eyed and pink-eyed

young 84

Yellow X dilute yellow, giving intense and dilute dark-eyed and pink-
eyed young 85

Yellow X dilute sooty yellow, giving intense and dilute dark-eyed young 85

Yellow X pink-eyed yellow, giving only intense dark-eyed young 85

Yellow X pink-eyed yellow, giving intense and dilute dark-eyed young . 85
Yellow X pink-eyed yellow, giving intense pink-eyed and dark-eyed

young 85

Yellow X pink-eyed yellow, giving intense and dilute dark-eyed and

pink-eyed young 86

Cream x pink-eyed yellow, giving only dark-eyed intense young 86

Yellow X black agouti, giving only dark-eyed intense young 87

Yellow X black agouti, giving intense and dilute dark-eyed young .... 87
Yellow X black agouti, giving intense and dilute dark-eyed and pink-
eyed j^oung 87

Cream x black agouti, giving only intense dark-eyed young 87

Yellow X dilute black agouti, giving only intense dark-eyed young 88

Yellow X dilute black agouti, giving intense and dilute dark-eyed j^oung 88

Cream x dilute black agouti, giving intense and dilute dark-eyed young 88
Sooty yellow x dilute black agouti, giving intense dark-eyed and pink-

eyed young 88

Yellow X pink-eyed black agouti, giving only intense dark-eyed young . 88
Yellow X pink-eyed black agouti, giving intense and dilute dark-eyed

young 89

16 THE INHERITANCE OF COLOR IN MICE.

Restricted Series — Continued. Page.
(d) Pink-eyed dilute series — Continued.

Yellow X pink-eyed black agouti, giving intense and dilute, dark-eyed

and pink-eyed young 89

Yellow X black, giving only intense dark-eyed young 89

Yellow X black, giving intense and dilute dark-eyed young 91

Yellow X black, giving intense dark-eyed and pink-eyed young 91

Cream x black, giving only intense dark-eyed young 92

Cream x dilute black, giving only intense dark-eyed young 92

Yellow X dilute black, giving intense and dilute dark-eyed young .... 92

YeUow X pink-eyed black, giving only intense dark-eyed young 92

Yellow X pink-eyed black, giving intense dark-eyed and pink-eyed

young 92

Cream x pink-eyed black, giving only intense dark-eyed young 93

Yellow X brown agouti, giving only intense dark-eyed yoimg 93

Yellow X brown agouti, giving intense and dilute dark-eyed young ... 94

Dilute yellow x dilute yellow, giving only dilute dark-eyed young .... 95
Dilute yellow x pink-eyed yellow, giving intense and dilute dark-eyed

yoimg 95

Dilute yellov/ x pink-eyed j'ellow, giving intense and dilute dark-eyed

and pink-eyed young 95

Dilute yellow x pink-eyed dilute yellow, giving only dilute dark-eyed

young 96

Dilute yellow x wild black agouti, giving intense dark-eyed yoimg ... 96

Dilute yellow x dilute black agouti, giving dilute dark-eyed young ... 96

Dilute yellow x dilute brown agouti, giving only dilute dark-eyed young 96
Dilute sooty yellow x dilute brown agouti, giving dilute dark-eyed and

pink-eyed young 97

Pink-eyed yellow x pink-eyed yellow, giving only intense pink-eyed

yovmg 97

Pink-eyed yellow x pink-eyed yellow, giving intense and dilute pink-
eyed young 97

Pink-eyed yellow x pink-eyed dilute yellow, giving intense and dilute

pink-eyed young 97

Pink-eyed yellow x black agouti, giving intense dark-eyed and pink-
eyed young 98

Pink-eyed yellow x dilute black, giving intense and dilute dark-eyed

and pink-eyed young : . . 98

Pink-eyed j^ellow x brown, giving intense dark-eyed young 98

Pink-eyed yellow x pink-eyed black agouti, giving only intense pink-
eyed young 98

Pink-eyed yellow x pink-eyed brown agouti, giving only intense pink-
eyed young 98

Pink-eyed yellow x pink-eyed black, giving only intense pink-eyed yoimg 99
Pink-eyed dilute yellow x dilute black agouti, giving dilute dark-eyed

and dilute pink-eyed young 99

Pinlc-eyed dilute yellow x black, giving intense and dilute, dark-eyed

and pink-eyed young 99

Albinos x pink-eyed brown 100

Albinos x pink-ej'ed dilute brown 100

Bibliography 101

EXPERIMENTAL STUDIES OF THE INHERITANCE OF

COLOR IN MICE.

PART 1.

THE FACTORS PRODUCING COLOR IN MICE.

In the coat of the common house mouse {Mus musculus) three pigments are
recognizable, yellow, brown, and black. No connecting intergradations of color
between these three types are visible. The inheritance of these colors and of
their distribution, both qualitatively and quantitatively, has been the object
of many investigations and is the principal feature of the present paper.

All mammalian color has been found due to melanin pigm^ent. Riddle
(1909) has discussed the process of the formation of melanin pigment and states
that all chemical evidence supports the idea that melanin pigment is the
product of an oxidation process. The substances (chromogens) on which the
oxidizing agents (enzymes) act were found to be tyrosin and certain related
aromatic compounds. It has been further shown that tyrosinase-like ferments,
which occur widely distributed in the organism, act as oxidizing agents, thus
producing melanin compounds. Furthermore, it has been proved that at least
artificial melanins may pass through a series of colors before arriving at the
final stage of oxidation. In such series the earlier stages of oxidation give lighter
colors than the later ones.

Cuenot (1903) advanced an hypothesis to explain the formation of color
by the interaction of a chromogen substance and an enzyme. He called the
chrcmogen the general factor for the production of color, C, and supposed that
in albinos this chromogen substance is lacldng, thus making it impossible for
color to be formed. Riddle, however, states that the nature of the chromogen,
it being very widely distributed throughout the organism, is such that any
theory postulating the absence of this substance would be chemically absurd.
Gortner (1912), however, finds evidence that chromogens in insects may be of
restricted distribution, thus forming color patterns.

At present it is impossible to decide finally between the explanation offered
by Cuenot and that suggested by Riddle. We shall have to await further
chemical evidence to determine whether the albino does or does not lack the
oxidizable substance or substances necessary for pigment production.*

If we assume that there is only one enzyme present to act as an oxidizing
agent, we must assume for it as many different degrees of activity as are re-
quired to explain the occurrence of the various colors known to mendelize (three
in mice, yellow, brown, and black) . If we assume that a different enzyme or

*A recent paper by Keeble and Armstrong (1912) has shovm that in Primula sinensis
lack of chromogen seems to be the cause of albmism, thus favormg the original hj^othesis
of Cu&ot.

17

18 THE INHERITANCE OF COLOR IN MICE.

group of enzymes is responsible for the production of each pigment we must
suppose that in mice at least three such enzymes or groups of enzymes exist.
To determine which of these conditions occurs in mice is not a problem for the
biologist, but for the chemist. The biologist must confine his attention to
determining the number of distinct agencies at work in pigment formation
irrespective of their chemical nature. These agencies, because of their physio-
logical behavior, the biologist chooses to call "factors," and attempts to learn
what he can about their functions in the evolution of color varieties.

FORMATIVE AND DISTRIBUTIVE COLOR FACTORS.

As has already been stated, three pigments (yellow, brown, and black) are
observable in mice. Yellow has been found, by Riddle, to be the lowest in the
scale of mammalian pigments. Nevertheless, in mice no case has been recorded
where yellow alone is present. The eye always has, in addition, brown or
black pigment granules, while in many cases both are present. The same fact
holds good for the coat, so far as observation goes.

These three pigments — yellow, brown, and black — are, however, discon-
tinuous stages. If they are not the products of distinct enzymes they are the
result of distinct grades of activity of a single enzyme. Which of these conditions
holds makes no difference at present, so we may, for purposes of discussion,
refer their causation to three distinct factors, Y for yellow, Br for brown, and
B for black.

Certain animals possess yellow and brown pigment to the exclusion of
black. In such animals, with no evidence of variation in the total amount of
pigmentation, there occur varieties in which the proportion of brown to yel-
low in the coat varies greatly. As the brown increases in amount the yellow
decreases. It is fair, then, to assume that something is acting to convert the
lower-grade pigment (yellow) into the higher grade (brown) . This, we suppose,
is the factor Br already mentioned.

The activity of such a factor may, however, be affected by other factors
which determine the amount of brown formed and its location. Experiment
shoAvs that these assumed factors governing the development of brown are
independent of the hrown-f or ming factor Br, for they can be transferred without
visible alteration to animals with black, anAvice versa. Such factors we may
call distributive.

Black is the highest grade of mammalian pigment and doubtless, as Riddle
states, is a higher oxidation stage of brown; for brown pigment is often, if not
always, seen in black animals, but never the reverse. We may, therefore,
assume a distinct agency for the conversion of brown into black and call this
factor B. If by a given cross this factor B is added to a certain distributional
stage of brown, the corresponding distributional stage of black is obtained,
showing that the factor B is independent of the distributive factors.

Such factors as Y, Br, and B, indicating as they do distinct qualitative
steps in pigment formation, we may call formative factors, in somewhat the
same way as the factors controlling the distribution and amount of pigment
have been considered distributive factors.

FORMATIVE COLOR FACTORS. 19

LOCATION OF PIGMENT.

In wild mammals all three pigments (yellow, brown, and black) commonly
occur in the same hair. In many domesticated or "fancy" varieties, one or
the other pigment prevails almost, if not quite, to the exclusion of the others;
thus yellow, brown, and black varieties arise. Brown varieties (completely
lacking black) occur in certain mammals (e. g., mice, rabbits, guinea-pigs,
and dogs). Theoretically they would seem to be possible in all.

Pigment appears in mice in three general regions. These are the eyes, the
skin, and the hair. The pigment occurs in granules.

In the eyes microscopic examination has shown that the pigment granules
are located in both the retina and the iris. Of these two localities the iris
seems the more permanent pigment-producing center; for when reduction in
the amount of pigment occurs the retina seems the more easily and extensively
affected.

In the skin the pigment is located only a short distance from the surface
in the malpighian layer. In contradistinction to the eyes, which are visibly
pigmented at birth, the skin apparently becomes pigmented only after the
animal is several days old; this is largely because the hairs, in which much of
the pigment lies, are not formed at birth. The pigment granules of the hair
may be clearly observed under the microscope. Bateson (1903), among other
investigators, has determined their location with considerable accuracy and
finds that they are situated in the cortex or outer sheath of the hair, and also
in the interior of the hair in the proximal walls of the medullary spaces.

To recapitulate, we find three general pigment-producing regions in mice :
the eye, the skin, and the hair. The pigments (melanins) produced are limited
to three: yellow, brown, and black — which we consider to be caused by the
action (jointly or severally) of the factors Y, Br, and B. Domesticated or
"fancy" varieties of mice appear to differ from the wild in the partial or com-
plete exclusion of one or more of the pigments. Such exclusion may be the
result of (1) the action of a distributive factor, or (2) the loss of the formative
factor necessary to the production of a particular pigment.

FORMATIVE COLOR FACTORS.

L The General Color Factor, Y.

It has long been recognized by investigators that, in mice, pigmented vari-
eties differ from albinos by a single mendelian unit-character. Thus in crosses
between homozygous self-pigmented and albino animals we find that the first
generation (Fi) consists entirely of pigmented animals. If these first-genera-
tion hybrids be then crossed inter se we should expect in F2 that the ratio 3
pigmented young to 1 albino would be approximated. The experimental results
agree well with this expectation and we have as a result of crossing Fi inter se:

Pigmented.

Albino.

Observed..
Expected. .

598
603

206
201

20

THE INHERITANCE OF COLOR IN MICE.

If we consider, in addition to the above result, those obtained in a similar
cross by other investigators, we may construct the following table :

Pigmented.

Albino.

Allen

240
164
269

418
808
232
49
598

97

57

93

137

255

77

14

206

Crampe

Cuenot

Darbishire

Durham

von Guaita

Parsons-Copeman*

Little

Total observed. .
Expected

2,778
2,785.5

936

928.5

*SeeBateson (1903).

In the cross between the heterozygous pigmented animals obtained in Fi
and pure albinos, where equality of pigmented and albino young is expected,
the following result has been obtained :

Pigmented. Albino.

Observed

Expected

21 ! 16
18.5 18.5

As this cross has been largely neglected in my experiments the numbers are
extremely small. If, however, a table is made showing the work of other inves-
tigators, larger and more valuable results are obtained :

Pigmented.

Albino.

Allen

84
106
31
24
59
21

64
119
33
20
59
16

Darbishire

Durham

von Guaita

Parsons-Copeman

Little

Total observed. .
Exi:)ected

325
318

311

318

All investigators have found that when albino mice are crossed inter se,
only albino young are produced. Albinism is, then, a recessive character.
Cuenot (1903) considered albinism due to the loss of the general color factor
C (chromogen), but for the reasons given by Riddle this interpretation seems
of doubtful validity.

As before stated, mammalian pigment results from the action of an enzyme
or enzymes upon a chromogen substance. Albinos are formed from colored
varieties by the loss or restriction of one of these substances. Present chemical
evidence discredits the possible loss of the chromogen ; the enzyme or enzymes
remain to be considered. Albinos probably lack one or more of these. If

FORMATIVE COLOR FACTORS. 21

further chemical investigation should show that what albinos lack is really
chromogen, as Cuenot supposed, no change in the gametic formulse here used
will be necessary, beyond the addition of a symbol C (chromogen) in the case
of colored animals.

In the writer's opinion the only enzyme which all albinos in common lack is
that which acting alone produces the lowest grade of melanin pigment, namely,
yellow. To this supposed factor I have given the designation Y. The factor
B may or may not be present in an albino, but Br apparently is never lost.
Y then forms the step between color and no color, producing j^ellow when pres-
ent, no color being produced in its absence. This yellow is converted to brown
pigment by the ever-present factor Br, whose action, however, is locally inhi-
bited wherever yellow pigment appears as the final oxidation stage.

2. The Brown-Producing Color Factor, Br.

This factor, in my experience, is never wanting, though its presence is
often at least partly concealed by the factor B, which carries forward the
process of pigment formation from the brown to the black stage. In albinos,
also, when Y (the factor for producing yellow) is absent the factor Br, lacking
the material on which to act, does not function visibly. Thus it is not to be
wondered at that this factor Br has been omitted from the zygotic formulae of
most investigators and that brown is considered commonly the result of the
absence of black. The chemical evidence already given, however, together with
the fact that brown pigment is often, if not always, to be found in black animals,
seems to justify the use of a distinct term to designate the factor that forms
brown. This factor is not to be confused with the absence of the factor for
black formation, which is a pure negation and can not be considered as an active
agent in the formation of anything.

3. The Black-Producing Color Factor, B.

As before stated, this factor is necessary for the production of the highest
stage of mammalian pigment, viz, black. In its absence, the final oxidation
stage is brown, so that we may speak of " animals lacking black" as brown, but
it is conceivable that animals might be found which also lack Br, in which case
the final oxidation stage would be yellow, not brown, and mere absence of black
would not in that case be equivalent to brown.

If we cross, then, animals homozygous for the factor B with animals
entirely lacking that factor, we should expect Fi to consist entirely of heterozy-
gous black animals. By experiment, 589 animals have been produced in this
way, all of which possessed black pigment. We should expect, now, that if such
black animals are crossed inter se, the next generation will consist of three
animals possessing black pigment to one lacking it completely. When this
cross was made the following result was obtained :

Black.

Brown.

Observed

Expected

591
605.25

216
201.75

22

THE INHERITANCE OF COLOR IN MICE.

In the cross between heterozygous black animals and the extracted brown
recessives, where equality of black j^oung and young lacking black are expected,
the following result has been obtained :

Black.

Brown.

Observed

Expected

198
192.5

187
192.5

If brown animals are crossed inter se, only brown young are expected.
The observed facts coincide with the expectation, 822 brown young having
been thus obtained.

It is, then, clear that the presence of the factor for the production of black
pigment and its absence result in a pair of allelomorphic unit characters. In
all the cases above mentioned the heterozygous black animals were indistin-
guishable from the homozygous blacks, so far as external appearances go. The
dominance of black is thus apparently complete. Miss Durham (1911), how-
ever, has recorded the occurrence of a distinct heterozygous form ("chocolate
lilac") in crosses between pink-eyed black ("blue lilac") and pink-eyed brown
("champagne") mice. The writer has made similar crosses with animals of
these color varieties, but is unable to confirm Miss Durham's results.

Pink-eyed black mice vary in depth and intensity of pigmentation, which
fact will be discussed more fully under the head of distributive factors, but the
writer has been unable to detect any greater degree of brownness in the pink-
eyed blacks which are heterozygous ("chocolate lilacs ") than in those which are
homozygous. While it is possible that microscopic examination of the hair
of such heterozygous pink-eyed black animals may reveal a greater relative
amount of brown than occurs in the homozj-gous form of the same color variety,
it seems of doubtful propriety to call the heterozygous form a distinct color
variety. Furthermore, if the distinction between homozygous and heterozy-
gous pink-eyed blacks were a good one, it should be recognizable in the hetero-
zygotes produced by crossing pink-eyed black agouti with pink-eyed brown
agouti types. Miss Durham, however, mentions no such difference between
homozygous and heterozygous pink-eyed black agoutis, and I have been unable
to find any such difference in my own experiments.

Black, in its method of inheritance, forms one of the best examples of a
mendelian unit character. It is, moreover, clearly a positive character which
is dominant over its absence, or chemically expressed it is a higher oxidation
stage epistatic to a lower stage and independent of the latter in inheritance.

DISTRIBUTIVE COLOR FACTORS.

We have seen that three factors act as agents in the formation of the
pigments of mice. We may now consider the factors concerned in controlling
the distribution of pigments thus formed. It is obvious that theoretically the
distribution of pigment may be controlled in two general ways: (1) by the

DISTRIBUTIVE COLOR FACTORS. 23

ability to form either a greater or less total amount of pigment ; or (2) by the
restriction or loss of one or more pigments from certain portions of the pelage,
thus producing " coat patterns." The existence of two distinct factors of each
of these types has been proved by experiment. These will be presently
described.

For a basis from which to calculate increase or diminution in the total
amount of pigmentation (the first category of modifications mentioned), it is
desirable to have, as a standard, some known stock of as nearly constant
pigmentation as possible. For this purpose none seems better than the wild
house-mouse, Mus musculus. There is, to be sure, variation among the wild
individuals of this species, but on the whole it forms as satisfactory and constant
a basis as can be obtained. To the factor producing the degree of pigmentation
observed in the common house-mouse we may give the designation D (density
of pigmentation).

This factor D affects the distribution of pigment granules of the three sorts,
yellow, brown, and black, but there is experimental evidence that another factor
exists which determines the amount of brown and black granules present with-
out affecting the number of yellow granules in the coat. To this factor we may
give the designation P (plenitude or fulness of brown and black pigmentation) .
There is a complete series of color varieties as described by Castle and the
writer (1909) , in which simultaneous modifications of both these factors exist, as
well as two other series in each of which one only of the two factors is modified.

Of the second category of distributive factors, those which cause local
restriction or loss of certain pigments, there are two clear examples in mice.
The first of these is seen in the case of the wild type, where the so-called "agouti"
pattern exists. This pattern results from the activity of a factor determining
the order in which pigments are laid down in the individual hair, and also
producing a differentiation between hairs of the dorsal and ventral surfaces.
This factor we may designate A (agouti) . A factor of this sort produces the
"ticked" coat characteristic of almost all wild rodents. In the absence of ^4.,
animals are self-colored.*

The second factor of this category is a restrictive factor which almost
excludes black and brown pigment from the hair and skin, thus leaving a pre-
ponderance of yellow granules in those localities and producing the so-called
"yellow" varieties of mice. This factor we may call R (restriction). In its
absence colored animals are either agouti if A is present, or self-colored if A
is absent.*

From this very brief description it may be seen that the presence of certain
distributive factors, or modifications of them, determines what color varieties
of mice shall be formed. These distributive factors determine either the total
amount of pigmentation or the relative amounts of j^ellow, brown, and black
that are visible. It is, then, obvious that they are factors dealing with "quan-
tity" of pigment, not with "quality" of pigment, as do the formative factors
Y, Br, and B. Since the "distributive" factors D, P, A, and R deal with

*This ignores spotted forms, which will be considered separately.

24 THE INHERITANCE OF COLOR IN MICE.

quantity of pigment, we might expect that they would show more fluctuations
than do the formative or qualitative factors Y, Br, and B; and such is the case,
as will presently be more fully described.

4. The Distributive Factor, D.

We have stated that this factor is responsible for the degree of density of
yellow, brown, and black pigmentation seen in the common wild house-mouse.
The presence of this factor is allelomorphic to a modification of density of pig-
mentation which we may call " dilute " pigmentation and designate by d. This
dilute type of pigmentation was recognized by Bateson (1903) in mice. At
that time he stated that it consisted of a reduced number of pigment granules,
affecting both the cortex and medulla of the hair. To this the writer may add
that the pigmentation of the skin is visibly lessened in "dilute " forms, and that
the eyes are also affected. When the eye of a "dilute" mouse is examined
under the microscope, reduction in the amount of pigment, as compared with
the densely pigmented forms, is seen to exist. This reduction occurs in both
retina and iris, but is more extensive in the former locality than in the latter.

The dilute forms of rabbits, as compared with the intense forms, show, on
microscopic examination of the hair, a reduction in number of the pigment gran-
ules in the cortex of the hair. The dilution in this case seems transferable to
hair of any color and is therefore comparable to dilution in mice, as it is also
in superficial resemblance, having a streaky and washed-out appearance to the
unaided eye.

In guinea-pigs the condition seems somewhat different. The problem
there does not appear to have been worked out with especial reference to dilu-
tion. There dilute forms do not appear streaky, although the cream type of
reduction seems either directly or indirectly transferable to black and brown.
It seems, however, doubtful whether a true dilution exists in guinea-pigs. There
is no evidence showing a modification of the intense colors, which modification
behaves as a unit character; and it seems probable, from the recent occurrence
of a pink-eyed colored guinea-pig (Castle, 19126), that the reduction of pigment
seen in guinea-pigs is due to a modification approaching that seen in pink-eyed
mice, rather than the dilute modification.

The "dilute" modification affects all three pigments (yellow, brown, and
black), wherever they may occur. Castle and the writer (1909) recognized
this in mice in the "non-yellow " varieties, including those possessing the agouti
factor. Plate (1910) recognizes a dilute series of color varieties, though using
a slightly different nomenclature to designate them. Morgan (1911a) inde-
pendently puts on record the occurrence of dilute animals with the agouti
pattern. Miss Durham (1911) also recognizes the existence of a dilute type
of every color variety. Previous to that time, however, she had not recog-
nized the relation of the dilute agouti animals to the dilute "non-agouti " forms.

Entirely distinct from this modification of the factor for density of pig-
mentation, which produces dilute forms, is the fluctuation of the degree of
density itself. Though "density" and "dilution" act as a pair of allelomor-

DISTRIBUTIVE COLOR FACTORS. 25

phic characters, "density" is subject to considerable fluctuation. Thus we
may have a gradual series of yellow mice, all possessing the factor D, but
varying in depth of pigmentation from an extremely light cream-color to a
deep rich orange. Microscopic examination of the hair of these various forms
shows in "cream" animals a distinctly smaller amount of pigment than in the
hairs of the darker grades of "dilute" yellow animals. Dilute animals also
vary in depth of color. For example, certain dilute browns may be of a dis-
tinctly lighter color than others. We know from the behavior of "density" and
"dilution" in crosses that they are allelomorphic to each other, but we must
admit that they are fluctuating characters and not stable in the sense of the
formative qualitative factors Y, Br, and B. The differences in depth of color
in the case of any color variety, either intense or dilute, are more easily dis-
cerned in those animals which have a preponderance of light pigment, such as
yellows, or in those possessing reduction in amount of pigment due to some
modification, such as dilute dark-eyed and intense pink-eyed mice.

In this connection it is interesting to note the occurrence of certain "coat
patterns" on mice, reported by Morgan (1911a). He describes, among others,
patterns consisting of distinct regions of lighter and darker color. He further
states that when the light hairs are examined under the microscope they show
a lessening of pigment granules in different regions, "a lessening that is a
characteristic feature of the so-called dilute condition." But as reduction in
the amount of pigment occurs in the case of the "light" densely pigmented
and the "pink-eyed" forms, as well as in the dilute forms, evidences of the sort
oft'ered by Morgan can not be considered to establish his conclusion.

Is it not possible that these cases are those of intensely pigmented animals
showing on their coat somatic segregation of certain of the fluctuations that
are seen in dense pigmentation? Such "hghtness" would not be in any way
correlated with dilution, and would appear in homozygous animals as well as in
heterozygous ones.

The writer suggested (19116) that such patterns as were described might
not be a criterion of the heterozygosity of their possessor, but due entirely to
the physiological condition of the animal at moulting. Morgan in reply (1911c)
stated that the cases he described were not "moulting" patterns, which were,
as he stated, " too famihar to * * * call for comment." Yet in his first
paper (1911a) he mentions certain "gray" animals, and figures two, which, as
he states, "show areas of lighter and darker color, and these may come and go
at each moult.' ^

The writer has obtained in a homozygous dilute brown animal (cf317)
regions of clearly lighter hair than the predominant body color of the individual.
These lighter hairs are apparently full-grown, and remained clearly distin-
guishable in this animal for nearly a year, after which the animal died. If this
individual was heterozygous he might, as Morgan states, be considered as giving
"evidence of his dual nature," but his gametic composition is "single;" so per-
haps the "evidence" in the case of the heterozygous animals reported by
Morgan is a matter of coincidence.

26

THE INHERITANCE OF COLOR IN MICE.

The above-described fluctuations in the density of pigmentation are to a
certain extent hereditary. Thus cream-colored mice crossed i77ter se have a
greater number of cream-colored than of deep-yellow young. So, too, from
deep-yellows crossed together the deep-yellow young preponderate, but cream-
colored young may occur as well.

We may now consider the result of crosses between intense animals pos-
sessing the factor D and animals with the modified or "dilute" condition d.
If homozygous intensely pigmented animals (DD) are crossed wtih dilute
animals (dd) only intense young (Dd) are formed in Fi. In my experiments
424 young have been thus produced, all intense, manifesting D. If these het-
erozygotes are crossed together we should expect in F2 the ratio 3 intense
to 1 dilute young. The experimental results are as follows:

Intense.

Dilute.

Observed

Expected

610

608.25

205
203.75

When the heterozygous intense animals are crossed back with the dilute
type the following results have been obtained :

Intense. Dilute.

Observed

Expected

301 197
249 249

Here there is a marked deficiency of dilute animals, which is in all prob-
ability partly due to failure on my part to recognize as dilute certain of the pink-
eyed dilute animals produced during the years 1907-08. During these years
many matings of this type were made. In classifying the young obtained from
these I may have been in error. Thus if we consider the matings made since
1908, which should theoretically produce both dilute and intense young, we
should have the following results :

Cross of heterozygous F,
intense animals inter se.

Cross of heterozygous Fi

intense animals with

recessive.

Intense.

Dilute.

Intense.

Dilute.

Observed . . .
Expected . . .

345
363.75

140
121.25

146
156

166
156

Here there is an excess of dilute animals, which makes it seem probable
that in the matings previous to 1909, of the two types given above, I confused
the dilute and intense pink-eyed forms, often failing to distinguish them cor-

DISTRIBUTIVE COLOR FACTORS.

27

rectly. However, I feel sure that errors of this sort have not occurred since
1909, and the figures given above may be considered as a correct representation
of the observed facts. For the most part the behavior of density and dilution
is clearly that of a pair of allelomorphic unit characters, and they may therefore
be treated as such. Thus dilute animals crossed inter se give, as expected, only
dilute young, 603 such animals having been produced.

5. The Distributive Factor, P.

As before stated, this factor affects brown and black pigment, but does not
affect the amount of yellow present. The modification of this factor giving
rise to the "pink-eyed" series of colored mice, reduces the amount of black and
brown pigment to a very great extent. The reduction affects hair, skin, and
eyes. Miss Durham (1908) has pointed out the fact that the eyes, as the hair,
are not entirely devoid of pigment. In examining with the microscope sections
of the eye of a "pink-eyed" colored mouse, she foundtraces of pigment present,
but in such minute quantities as to make any qualitative analysis impossible.
The writer has examined under the microscope crushed eyes of the brown,
dilute brown, pink-eyed brown, and pink-eyed dilute brown varieties and has
thus been able to trace the steps in the reduction of pigment in these four vari-
eties with fair success. The eyes were prepared bj' dehydrating and clearing
in xylol. The lens was then removed and the iris and retina spread on the
slide and mounted in balsam. When thus prepared, the following conditions
were observed:

(1) In intense-brown animals, the iris is more heavily pigmented than the
retina, but both are thickly pigmented with brown only, no yellow.

(2) In dilute-brown animals, there is reduction of the total amount of pig-
ment, but the retina shows the effects of the reduction more than does the iris.
The pigment is brown only, no yellow.

(3) In pink-eyed intense-brown animals there is very little pigment in the
retina. The iris is moderately pigmented, but much less so than in the dilute-
brown form. The pigment is brown only.

(4) In pink-eyed dilute-brown animals the retina is apparently unpig-
mented, but the iris still contains a small amount of brown pigment. No
yellow pigment is present.

We may now turn to the experimental results obtained in crosses between
dark-eyed animals {PP) and pink-eyed animals {pp) . In this case Fx consists
entirely of dark-eyed animals {Pp), 1,085 individuals having been thus obtained,
all dark-eyed and to external appearances indistinguishable from homogyzous
dark-eyed animals. These Fi heterozygotes crossed inter se have given the
following result :

Dark-eyed.

Pink-eyed.

Observed

Expected. . . .

1,673
1,597.5

457
532.5

28

THE INHERITANCE OF COLOR IN MICE.

If these results are added to those obtained by Miss Durham in similar
matings we have :

Dark-eyed.

Pink-eyed.

Durham

876
1.673

303
457

Little

Total observed. .
Expected

2,549
2,481.6

760
827.4

The result is not strikingly close to the expected numbers. There is in my
experiments a deficiency of pink-eyed animals too extensive to be overcome by
the excess of pink-eyed obtained by Miss Durham. The difference in result in
the two cases may be considered as probably too great to be due entirely to
chance.* Furthermore, in the following cross the result is still more aberrant
and again there is a lack of pink-eyed animals. The cross is that of heterozy-
gous dark-eyed animals (Pp) with pink-eyed animals (pp) . Equality of dark-
eyed and pink-eyed young is expected.

Dark-eyed.

370

327

Pink-eyed.

284
327

Observed . . .
Expected. . . .

Here, if the higher numbers (gained by adding Miss Durham's results) are
considered, the numbers are closer to equality, though still widely unequal:

i

Dark-eyed. Pink-eyed.

Durham

105
370

113

284

Little

Total observed . .
Expected

475 397

436 436

It is possible that in the "pink-eyed" animals of my strain some constitu-
tional weakness exists, either directly connected with the "pink-eyed" modi-
fication or to a marked degree correlated with it, which tends to cause a higher
degree of mortality among the pink-eyed than among the dark-eyed young. I
have tried, so far as possible, to record the eye-color of j^oung at birth, but have
failed in many cases. Even if it had been possible, it would not be safe to state
that animals with apparently unpigmented eyes were all pink-eyed colored
forms, for albinos at birth are indistinguishable from the pink-eyed colored
series.

When "pink-eyed colored animals are crossed inter se, only "pink-eyed"
animals have been produced; 496 young have been thus obtained.

*Using the method described by East & Hayes (1911) p. 37, we find that the deviation
from the expected ratio is 0.0810, while the probable error is ±0.0752.

DISTRIBUTIVE COLOR FACTORS.

29

"Pink-eyed" colored varieties are much ''yellower" in appearance than
their corresponding dark-eyed intense and dilute forms. This is due to two
facts :

(1) That in such forms as the pink-eyed black agouti and pink-eyed brown
agouti (both intense and dilute) the yellow hand of the agouti pattern is left fully
pigmented, while the black and hrown pigment in the same hairs is much reduced in
amount. Similarly pink-eyed yellow animals possess fully pigmented yellow
hair and thus have as heavily pigmented coats as do the dark-eyed yellow types.

(2) In the pink-eyed black and pink-eyed brown varieties (intense and
dilute) there are no yellow pigment granules in the hair, but the extremely small
amount of black or brown pigment present gives the optical effect of an animal
with yellow pigment. This is especially marked in the case of the pink-eyed
brown variety.

The mutual independence of the factors D and P, and of their modifica-
tions d and p, was recognized by Castle and the writer (1909) and found to hold
good in all the color varieties, whether possessing the agouti pattern or not.
At that time we reported the cross of a dilute "dark-eyed" animal with an
intense "pink-eyed" animal, resulting in the production of a "dark-eyed in-
tense " Fi. We had then only a small number of F^ animals from such crosses,
but those showed that the four theoretical classes of offspring were produced.
In similar crosses we have now obtained the following result:

Dark-eyed
intense.

Dark-eyed
dilute.

Pink-eyed
intense.

Pink-eyed
dilute.

Observed . . .
Expected . . .

71

77

32

25.7

28
25.7

6

8.6

Other crosses showing the independence of D and P have been made, and
the results all follow the expectations with reasonable accuracy. Miss Durham
(1911) has also recognized the independence of D and P, but without giving
numerical results showing the occurrence of the intense and dilute types of the
various pink-eyed color varieties. She, however, recognizes the independence
of pink-eye and dilution only in those mice "in which yellow is absent." The
fact that their independence has been observed and experimentally proved in
animals (agouti) in which yellow is present seems to remove this restriction.
Thus, for example, the cross reported in 1909, and already referred to, shows
that their independence is clear-cut, even in the individual hair, and that the
presence of yellow in the hair aids in showing their independence; for in the
dilute agoutis (brown or black) all the pigment in the hair is reduced in amount,
while in the pink-eyed agoutis (brown or black), the yellow band in the hair is
as heavily pigmented as in dark-eyed agouti forms.

We may now consider, in order, the two factors which have to do with the
relative distribution of the three pigments, yellow, brown, and black, in the
hair and skin. These factors A (agouti) and R (restriction), already briefly
described, have certain characteristics in common, and evidence exists (as will

30 THE INHERITANCE OF COLOR IN MICE.

be discussed later) that they may be closely related. Their sphere of action is
limited to the hair and skin, to the exclusion of the eye. In this respect they
differ fundamentally from the distributive factors D and P, already described.

6. The Distributive Factor, A.

This factor was first recognized by Cuenot (1902) under the designation of
G (firm), as producing the pattern seen on the coat of the wild house-mouse ; but
he erred in considering the factor G as allelomorphic to the factor N {tioir) for
the production of black pigment. Castle (1907o) proved that in guinea-pigs
the agouti pattern is a unit character allelomorphic to its absence. Guided
by this hypothesis he formed a new color variety of guinea-pig (cinnamon).
Furthermore, he proved (1907a) that the agouti pattern might be carried by
certain red animals, which when crossed with blacks produced agouti young in
the first generation. By experimental test it was proved that all black animals
behaved the same in the crosses made and that the reds differed. Morgan
(1911a) quotes Castle as stating that in the above-mentioned crosses both the
blacks and reds were able to transmit the agouti type of coat. Having thus
misquoted Castle, Morgan offers as a suggestion the explanation which Castle
proved was correct in 1907.

The agouti pattern consists in mice (Allen, 1904) of two chief types of dor-
sal hairs: (1) Those having a fine block tip, a sub-apical band of light ochraceous
color (occupying about one-fifth of the hair) and a dark plumbeous basal por-
tion. (2) Others, less numerous, are black throughout.

The ventral hairs Allen describes as possessing a distal half, which is dirty
white to pale ochraceous buff, and a basal half which is plumbeous. Castle
(19076), in describing the agouti pattern in guinea-pigs, states that the tips are
black in hairs showing the ticking; then follows a yellow or red band, and then
the hair is black to the base. Both of these investigators find that the ' ' ticked ' '
hairs have black tips, as does Hurst (1905) in the case of rabbits.

Morgan (1911a) states that he has obtained black animals which have cer-
tain of their hairs brown-tipped. These he characterizes as agoutis without the
yellow band and further states that the ticked hairs in the coat of ''agouti"
animals are brown-tipped. It is obvious that he is dealing with a color pattern
in his "gray" (agouti) animals which is not identical ivith the agouti pattern as
described by other investigators. It tends, therefore, to confusion to treat the
pattern that he is dealing with as agouti. Furthermore, it seems probable
that the blacks, which he reports as having ticked {brown-tipped) hairs, do not
possess a factor in the least comparable with the "agouti" pattern. Morgan
himself states that these brown-tipped hairs occur oyily in heterozygous black
mice. The question suggests itself, how can mice possess, as a result or neces-
sary concomitant of heterozygosis, a pattern which is the characteristic of a
homozygous wild race?

Bateson (1903) stated that in black mice the tips of the large contour hairs
are often brown. Ticked hairs in non-agouti (black) mice are not, then, a new
development, and as black mice have been long used in experiments and have

DISTRIBUTIVE COLOR FACTORS.

31

never been found to transmit the agouti pattern, it seems that Morgan has been
misled by the superficial appearance of "ticking" in the hair.

That superficial ticking is not identical with the agouti pattern is observ-
able in the case of ' ' sable ' ' mice, as will be more fully discussed later. It is also
observable in certain "dingy" or "smoky" young produced by Himalayan
rabbits. In this case there may be as many as two light bands in the "ticked "
hairs, the dark portions of which seem to contain a small amount of black pig-
ment producing the dingy appearance alluded to. In such cases it is known
that neither parent carries the agouti pattern, yet here are hairs with an appa-
rently similar ticking; therefore not all ticking of rodent hairs is due to the
same factor.

We may now consider crosses in which the "agouti" pattern is involved.
In the cross between homozygous agouti and non-agouti forms, Fi consists
entirely of agouti (black agouti or brown agouti) animals, 344 young having
been thus obtained. When certain of these heterozygous Fi animals were
crossed inter se there were obtained :

Agouti.

Non-agouti.

Observed ....
Ex-pected

257
243.75

74
81.25

If the heterozygous Fi agoutis are crossed with non-agouti mice we should
expect equality of agouti and non-agouti young. In this cross I have obtained :

Agouti.

Non-agouti .

Observed ....
Ex-pected

194
182

170

182

When non-agouti animals are crossed inter se only non-agouti young are
produced, the numbers in this case being 1,812.

From the result of these crosses it may be stated that the agouti pattern,
though it may or may not he a single unit character, certainly behaves like one.
Until it has been shown to be complex, the only safe course seems to be to con-
sider it simple and allelomorphic to its absence.

7. The Distributive Factor, R.

This factor produces the true yellow varieties of mice by an almost com-
plete exclusion of brown and black from the skin and hair. In those localities,
therefore, the process of pigment formation is carried only as far as the "yellow"
stage. The chief point of importance in connection with the appearance of
yellow in the coat is this: Yellow-pigment granules, so far as experimental evi-
dence goes, never appear in the skin and hair of mice unless certain distributive
factors {A or R) are present to exclude part or all of the brown and black from
those localities. In such regions oxidation beyond the yellow stage is impos-

32 THE INHERITANCE OF COLOR IN MICE.

sible. Ill the absence of factors A and R the oxidation proceeds, over the whole
coat, to the stage determined by the presence of the formative factors, Br or B.

"Yellow" mice are not produced by a factor comparable to the factors Br
and B, but by a factor having an entirely different function, namely, that of
restriction or inhibition. The nature of the agouti factor A is also restrictive,
though in a much more limited degree. Thus the factors A and R have func-
tions which are roughly comparal^le, in that they both "restrict" the formation
of black and brown, allowing yellow to take their place.

In studying the relation of "yellow" to black agouti mice. Miss Durham
(1911) has obtained extremely interesting and valuable results. Thus she has
in two cases obtained a "yellow" animal from agouti parents, Avhich is a rever-
sal of the ordinary conditions. The fact that such a reversal of dominance can
exist is of extreme importance and adds one more peculiarity to the genetic
behavior of "yellow " mice. In all crosses made by the WTiter, however, yellow
has proved epistatic to black agouti. When the black agouti young obtained
from yellov/s were crossed inter se, 71 young were obtained, none of which were
3^ellow.

When cream (fig. 18) is crossed with ivild Mack agouti the yellov/ young
obtained are cream; thus 3 cream and 2 light-black agouti young have been
obtained. The Vvdid black agouti possesses potentially a "cream" degree of
pigmentation. If creams are crossed with black agouti animals produced by
synthesis in experiments with other varieties, the yellow young produced are
yellow, not cream, thus 12 yellows and 6 intense non-yellow young have been
produced. These synthesized agoutis, then, are not potentially cream, but are
darker-colored members of the series which fluctuates between cream and deep
orange.

Cuenot (1905) reported the fact that homozygous yellow mice were not
obtainable in his extensive experiments. This fact has been corroborated
by other investigators. Cuenot (1911) has stated that tlie factor R, which
restricts brown and black from the pelage, is the same in function as the factor
Y, which forms the "yellow" degree of oxidation, and that there is no need of
including both in the gametic formulae of mice. But chemical evidence indi-
cates that all brown or black pigmented mice must possess the ability to form
yellow pigment in order to form the higher stages, viz, brown and black.
Furthermore, they must possess this at times in all their gametes, otherwise a
homozj'gous brown or black animal would be impossible. Y, therefore, which
produces the yellow degree of oxidation is riot comparable to R, which can occur
in only one of the gametes of a zygote and which restricts brown and black
forming material, thus producing visibly yellow mice.

Mice homozygous in Y are represented by wild black agoutis, but mice
homozygous in R need not occur, by any present theory, nor do they occur in
actual experiment.

Yellow varieties of mice exist, as Cuenot (1911) recognizes, in all the color
varieties in which non-yellow mice exist. Their external appearance, however,
leads one to identify only six types, namely : (1) black-eyed yellows, brown-eyed

DISTRIBUTIVE COLOR FACTORS.

33

yellows, black-eyed dilute yellows, and brown-eyed dilute yellows in the "dark-
eyed" series; (2) pink-eyed yellows and pink-eyed dilute yellows in the pale
series. The experimenter can not distinguish by external appearances the black
eyed and broAvn-eyed forms of the pink-eyed yellow series, and so must class
them together unless breeding tests be applied.

The "yellow" coat of mice is due to as true a pattern factor as is the agouti
coat, and the investigator errs when he considers the "yellow coat" a lower
stage of development of a black or brown coat. Yellow pigment appears in the
ticked or agouti coat by the action of a factor whose function is of a restrictive
or inhibitive nature. In a very similar fashion yellow pigment appears on a
greater scale in the coat of the "yellow" mouse.

"Yellow" in mice is no more allelomorphic to gray than is gray allelomor-
phic to black. Castle, as already stated, has shown that the factor which pro-
duces the ticked or gray coat is allelomorphic to its absence, not to black or any
other pigment. It is an excellent thing to simplify gametic formulse when this
can be done with the support of experimental evidence, but the experimental
work should precede the "simplification" unless a false impression is to be
produced.

If yellow animals are crossed with non-yellow, equality of yellow and non-
yellow young is approximated. The following numbers have been obtained :

Yellow.

Non-yellow.

Observed ....
Expected

864
868

872
868

Several litters of young have been produced b}^ yellows nnxted inter se since
the publication in 1919 of figures showing approximately a 2 to 1 ratio. The
additional observations are:

Yellow.

Non-vellow.

•

Observed

48

45.2

51

20

22.6

17

Expected, 2 to 1

Expected, 3 to 1

If these figures be added to those obtained by Miss Durham (1911), by
Cuenot (1903), and by Castle and the writer (1910), the following result is
obtained:

Yellow.

Non-yellow.

Mi.ss Durham (1911)

Cuenot (1903)

448

263

1,024

48

232

100

538

20

Castle & Little (1910)....
Little (1910 and 1911)

Total

1,783

1,782.2

2,004.75

890
891
668.25

Expected, 2 to 1

Expected, 3 to 1

34

THE INHERITANCE OF COLOR IN MICE.

The relation of the restriction factor R to the factors P and D has been
considered briefly under the head of those factors. The occurrence of dilute
yellow mice, clearly distinguishable from ''creams" or "light yellows," was
reported by the writer (1911) in the dark-eyed color series. Since that time a
few crosses have been made with pink-eyed dilute yellows and they have been
found to conform in their general behavior with other yellow varieties. They
apparently can not be obtained in a homozygous state, and when crossed inter
se give yink-eyed dilute yellow and pink-eyed dilute non-yellow, as 2 to 1.

Dilute yellow animals, whether clear, sooty, or sable, are in appearance
more heavily pigmented than are the lightest creams; but they, as the intense
yellows, are found in shades of yellowthat vary between cream and deep orange.
Any and all dilute yellows have, however, the characteristic streaky, washed-
out look of the dilute black or dilute brown forms. In crosses, dilute yellows
bred inter se have given :

1

Dilute
yellow.

Dilute
non-yellow.

' Observed

Expected, 2 to 1. .
Expected, 3 to 1 . .

100

102.67

115.5

54

51.33

38.5

It will, then, be seen that dilute yellows, like intense yellows, give a 2 to 1
ratio, the homozygous type being apparently unable to develop.

Dilute yellows crossed with dilute non-yellows have given the following:

Dilute
yellow.

Dilute
non-yellow.

1

Observed 61

Expected ; 58.5

56
58.5

8. Sooty Yellows and Sables.

It is well-known that varieties of yellow mice exist which have a varying
amount of dark pigment (brown or black) in the hairs on their dorsal and lateral
surfaces; this produces types of yellow known as "sooty yellows" or "sables."
The amount of dark pigment varies from a few dark hairs, scattered along the
mid-dorsal line, to a condition in which the whole dorsal and nearly all the
lateral surfaces are dark, leaving yellow confined to the more ventral portions
of the sides and to the belly. A series of arbitrary grades indicating the degree
of sootiness has been constructed within the past year. By this means it is
hoped to get more accurate ideas as to the nature of sooty yellows. The grades
are based upon skins of "sooty" animals and these skins are used as the types
by which the living animals are graded. Several experiments have been at-
tempted with the sooty yellows, but all these are still in a preliminary state.
Higher numbers of individuals from experiments now in progress may tend to
change the conclusions to be drawn from work with this varietj'.

DISTRIBUTIVE COLOR FACTORS.

35

The sooty yellows in my stock are most of them homozygous for black, i, e.,
BB. The question arose, how would such sooty forms behave if crossed with
clear yellow lacking B. Experimental evidence shows that sooty yellows hav-
ing only one dose of B are not as dark as those with two doses.

Thus 7451 sooty (grade +li) when crossed with sooty yellow female 7452
(+1|) gave sooty yellow young, the average grade of which was+1. The
same male when crossed with a brown ( 9 7730) gave yellow young, the grades
of which averaged +.31. The writer has never obtained a sooty yellow or sable
that did not carry the factor for the production of black pigment (B) in at least
half its gametes. Several hundred sooty yellows or sables have been obtained.

Yellows having one dose of B when crossed inter se should give (besides
yellows of their own type) those lacking B entirely as well as those having two
doses of B. If the ''sooty" character segregates, 25 per cent of the yellow
animals should approximate the grade of their "sooty" grandparent, 50 per
cent should resemble their parents, and 25 per cent should be clear yellow like
their other grandparent. A table follows, showing the results of two families
in this experiment. The numbers of young are as yet small.

Sooty yelloiv x broivn.

Grade of
sooty
grand-
parent.

No. of Fi

yellow
yoiing.

Average

grade of

Fi yellows.

No. of F.
yellow
young.

Grades of F^ yellow young.

Average

of F2

yellow

young.

0

.25

.50

.75

1.00

+ .25....
+ 1.25....

12
4

+ .06
+ .31

7
6

7
1

2

2

i

+ .00

+ .42

It will, then, be seen that when the sooty grandparent is of low grade, +1,
nearly clear yellow, his ''sooty" character is to all intents and purposes lost in
the cross with brown. It fails to reappear in F2, so far as the animals obtained
are concerned. When the grade of the sooty grandparent is 5 times as great,
that is, +1.25, it will be seen that the average grade of Fi is also about 5 times as
great (that is, 0.31 as compared with 0.06). Also in F2 darker forms are
obtained which may approach the degree of sootiness seen in the grandparent.

Miss Durham (1911) is able to distinguish clearly between " sooty yellows "
and "sables." In this connection she characterizes "sables" as produced in
crossing yellows with blacks or browns. They have a dark black or brown
streak down the middle of the back, while the rest of the mouse is yellow.
Generally the hairs in the dark streak show a ticked pattern independent of
whether the animal carries agouti or not. She has had certain animals (sables)
which were dark-pigmented except for a yellow belly. Such animals always
molted out sables. She says "sables" are not to be confused with sooty
yellows, which result from mating yellow with black, and are dirty color all
over with no pattern. She finds that yellows crossed inter se may give "sables,"
and that "sables" crossed inter se may give yellows, and that matters are

36 THE INHERITANCE OF COLOR IN MICE.

further complicated by the occurrence of so-called "reversed sables," in which
the dark hairs had yellow tips and bases, with a dark subapical band.

The writer must confess that he is unable to draw a clear line between
"sables" and "sooty yellows" in all cases. The term sooty yellow is there-
fore intended in this paper to cover both varieties.

It is possible to explain the appearance of sooty yellows on the basis of
fluctuation in activity of the factor R, restriction. Thus, when R is present in
full strength the animal is clear yellow; if R is slightly weaker, some dark
pigment shows itself.

The amount of dark pigment visible becomes progressively greater as the
factor R becomes weaker or takes on a rhythmical activity. Thus, if R is
hampered in activity during the growth of the first part of the hair, we have a
dark tip formed. But if R comes into full activity again, a yellow band results,
followed by a second weakening of R, resulting in a dark base to the hair.
This would account for the superficial similarity to the agouti pattern. " Re-
versed sables" may possibly result from a reversal of the order in which the
strong and weak periods of R occur. So, too, those very dark sooty yellows
that lack the ticked-hair pattern may be considered due to continued weakness
of the factor R during development of the hair of the first coat. When the
second coat is formed, however, the factor R makes its appearance felt more
strongly and an ordinary type of sable results, with less dark pigment than was
present on the first coat.

In all such cases the idea is present that there is Ciuantitative variation in
the activity of the restriction factor R, showing itself in the varying amount of
black or dark pigment present. If such weakness is due to any interchange of
substance between gametes or any quantitative inexactitude in the process of
segregation, we should expect that repeated crosses of sooty yellows with
blacks would tend to produce much weakened yellows (i. e., very dark sooty)
with much black pigment, as well as modified blacks with some yellow pigment
present. While this experiment has not yet been carried to large numbers it
may be of interest to record the pedigree of one family :

Generation.

Parents.

Progeny.

I

c?4347 sooty yel. x 9 4346 black
cf7451 sooty ycl. x 9 7729 black

0^1029 sooty yel. x | ^ J^gglblack.

9 sooty, av. + ■ 78, and 2 blk.
4 sooty, av. + 1 . 25, and 2 blk.

6*sooty, av. + 1.50, and 7* blk.

II

Ill

*Among these sooties was cf 1318 (fig. 20) graded +3, darker by four "one-quarter"
grades than any sooty previously obtained. The best previous was +2. Among the blacks
in the same litter was cf'lSlG, the first visibly modified black known to be homozygous in
hundreds of black animals that I have seen. His coat is distinctly tawny.

"Sooty yelloAvs" and "sables" have not been reported in the pink-eyed
series. This accords with the results expected by theory, for the modification
of the factor P, which produces pink-eyed forms, reduces the brown and black

DISTRIBUTIVE COLOR FACTORS. 37

pigment granules in the hair to such a degree that we should expect the dark
pigment in the hairs of dark-eyed ''sooty," yellows, and ''sables" to be entirely
lost in corresponding pink-eyed forms.

AVe have seen that the factor which produces "yellow" mice is dominant
to its absence and is (in function) an inhibitor or restrictor of brown and black.
It is interesting to compare with this condition the conditions observed in
rabbits and guinea-pigs.

In rabbits Castle (19076) has shown the occurrence of two types of "yel-
low" animals, both of which are hypostatic to non-yellow forms. The process
of restriction, if it be such, that produces the yellow type of coat in rabbits is
not as extensive as that which produces the clear yellow of mice. Thus all
yellow rabbits Avhich lack the factor A are, as Castle has shown, sooty; that is,
the}' have considerable black pigment in the hair, v/hich produces not a clear
yellow, but a dull or dingy j^ellow coat. Such a condition, varying or fluc-
tuating as it does in sooty yellows of the same gametic composition, may
be called due to an imperfectly recessive character; that is to say, a condition
which shows varying amounts of a dominant character on extracted recessive
individuals, may be considered as showing imperfect recessiveness. Such a
condition would be more explicable on the grounds that "yellow" in rabbits
appeared as a restriction of black and brown than as a loss of those substances.
Yellow in rabbits would then be, according to a nomenclature and system sug-
gested by Dr. Castle, due to a semi-potent restrictive factor. By semi-potent is
meant a positive character which must be present in all the gametes of an indi-
vidual, for its manifestation in the zygote.

With such semi-potent characters may be contrasted uni-potent characters,
which cause visible effect in the zygote when present in one-half its gametes.
An example of this category of factors is seen in the factor R, in mice, which we
have been discussing.

In guinea-pigs, however, we seem to have a different condition, in that
sooty-yellow animals are very rarely formed. Thus yellow guinea-pigs ex-
tracted as recessive from a black race are, in a great majority of cases, clear
A^ellows, whether they are "reds" or light "creams." The occurrence of such
clear yellows is more explicable on a theory demanding loss of brown and black
pigment from the skin and hair than from a process of restriction, for it has
been seen that restriction is at times an extremely imperfect process, subject to
frequent fluctuations in degree of activity, while loss is or should be a clear-cut
process, removing the possibility of frequent fluctuations by completely remov-
ing the materials from which such fluctuations arise.

In studying "yellow" color varieties similarity of color should not have suf-
ficient value in analysis to argue a comm.on origin of all yellow forms. Discus-
sion of such a question as the origin and physiological significance of different
types of yellow must, at least for the present, be based on generalities, since defi-
nite evidence is wanting. On the evidence given by such general facts, the writer
has above outlined a possible explanation of the observed conditions, fully reahz-
ing, however, that at best such an explanation is incomplete and unsatisfactory.

38 THE INHERITANCE OF COLOR IN MICE.

THE INHERITANCE OF SPOTTING.

Spotted forms exist in all the various color varieties of mice. Such
spotted or piebald animals possess an amount of white varying from a few
white hairs to a condition in v/hich pigment occurs in the eye alone, all the coat
being white. Spotting is at present one of the least-understood color phenom-
ena, and further research is necessary before the correctness of any hypothesis
concerning it can be proved. Nevertheless, it seems advisable to consider the
physiological nature of spotting and to attempt to eliminate such theories as
may be shown, even with our present imperfect knowledge, to be incorrect.
As stated in the first part of this paper, present chemical knowledge leads us to
the belief that all mammalian pigments are melanins.

Superficially, spotting appears to be partial albinism, and the question
naturally arises as to whether it really is due to the same cause or causes that
produce albinism, such cause or causes manifesting their presence in a lesser
degree or in a mosaic condition.

Experimental evidence does not support a theory which postulates the
common origin of white produced by spotting and that produced by albinism.
If spotting is partial albinism we should expect, when spotted animals are
crossed with albinos, that only spotted or albino animals would be obtained.
Among the results observed by various investigators, none show better the fal-
lacy of this point of view than the classic experiments of Darbishire (1902) with
crosses of spotted waltzing mice and albinos of gray (black agouti) ancestry.
The appearance of uniformly pigmented animals in the first generation of this
cross proved conclusively that the processes producing the white of spotted
coats and the white of albinos are not only non-identical, but are fundamen-
tally different.

Since a difference in origin of these two types of white exists, the next
matter of interest is to find out whether the difference lies in the qualitative
chemical make-up of the two whites or in the nature of the distributive proc-
esses which allow them to appear in the hair.

Experiments bearing upon the qualitative nature of the two types of white
have been made by Mudge (1909a) on piebald (spotted) and albino rats. He
treated the pelage of animals of both these varieties with chemical agents cal-
culated to provide an oxidizing substance which might act upon the chromogen
in the white portions of the coat, if such a chromogen were present there. He
found that the white hairs in both categories of animals became yellow, both
reacting equally to the agent provided. A few months after the publication of
his work on rats he obtained similar results in piebald and albino mice, by
slightly varying the composition of the agent used.

The writer does not possess sufficient knowledge of chemistry to comment
upon the ultimate value of the work done by Mudge, but in absence of contrary
evidence it seems that his work, especially as it deals with the very types that
we are considering, is worthy of confidence and forms a suitable base from
which to draw conclusions.

THE INHERITANCE OF SPOTTING. 39

If, as Riddle states, it seems absurd to postulate the complete loss of chro-
mogens in albinos, we must suppose that an enzyme or enzymes have 6een lost, in
order to prevent the formation of pigment. If, now, the work of Mudge shows
that the white of spotting lacks the same class of substance as the white of
albinism we must say that here also the enzyme or enzymes are absent from the
white areas. But by the work of Darbishire, already alluded to, and that of
later investigators as well, it is shown that the processes concerned in the
origin of the two types of whites are not identical. We must then, by elimi-
nation, come to the conclusion that the nature of the processes which control
the distribution of the enzyme or enzymes differs in the two categories.

We have seen that the amount of pigment in the hair of intense pigmented
animals is dependent upon the cooperation of two factors, D and P. In the
wild Mus musculus the pigment occurs distributed over the entire coat, and the
animal is said to be self or uniformly pigmented.

We have supposed that the distribution of pigment is controlled by certain
factors. Thus we have supposed that density of pigmentation is controlled by
a factor D, by the activity of which a certain amount of pigment is formed in
eyes and skin and hair. We have recognized a quantitative modification of
this factor in the case of dilute varieties, possessing less pigment. Since this
modification affects all three pigments (yellow, brown, and black) and since
we have supposed brown and black to be higher oxidation stages of yellow, it
seems logical to consider D a factor modifying Y, and in this way also modifj^-
ing Br and B, which are, so to speak, converted Y. When D is modified in
amount, less Y is converted to the brown or black stage. This is the condition
seen in dilute animals. Logically we should expect another type of modifica-
tion of F. In self animals Y is distributed over the whole coat. We should
expect some forms in which Y was distributed only to certain portions of the
body. This modification is seen in the forms in which white spots occur. Such
white areas may be considered as those from which the F-forming substance is
absent. Thus the relation of these factors to one another may be roughly
shown as follows:

' Distributed in a certain f Modified in amount to

degree of density = D \ form dilute varieties = d

Distributed to a certain I Modified in amount to

extent (self) =.S \ form spotted varieties =s

If we designate the spotted (piebald) forms by the letter s, we may logi-
cally consider the unmodified self forms as being of the constitution S. We
would expect, then, that in crosses between a spotted race of known gametic
formula (s) and a self race of formula {S) a mendelian monohybrid ratio would
be observed. That such is the case has been recorded by Doncaster (1906) and
by Castle and MacCurdy (1907) in the case of "hooded" and self rats. Such
a type of spotting as that seen in the hooded rats is, then, a unit character so
far as its behavior in crosses is concerned.

Cuenot, working with mice, has found that spotted forms exist, varying
greatly in proportion of white to colored areas. This series of spotted forms
he accounts for by supposing that there are present a number of small factors

Color producing
substance Y

40 THE INHERITANCE OF COLOR IN MICE.

for the production of spotting (panachure). These he designates pi, pz, pz,
Pa, ... . etc. Cuenot is by no means alone in favoring multiple factors as
an explanation for spotting. It is easy and attractive to imagine a factor for
every observed degree of spotting The various types of spotted animals seem
clear-cut, the colored and white areas seem to form a marked contrast, and the
presence of many factors to produce these many forms gives an air of finality
to an hypothesis which is alluring.

The advantages of a multiple-factor hypothesis, however, are rendered
dubious by the observed occurrence of strains which show that a certain amount
of fluctuation exists in the manifestation of even these assumed multiple units.
It is questionable whether it would be possible to distinguish between a result
produced by multiple factors of the number necessary to explain the occurrence
of the various spotted forms and a continuous series formed by fluctuation of
of the original modification which produces spotting.

Observed experimental facts, however, do not favor a multiple-factor
hypothesis. Thus, if multiple factors for spotting existed, the black-eyed
white variety would possess the greatest number of these spotting factors.
Cuenot in mice and Castle in guinea-pigs found that spotting was recessive to
self in crosses. Therefore the black-eyed white forms would possess a great
number of recessive spotting factors, pi, p^, ps, pi, ps, pe, etc. How, then,
could two such animals when crossed inter se give in their young practically the
whole gamut of spotted forms, as Castle (1905, p. 45), found was the case.

In a somewhat similar way the presence-and-absence hypothesis meets
with trouble in the same cross, i. e., black-eyed white X black-eyed white. The
spotting from which the black-ej^ed whites are derived is recessive. It is,
therefore, according to the presence-and-absence hypothesis, as advanced by
Bateson and Punnett, due to the loss or absence of a factor or factors for uni-
formity of pigmentation. Yet two animals having, according to this theory,
lost the factors for pigment production in the coat, give young which often
have a large amount of pigment on the coat. The presence-and-absence
hypothesis, in order to explain this case, must imagine a degree of fluctuation
in the manifestation of the spotting character which makes proof of the
multiple-factor hypothesis difficult if not impossible.

In the writer's opinion, present knowledge of spotted forms is too scanty
to decide whether spotting is due to a process of loss of the factor for uniformity
of pigmentation, or to a hypostatic restrictive factor. It seems, however, that
such spotting as one encounters in guinea-pigs, hooded rats, and in many mice
is a unit character subject to enormous quantitative fluctuation, and that it
may be considered due to a modification of the factor Y or U which is hypo-
static to unmodified or "self" forms.

In view of the fact that the same substance Y is distributed in two different
ways to produce spotting and dilution, we may consider it as consisting of an
amount of pigment (D) distributed over the entire animal (*S); therefore we
may consider the pigment of the wild mouse as being designated by the letters
DS. An animal may then be of one of the following formulae :

DS intense self. Ds intense spotted. dS dilute self, ds dilute spotted.

THE INHERITANCE OF SPOTTING. 41

We have previously discussed the observable fluctuations in amount of
pigment in animals possessing D, for example in yellows. The fluctuations
observed in the case of spotted animals are little if any greater in extent than the
fluctuations from deep orange to cream already noted in the case of yellow mice.
If there are two ways {d and s) in Avhich the factors D and S may respec-
tively be modified, we should expect that the same might hold in the case of the
factor P. The quantitative modification of this factor (p), acting upon brown
and black pigment to the exclusion of yellow, produces the pink-eyed colored
series.

If a regional modification of black and brown forming substances {Br and
B) existed, we should expect a spotted condition to be formed. Here, however,
the spots would be black or brown on a yellow ground. To such a class as this
we may say that the tortoise varieties of guinea-pigs belong. This condition
is in a measure hypostatic to self-pigmented forms, as are the (s) spotted forms.
We have supposed that the factor P produced a certain amount of black or
brown substance typified by the wild Mus musculus. This factor, then, ap-
pears to bear the same relation to the factors Br and B that the factor D does to
the factor Y. We may, therefore, logically construct a rough diagram to show
the relations of the distributive factors to Br and B, as we did in the case of Y:

Factors for the
production of
brown and
black pigment

D / Distributed in a certain f Modified in amount to form
^\ degree of depth = P \ pink-eyed varieties = p

n j Distributed to certain ( Modified in amount to form
'' \ extent (total) = T \ tortoise varieties = t

If we designate the tortoise spotting by t, we may consider its epistatic
allelomorph as T, total or self pigmentation. In this case the factor P becomes
comphcated, as did the factor D, becoming PT. As in the case of the factor
DS, animals may be of any one of the following formulae :

PT dark-eyed self. pT pink-eyed self.
Pt dark-eyed tortoise, pt pink-eyed tortoise.

In mice we find that the p modification has taken place, while in guinea-
pigs the t modification is well known, and Castle (19126) has described the origin
of a pink-eyed form of guinea-pig which may turn out to be the p modification.

It may be seen from the foregoing description that the two forms of
spotting (piebald and tortoise) are entirely independent, and it is thus entirely
conceivable that they should occur in the same individual. This appears to
be the case in the well-known tri-colored breeds of domesticated animals.

One of the best-known cases of inheritance in tri-colored races is found in
the case of "basset" hounds, on which Galton based his "law" of heredity.
The character considered was the presence or absence of black in addition to
yellow and white. When black was present the tri-color condition was pro-
duced. Though there is no direct evidence at hand, Bateson (1909), in dis-
cussing these experiments, states that yellow is not usually dominant to black.
If this is the case the observed facts may be explained as follows:

In guinea-pigs the presence of black and yellow spots on any individual
depends upon the presence of a spotting character which acts upon a totally

42 THE INHERITANCE OF COLOR IN MICE.

black pigmented animal to produce a blotched black-and-yellow appearance.
For the sake of convenience we may call animals possessing this "tortoise"
marking t. All self-black animals lacking this modification, and therefore
having no red blotches, are of the formula T. Experiments with guinea-pigs
(at present being carried on by Dr. Castle) shows that self-black is epistatic to
tortoise. This pair of characters is, however, independent from the factors,
E = extended black •pigmentation, necessary for the 'production of any black hairs
on the coat, and its allelomorph e =the loss of black pigment from the coat,
producing yellow animals.

Thus, if a race of tortoise animals existed, formula EEtt, we should have a
homozygous race of tortoise animals (which in fact exist) . If, however, the
tortoise animals were of the formula Eett we should expect young of three
kinds:

(a) EEtt tortoise. (6) Eett tortoise. (c) eett yellow.*

Types (a) and (6) having E present would be able to form black pigment on the
coat; but type (c), lacking E, would be yellow in appearance, though it would
be potentially tortoise.

If the factor for spotting with white (s) be added to the formula of a tor-
toise animal {Eett), we should have, if these animals were bred together, three
kinds of young.

(a) EEttss tri-color (tortoise and white).
(6) Eettss tri-color (tortoise and white),
(c) eettss yellow and white.*

Types (a) and (6) would be tri-color, that is, tortoise and white; type (c)
would be yellow and white. This might account for the appearance of yellow
and white individuals in a race of tri-colored animals.

If, however, yellow were epistatic to black, as in mice, we should have to
explain things differently. Tortoise animals could then be of only one formula
and would breed true, being recessives, whereas self yellows might also produce
tortoise young.

rrtt = tortoise.

Rrtt = yellow (heterozj^gous in tortoise).
RRtt = yellow (homozygous).

If, now, the modification s were added to such hypothetical tortoise
animals, we should have

rrttss = tri-color (tortoise and white) homozygous.

If such animals were crossed inter se, we should, on genetic grounds, have
to suppose a change of dominance to explain the occurrence of yellow-and-
white young. This does not seem likely. A simple mechanical fact is, how-
ever, able to account for the occurrence of yellow-and-white animals in an
homozygous or heterozygous race of tortoise-and-white (tri-color) animals.
Both forms of spotting are independent as to the regions of the coat which they
affect. If the white regions should, by chance, coincide with the black regions

*Castle (1905), p. 34, has described such animals.

CROSSES WITH JAPANESE WALTZING MICE.

43

of a tortoise animal we should have an animal yellow-and-white in appearance,
though gametically a pure tri-color (tortoise and white). This condition is
found in guinea-pigs where two yellow (red) and white animals when crossed
together have given young with black on the coat (Castle, 1912), and we know
that one of these animals at least must have the gametic composition of a tri-
color. In a case of this sort the yellow-and-white animals would occur in
ratios entirely free from any mendelian principle, and would give a spurious
reversal of dominance.

Perhaps one of the two foregoing suggestions may serve to throw some light
on the results upon which Galton's "law" of heredity was based. It must be
remembered that tortoise-shell animals are in their gametic composition no more
intermediates between black (extended) and yellow (restricted) animals than
forms spotted with white are intermediate between colored forms and albinos.

CROSSES WITH JAPANESE WALTZING MICE.

Morgan (1911a) has mentioned the fact that in crosses between self and
spotted forms, in mice, the spotting seemed modified or contaminated by the
cross. He gives no figures, however, in support of this statement and fails
to mention that the modification of spotted forms by crossing with self was
reported by MacCurdy and Castle (1907).

Dr. Castle and the writer have examined carefully the degree of pigmen-
tation of a race of pure Japanese spotted mice and have estimated the percent-
age of colored area on the dorsal surface; 72 animals were thus examined. The
average pigmentation was 32 per cent. The range of pigmentation was from
20 to 55 per cent. Animals of this pure Japanese race were crossed with a
uniform self-pigmented race of homozygous dilute brown animals, known to
produce no spotted or albino young. Fi from these animals consisted of all self
pigmented young showing no spots of white. Certain of these Fi animals were
crossed inter se to obtain F2, others were crossed back with females of the pure
Japanese race.

In the first case F2 was found to consist of 45 self animals (no spots) and 21
animals having some white hairs or spots on the dorsal surface. The 3 to 1
ratio is here approximated, the exact theoretical expectation being 49.5 self
to 16.5 spotted. The extracted spotted animals differ widely from the original
Japanese race from which they inherited the spotted-coat character. A com-
parison of the two categories of spotted forms (together with the back cross,
which will be treated later) will be seen in the following table :

No. of

spotted

individuals.

Average
percentage

of dorsal

surface

pigmented.

Range of in-
dividuals in
percentage
of dorsal
surface
pigmented.

(1) .Japanese

(2) F2

72
21
47
19

32
85.3
60.2
70.4

20 to 55
50 to 99
40 to 99
47 to So

(3) Back cross

(4) Back cross F2. ■ ■

44 THE INHERITANCE OF COLOR IN MICE.

From this table it will be seen that the spotted individuals of Fo have been
contaminated by the cross, having their dorsal pigmentation increased on the
average more than 50 per cent over the average of the pure Japanese race.
The range of the spotted forms in Fi is also very different from that in the
Japanese race. There are no F^ animals within 18 per cent of the average grade
of the Japanese mice (32 per cent); also there is only one F^ animal out of 21
that is as lightly pigmented as the darkest of the Japanese race.

The back cross, between Fi animals and individuals from the pure Jap-
anese race, we should expect to give spotted and self animals in a 1 : 1 ratio.
The spotted animals, on a basis of contamination, should not be so extensively
modified as in the F^ animals; that is, their degree of dorsal pigmentation
should be less. There have been 96 animals produced in this back cross, of
which 49 are self and 47 spotted, showing that "spotting" and ''self" are still
behaving as a pair of allelomorphic characters. The spotted animals from this
cross — see above table, (3) — show an average of 60.2 per cent of the dorsal
surface pigmented; their range is from 40 to 99 per cent. This coincides
qualitatively with the expectation.

One more cross may be recorded. Certain of the 49 selfs produced by the
back cross were bred inter se, thus producing a generation which may be desig-
nated as "back cross Fo." Spotted animals resulting from this cross, on the
theory of contamination, should show a degree of dorsal pigmentation between
that of the first Fo (85.3 per cent) and of the back cross (60.2 per cent). As a
matter of fact the results show that their average pigmentation is 70.4 per cent.

ASSOCIATION OF CHARACTERS.

The question naturally arises as to whether the various characters are
completely independent of each other or whether coupling or gametic associ-
ation of any sort exists between som.e of them. Morgan (19116) has observed
in Drosophila certain results best explained on an hypothesis of "association"
of certain characters in the gamete. It remains to be seen whether any such
"association" of characters exists in mice. For this purpose the writer has
tabulated the results of four crosses:

I. Cross 10a. Wild Black Agouti (Mus musculus) Crossed with Dilute Brown.

The black-agouti parent possesses factors B = black, A = agouti, and D =
density. The dilute-brown parent lacks the factors B, A, and D. Fi resem-
bles the wild parent. In F^ we expect 8 classes, as follows :

(1) Black agouti =BrBAD* (5) Brown =BrD

(2) Black =BrBD (6) Dilute brown agouti ='BrAd

(3) Brown agouti =BrAD (7) Dilute black =BrBd

(4) Dilute black agouti =BrBAd (8) Dilute brown =Brd

*A11 animals in this cross possess the general color factor Y, and the factor (or fidlness
of black and brown pigmentation, P. They are therefore omitted from the formula? for
purpose of simplification.

ASSOCIATION OF CHARACTERS.

45

On an hypothesis of association we should expect types (1) and (8) to be
in excess of the numbers called for by random segregation. The experimental
results are:

Observed .

Expected on a basis of
random segregation.

(1)

BAg.
20

(2)
Blk.

(3)
BrAg.

(4)
Dilute
BAg.

(o)
Brown.

(0)
Dilute
BrAg.

(7)

Dilute

Blk.

(8)

Dilute

Br.

9

7

9

0

4

4

2

23

7.7

.77

7.7

2.G

2,G

2.G

1.0

The sum of classes (1) and (8) on a basis of random segregation is 24. The
observed number is less by 2, showing no signs of association of the characters
A, B, and D.

II. Cross 10. Pink-Eyed Black Agouti Crossed with Dilute Brown Agouti.

The pink-eyed black agouti parent possesses B (black), D (density), and
lacks P (fullness of black and brown pigmentation, dark eye). The dilute
brown agouti parent is of the formula dP, lacking the factor for density but
possessing that for dark eye. Fi is indistinguishable from the wild black agouti

{Mus musculus).

Pink-eyed black agouti BrpBD x dilute-brown agouti BrPd.

Fi Black agouti, BBr^PpOd
Fi {I) Black agouti, BrBPDA

(2) Brown agouti, BrPDA

(3) Pink-eyed black agouti, BBrpDA

(4) Dilute black agouti, BrBPdA

Fi (5) Pink-eyed brown agouti, BrpDA

(6) Pink-eyed dilute-black agouti, BrBpdA

(7) Dilute-brown agouti, BrPdA

(8) Pink-eyed dilute-brown agouti, BrpdA

Classes (3) and (7) should be in excess if there is anj^ association. The
experimental results follow:

(1)
BAg.

(2)
BrAg.

13

13.5

(3)
pBag.

(4)
dBag.

(5)
pBrAg.

(6)
pdBag.

(7)
dBrag.

(8)
pdBrag.

Observed

40

40.5

12
13.5

18
13.5

3

4.5

3

4.5

5

4.5

2
1.5

Expected on a basis of
random segregation .

The sum of classes (3) and (7) on a basis of random segregation is 18, the
observed number in the classes is 17; again no evidence of association.

III. Cross 66. Pink-eyed Black Crossed with Brown.

The pink-eyed black parent possesses the factor B but lacks P and is there-
fore Bp; the brown parent lacks B but possesses P.

Parents black Bp x brown P.

Fi Black BPp. Fi (1) Black BP,
(2) Pink-eyed black Bp, (3) Brown P, (4) Pink-eyed brown p.

46

THE INHERITANCE OF COLOR IN MICE.

On a basis of association of characters both classes (2) and (3) should be
in excess. The observed result follows:

Classes.

(1)
Black.

199
199

(2)

Pink-eyed

black.

(3)
Brown.

. (4)
Pink-eyed
brown.

Observed

75
66.3

61
66.3

19
22.1

Expected on basis of random segregation

It will be seen that while type (2), pink-eyed black, is slightly in excess,
the browns (which must also on the association hypothesis be in excess) are not.
The sum of classes (2) and (3) is 136, while on the supposition of random segre-
gation we should expect 132.6.

IV. Cross 96. Brown Crossed with Pink-Eyed Dilute-Brown.

Brown possesses both factors D and P; pink-eyed dilute brown has neither
of them and is djp in formula.

Brown DP x Pink-eyed dilute broivn dp,

Fi Brown, DdPp. Fi (1) Brown, DP, (2) Dilute brown, dP,
(3) Pink-eyed brown, Dp, (4) Pink-eyed dilute brown, dp.

On an association hypothesis both classes (1) and (4) should be in excess.

Classes.

(1)
Brown.

Observed .

Expected on a basis of random seg-
regation

49

41.4

(2)

Dilute
brown.

21

13.8

(3)

Pink-eyed
brown.

13.8

. (4)
Pink-eyed

dilute

brown.

4.6

Sum of

classes (1)
and (4).

50

46

The sum of classes (1) and (4) is onlj^ 4 in excess of the expectation on a
basis of random segregation. This may be considered as showing no associ-
ation, because class (4) is not in excess of the expectation. If now we add
together the numbers of individuals observed in the classes that should show
"association," if it exists, we have 225, while the number called for by the
mendelian hypothesis of random segregation is 220.6, a striking approximation
to the observed numbers. We may then conclude that these experiments show
no sign of association in the gametes between the factors D, P, A, or B or
between the four conditions characteristic of their absence.

PART IL EXPERIMENTAL DATA.
EXPLANATION OF SYMBOLS.

Before giving in detail the matings made, a few general facts may be
stated. In the course of the experiments noted here, more than 10,500 animals
have been raised. The independence of all the factors given in this paper has
been made certain from breeding tests. The results may first be considered in
a general way which may serve, for the present, to show that the factors in-
cluded in this paper exist as units in inheritance. We may best consider the
yellow and non-yellow forms under different headings. For non-yellow mice,
the results given here are largely corroborative of evidence previously given by
Cuenot, Bateson, Durham, and other investigators.

In expressing the gametic or zygotic formuliie of the various types we
employ a slight modification of the two systems most frequently used. Thus,
when a given factor is known to be absent, its symbol is o/?2?7ferf from the formula.
For example, the gametic formula of homozygous brown-pigmented animals is
given as YBrDP, the zygotic formula Y-iBr^DiP^- Albinos, which are gameti-
cally homozygous brown animals, would differ merely in that the color pro-
ducer Y is absent; they would, therefore, have the gametic formula BrDP and
the zygotic formula Br^DoP-i. If the original brown race had been hetero-
zygous in the color factor Y, its zygotic formula would be YBriDoP^ and the
gpjnetes that could be formed would be obviously YBrDP and BrDP.

If, however, we are dealing with such a pair of characters as "dark-eye"
P and ''pink-eye" p, we are not justified in supposing an absence of P in the
pink-eyed forms. We merely know that an hypostatic modification of P has
occurred, and this is best designated by p. If now we have a homozygous
brown animal, with the zygotic formula l^/^r^Do-Po, we may designate the homo-
zygous pink-eyed brown as Y^BriDiPi. The dark-eyed brown heterozygous in
P would then be Y-iBriDiPj) and would form two sorts of gametes YBrDP and
YBrDp.

It is interesting to note that the system employed by the foremost expo-
nents of the presence-and-absence hypothesis really hints at the presence of two
conditions, the one (B) epistatic to the other (b). On the other hand. Castle, who
does not follow so implicitly the limits of the presence-and-absence h;j/pothesis,
adopts a system of notation which, in the case of certain characters, indicates
the hypostatic condition by the absence of any symbol to designate it.

The excellent comparative study by Cuenot (1911) has served to make

clear many debated points due to variations in systems of notation, and it is

therefore with some doubt as to its advisability that the writer advances still a

different one. It seems, however, exceeding present knowledge to denote by

the same system characters which may obviously be absent and those whose

absence is far from proved.

47

48

THE INHERITANCE OF COLOR IN MICE.

There should exist, according to the hypothesis advanced above, 81 types
of zygotes in the non-yellow self-colored races. A similar number of types of
albinos should also be formed. In the experiments here recorded no effort has
been made to obtain a large number of tj^pes of zygotes, yet 58 of the 81 pure
colored types have been met with. The occurrence of these 58 types is assured
by breeding tests, but it is almost certain that all 81 types have occurred many
times in the writer's experiments, since only a very small part of the animals
raised has been used for breeding.

A table follows showing the numbers of possible zygotic types, and the
number of the observed types in the 16 self-pigmented non-j^ellow color varie-
ties which are homozygous in the color-producer (F).

Gametic formula.

Description.

Possible.

Observed.

YBrBDPA

Black agouti

16

8

8

8
5
8
5
5
2
3
3
2
4
4
2
2
2
2
1

YBrBdPA

Dilute black agouti

YBrBDvA

Pink-ej^ed black agouti

YBrBDF

Black

8

YBrDPA

Brown agouti

8
4
4
4
4
4

4
o

YBrBdpA

Pink-eyed dilute black agouti

YBrDpA

Pink-eyed browTi agouti

YBrBDv

Pink-eyed black

YBrdPA

Dilute brov^Ti agouti

YBrDP

Brown

YBrBdP

Dilute black

YBrdP

Dilute brown

YBrDp

Pink-eyed brown

2
2

YBrdpA

Pink-eyed dilute brown agouti

YBrBdp

Pink-eyed dilute black

2

1

YBrdp

Pink-eyed dilute brown

81 58

If yellow animals differ from the non-yellow by the presence of an epi-
static restriction factor, R, we should expect that the 81 zygotic types of non-
yellow mice would have their counterpart in the yellow series. Cuenot (1911)
recognizes this fact, but explains it in a slightly different way, which need not
be discussed here.

Yellow animals corresponding with 14 of the 16 non-yellow color varieties
have been recognized in breeding tests. The yellows which arc potentially
dilute brown and those which are potentially pink-eyed dilute-brown agouti
are the only forms not as yet demonstrated by breeding tests. There is no
reason to suppose that these can not be produced, and it is almost certain that
they have occurred among my animals but have not happened to be chosen for
breeding.

The gametic and zygotic formulae used in this part of the paper will be
identical with those employed in the first part. A set of abbreviations, given
on p. 50, will be used in tables. The results here tabulated follow the various
experiments through April 15, 1912.

COLOR VARIETIES OF MICE.

49

COLOR VARIETIES OF MICE.*

A. Extended Series (Restriction Factor Absent).
1. With the agouti pattern.

Color variety.

1. Black agouti, fig. 1 YBrBDPA '

2. Dilute black agouti, fig. 2 YBrBdPA

3. Pink-eyed black agouti, fig. 3 YBrBDpA

4. Pink-eyed dilute black agouti, fig. 4 YBrBdpA

5. Brown agouti, fig. 5 YBrDPA

6. Dilute brown agouti, fig. 6 YBrdPA

7. Pink-eyed brown agouti, fig. 7 YBrDpA

8. Pink-eyed dilute brown agouti, fig. 8 YBrdpA

9.
10.
11.
12.

13.
14.
15.
16.

2. Without the agouti pattern.

Black, fig. 9 YBrBDP

Dilute black, fig. 10 YBrBdP

Pink-eyed black, fig. 11 YBrBDp

Pink-eyed dilute black, fig. 12 YBrBdp

Brown, fig. 13 YBrDP

Dilute brown, fig. 14 YBrdP

Pink-eyed bro\\Ti, fig. 15 YBrDp

Pink-eyed dilute brown, fig. 16 YBrdp

Black
agouti
series

Brown

agouti
series

Black
series

Brown
series

B. Restricted Series. Animals in this Series Always Heterozygous in R.

20
21
22
23
24

25
26

Color variety.

17. Black-eyed yellow YBrBDP AR

18. Black-eyed yellow, fig. 17 YBrBDPR

19. Brown-eyed yellow, fig. 18 YBrDPAR

Brown-eyed j'ellow YBrDPR

Dilute black-eyed yellow YBrBdPAR

Dilute black-eyed yellow YBrBdPR

Dilute brown-eyed yellow YBrdP AR

Dilute brown-eyed yellow, fig. 19 YBrdPR

Pink-eyed yellow YBrBDp AR f^^^^^^-' ^^^^^1

Pink-eyed yellow YBrBDpR

Dark-eyed
intense yel-
low series

Dark-eyed
dilute yel-
low series

27. Pink-eyed yellow YBrDpAR

28. Pink-eyed yellow YBrDpR

29. Pink-eyed dilute yellow YBrBdpAR

30. Pink-eyed dilute yellow YBrBdpR

31. Pink-eyed dilute yellow YBrdp AR

32. Pink-eyed dilute yellow YBrdpR

and yellow

pigment. I • . - i

T> „ „ „, ^ u intense yel-

Brown and , ••'

yellow pig-
ment only

[Black, brown
and yellow
pigment

fBrown and
yellow pig-
ment only

Pink-eyed
intense ye"
low series

Pink-eyed
dilute yellow
series

There are 32 pigmented varieties of mice which may be obtained in pure
races. The "restricted series," however, may be obtained pure in the sense
only that animals may be obtained which give merely the type of yellow
written before their gametic formula, and the single variety of the "extended"
series which the rest of their gametic constitution demands. Albino varieties
corresponding with these 32 colored forms are expected to occur and may be
produced at will. These albinos are distinguishable from one another only by
breeding tests, and it is therefore doubtful whether all the 32 varieties have
as yet been isolated.

* The factors T (total pigmentation) and S (self-pigmentation) are not included in these
formulae.

50

THE INHERITANCE OF COLOR IN MICE.

In the following pages will be found a brief description of the various color
varieties, as they appear to the unaided eye, followed by a list of crosses made
with each color variety. In the tables it has been found expedient to use the
following abbreviations to designate in simpler form the color varieties, a list of
which has alread.y been given:

B = black,
Br = brown,

d = dilute.

}) = pink-eyed,

^1^ = agouti,

W = white (albino),

Y = yellow,
sY= sooty yellow,
cF = cream yellow.

Thus, for GXixm\Ae,pdBAg is equivalent to pink-eyed dilute black agouti, color
variety No. 4 of the extended series.

Unfortunately, in many of the crosses the numbers of animals recorded
are small. Aberrations from the expected mendelian ratios of the color
classes may also ]je found in some cases; but an examination of these seems
to indicate that they would diminish with an increase in the number of animals
recorded.

EXTENDED SERIES.

I. Black Agouti, YBrBDPA (Fig. 1).

The common coloration seen in tlie liouse-mouse {Mus musculus). Ej-es black, ears darkly
pigmented, hairs on ^-entral surface tipped with dull-yellowish, then dark slaty to the
base. Tail dark-pigmented. Dorsal hairs tipped with black, then having a yellow
band and below that being slaty to their base. Such an arrangement produces the
"ticked" or "agouti" coat pattern. Tuft of hairs at the base of the ears yellowish —
a few light hairs on sides, flanks, and feet. Hairs around anus are light.

Black agouti x Mack agouti.

Cross 1. Giving only BAg young; therefore one of the parents, at least, may be considered
homozygous black agouti, type 1 (extended series). The animals used in this cross
were descended from yellows.

Mating.

Parents.

BAg.

74
64

82
44
48

166 or 131 X 135

166 X 135

6

2

9

11

8

36

164 or 131 X uraiiarked.

139 X 530.()4/J

509.4C X 530.07/i

Cross 2.^ Parents heterozygous in black. YiBr-2BD'J'-2A2X YnBriBDiPxAi. Expectation,
3 BAg to 1 BrAg.

Mating.
561

Parents.

BAg.

BrAg.

4914 or 4915 x 4913 . . .

7

2

EXTENDED SERIES.

51

Cross 3. Parents heterozygous in color factor and in black. YBriBDiPiAixYBriBDiP^Ai.
Expectation, 9 BAg, 3 BrAg, to 4 W. The parents in this cross were derived from
yellows.

Mating.

Parents.

BAg. BrAg. W.

i

4o

530.022^X176

[ i
5 i 5 2

i

Cross 4. Parents heterozygous in black and density. YiBnBDdPiAt xYiBr-iBDdPiAz.
Expectation, 9 BAg, 3 BrAg, 3 dBAg, 1 dBrAg.

Mating.

Parents.

BAg.

BrAg. \ dBAg. (JBrAg.

25

530.6A X530.5A ...

9

1 !

4 1 1

Cross 5. Parents heterozygous in dark eye. YiBr2BiD2PpAi xYiBriB^DiPpAo.. Expec-
tation, ?, BAg to 1 vBAg.

Mating.

Parents.

BAg. pBAg.

134

138

673 X 671 ...
672 X 671 . . .

8
10

2
1

18

3

Cross 6. Parents heterozygous in color factor, dark eye, and agouti. YBriB-DiPpAx
YBriBiDJ'pA. Expectation, 27 BAg, 9 5, 9 pBAg, 3 pB, 10 W.

Mating.

Parents.

BAg.

pB.

W.

404

2889 X unmarked

2

1

1

Cross 7. Parents heterozygous in black, dark eye, and agouti. YiBriBDiPpA x YBriBD2PpA .
Expectation, 27 BAg, 9 pBAg, 9 BrAg, 9B,3 pBrAg, 3 Br, 3 pB, 1 pBr.

Mating.

Parents.

163
119
175
116
140
162
169

545 X 546

547 X 546

548 X 546

545 or 548 X 546 . . .
545-547-548 x 546. .

672-673 X 918

917x918

BAg.

BrAg.

B.

5

5

3

5

1

2

7

3

2

6

3

2

16

6

1

5

1

4

! 48

i

18

11

pBAg.

1
o

pBrAg.

Br.

pB I pBr.

1
2
1
2

1
2

9 4

52

THE INHERITANCE OF COLOR IN MICE.

Cross 8. Parents heterozygous in color factor, density, and dark eye. YBnBiDdPpAi x
YBriB^DdPpAi. Should give 27 BAg, 9 dBAg, 9 pBAg, 3 pdBAg, 16 W.

Mating.

Parents.

BAg.

dBAg.

pBAg.

pdBAg.l W.

340
462

2756, 2760 x 2757 ....
3120 x unmarked

2
3

2
2

1

1— (

5

4

1 1 1

Cross 9. Parents heterozygous in density, dark eye, and agouti. YiBriBiDdPpAx
YiBriBiDdPpA . Expectation, 27 BAg, 9 pBAg, 9 B, 9 dBAg, 3 pdBAg, 3 dB, 3 pB, 1 pdB.

Mating.

Parents.

BAg.

dBAg.

B.

pBAg.

pB.

pdBAg.

dB.

pdB.

403

Unmarked x unmarked . .

9

5

9

1

2

Cross 10. Parents heterozygous in black, density, and dark eye. Y2Br2BDdPpA2 x
YiBriBDdPpAi. Expectation, 27 BAg, 9 pBAg,^BrAg, 9 dBAg, 3 pdBAg, 3 pBrAg,
3 dBrAg, 1 pdBrAg.

Mating.

Parents.

BAg.

dBAg.

pBAg.

BrAg.

dBrAg.

pdBAg.

pBrAg.

pdBrAg.

P-?
1

?

338

1290 X 1289

9

1

2

2

1

199

1291 X 1289

5

7

3

4

1

1

1

203

1293 X 1289

2

1

3

2

241

1291 - 1293

i

X 1289 . .

3

3

, ,

1

1

1

275

1290-1291,

1293 X 1289

17

4

5

2

1

2

! 1

1

1

260

1539 X 1289

4

2

1

2

2

3

40

18

12

13

5

3

3

2

4

3

Cross 10a. Parents heterozygous in black, density, and agouti YiBriBDdPoA x YiBr^BDdPxA .
Expectation, 27 BAg, 9 dBAg, 9 BrAg, 9 5, 3 d5r.4s?, 3 dB, 3 Br, 1 dBr.

Mating.

Parents.

BAg. dBAg.

BrAg. B.

dBrAg.

dB \ Br. dBr.

A 2
A 7
A 8
A 10

56 X 55x58.

519 X 58

518 X 58

598 X 55

7

10

3

3
6

4 3

2 4

1 1

1

2
1

1

1
2 .'.■
2 \ '.'.

1
1

20

9

7 ' 9 4 1 4 i 0 ! 2

Black agouti x di7M<e btoc/; agouti.

Cross 11. Giving only BAg young, both parents homozygous. Y^BriB^D-iPiAzX
YiBroBidiPoAi.

Mating.

Parents.

BAg.

67

131x135..

8

EXTENDED SERIES.

53

Cross 11a. Black agouti heterozj'gous in black, density, and agouti crossed with dilute
black agouti heterozygous in black and agouti. YiBriEDdP^A x YiBriBdiP-iA.
Expectation, 9 BAg, 9 dBAg, 3 BrAg, 3 dBrAg, ZB,?, dB, 1 Br, 1 dBr.

Mating.

Parents.

BAg.

dBAg.

BrAg.

B.

All

,S105 X *S5 .

3

1 1

1

Cross 12. Black agouti, heterozygous in color factor, black, dark eye, and agouti, crossed
with dilute black agouti heterozygous in color factor, black, dark eye, and agouti.
YBriBDiPpA x YBr^BdiPpA. Expectation, ^IBAg, 21 B, 27 vBAg, 21 BrAg, 9 Br,
9 pB, 9 pBrAg, 3 pBr, 64 W.

Mating.

Parents.

BAg.

BrAg.

B.

pBAg.

pB.

Br.

pBrAg.

pBr.

W.
5

422

3405 X 3404

1

3

5

5 1

I

Black agouti x brown agouti.

Cross 13. Black agouti, heterozygous in black and density, crossed with brown agouti hetero-
zygous in density. YiBriBDdPiA-^. X YiBriDdPoAo. Expectation, 3 BAg, 3 BrAg,
1 dBAg, 1 dBrAg.

Mating.

Parents.

BAg.

BrAg.

dBAg.

dBrAg.
2

i

507
374
464

Unmarked x 3114

3116 X unmarked

Unmarked X 3114-3115...

1
3
6

3
1

7

1

1
1

10

11

3

3

Black agouti x black.

Cross 14. Black agouti heterozygous in the color factor crossed with black heterozygous in
the color factor. YBr^BiDiP-Ai x YBrzBiDiPi. Expectation, 3 BAg, 1 W.

Mating.

Parents.

BAg.

W.

410 Unmarked x unmarked ....

5

1

Cross 15. Black agouti heterozygous in agouti crossed with homozygous black.
YiBriBiDzPiA x YiBnB.D^P^. Expectation, 1 BAg, 1 B.

Mating.

Parents.

BAg.

B.

576
A 5
A13

7215x7216

S59 X 554

5'59 X 55

2
8
1

5
4

1

11

10

54

THE INHERITANCE OF COLOR IN MICE.

Cross 1 G. Black agouti heterozygous in dark eye and agouti crossed with black heterozygous
in dark eye. YiBriB-iDiPpA x YiBriBiD^Pp. Expectation, ZBAg,ZB,\ pBAg, 1 pB.

Matins

Parents.

BAg. B.

132
128
129
97
179
165
177

447 X 454 |. 1

449 X 454 ! 3

452 X 4.54

447, 449 X 454

447-449-452 x 454

447 X 919

452 X 919

3
2

19 20

pBAg. ' pB.

2
1
1

I 1

6

Cross 17. Black agouti heterozygous in black, dark eye, and agouti, crossed withblack hete-
rozygous in black and dark eye. YiBr^BDiPpA •xYiBroBD2Pp. Expectation, 9.6.4^,
9 jB, 3 pBAg, 3 pB, 3 BrAg, 3 Br, 1 pBrAg, 1 pBr.

Mating.

Parents.

BAg.

B.

vBAg.

BrAg.

Br.

pBrAg.

pB.

pBr.

130
107
335
324

551 X 553

551 X 671

2461 X 2122 ....
2460 X 2122 ....

1

3

5

'3

4
4

6

1

2

1

1

'3

1

1

1

1

2

9

11

9

1

5

2

1

2

Cross 17a. Black agouti heterozygous in black, density, and agouti, crossed with black
heterozygous in density and black. YiBriBDdPiA xYiBrJiDdPi. Expectation,
9 BAg, 9 £, 3 dBAg, 3 dB, 3 BrAg, 3 Br, 1 dBrAg, 1 dBr.

Mating.

Parents.

BAg.

B.

BrAg.

Br.

dBAg.

dBrAg.

dB.

dBr.

.46

56 X 535 . . .

2

5

3

2

1

1

1

Black agouti x brown.

Cross 18. Black agouti heterozygous in black crossed with homozygous brown.
Y2Br2BD2P2A2 xY2Br2D2P2. Expectation, 1 BAg, 1 BrAg.

Mating.

Parents.

BAg. BrAg.

526

5943 X 4920 ....

3 3

1

Cross 18a. Black agouti heterozygous in black and agouti crossed with homozygous brown.
Y2Br2BD2PiA xY2Br2D2P2. Expectation, 1 BAg, 1 BrAg, 1 B, 1 Br.

Mating.

Parents.

BAg.

BrAg.

B.

Br.

.414

56 X5/2-3001 ....

2

1 2

EXTENDED SERIES.

55

Cross 19. Black agouti heterozygous in color factor, black, and agouti crossed with brown
heterozygous in the color factor. YBr^EDxPiA xYBriD-iPn. Expectation, ZBAg,
3 £, 3 BrAg, 3 Br, 4 W.

Mating.

Parents.

BAg.

BrAg.

B.

Br.

W.

401

3306 X 3307

7

1

2

1

5

Black agouti x dilute brown.

Cross 20. Black agouti heterozygous in color factor, black, and density crossed.with dilute
brown heterozygous in color factor. YBriBDdPiAt x YBridiPi. Expectation, 3 BAg,
3 dBAg, 3 BrAg, 3 dBrAg, 4 W.

Mating.

Parents.

BAg.

(IBAg.

BrAg.

dBrAg.

W.

559

-25X-89

1

2

2

1

1

Cross 20a. Homozj^gous black agouti x homozygous dilute brown.

YiBr2B2D2P2A2 xY^Br^diPi. Expectation, all BAg.

Mating.

Parents.

BAg.

.41

S2xS\...

8

Cross 20b. Black agouti heterozygous in black and density crossed with homozygous dilute
brown. YiBrSDdPiAi x YiBr^diPt. Expectation, 1 5^^, 1 dBAg, 1 BrAg,^\ dBrAg.

Mating.

Parents.

BAg.

BrAg.

dBAg.

dBrAg.

.412
^15

309 xi?Z2X 3012.
381 xM2X3012.

2
1

2

2
2

3

2

4

Cross 20c. Black agouti heterozygous in black, density, and agouti crossed with homozy-
gous dilute brown. Y2Br2BDdPiA x Y2Br2d2P2. Expectation, 1 BAg, 1 BrAg, 1 dBAg,
1 B, 1 dBrAg, 1 Br, 1 dB, 1 dBr.

Mating.

Parents.

BAg.

BrAg.

B.

dBAg.

dBrAg.

Br.

dB.

dBr.

A-
.44
AQ

373-374 X 55 . . .

,S6xdil. 5r

<S62 X *S5

2
1
1

2
1

1

4

1

1
1

1

1

3 1

1 2

1

2
V

4

4

5

3

5

3

1 3

56

THE INHERITANCE OF COLOR IN MICE.

Black agouti x pink-eyed brown.

Cross 21. Black agouti heterozygous in dark eye and agouti, crossed with homozygous pink-
eyed brown. YiBriBiDiPpA x YiBriDiPi. Expectation, 1 BAg, 1 pBAg, 1B,1 pB.

Mating.

Parents.

BAg. pBAg.

B.

pB.

398

3305xp3309. . .

3 7

3

6

Black agouti x pink-eyed dilute broivn.

Cross 21a. Homozygous black agouti crossed with homozygous pink-eyed dilute brown.
YiBr^BiDiPzAi x YiBri/iiPi. Expectation, all BAg.

Mating.

Parents.

BAg.

626
630
633

p. dil. Br. X Vermont BAg .

7854 X Vermont BAg .

7855 X Vermont BAg .

26
9

7

42

Cross 21b. Black agouti heterozygous in black, density, and agouti crossed with homozy-
gous pink-eyed dilute brown. YiBr-iBDdPiA x Y^Bridip^. Expectation, 1 BAg,
1 BrAg, IB, I dBAg, 1 dBrAg, 1 Br, 1 dB, 1 dBr.

Mating.

Parents.

BAg.

BrAg.

B.

dBAg.

dBrAg.

Br.

dB.

dBr.
1

A3

599

Unmarked x S5

3

1

1

2

1

3
1

1
3

3
1

2,

Unmarked x unmarked . . .

4

1

3 4

4 1 4

2

1

II. Dilute Black Agouti, YBrBdPA (Fig. 2).

Eyes black, ears moderately pigmented, ventral hairs light slate colored with a yellowish
tinge. Tail moderately pigmented. Dorsal hairs showing the "agouti" pattern dis-
tinctly but somewhat faded, or washed out in appearance. Tuft of hght hairs present
at base of the ears and around the anus.

Dilute black agouti x dilute black agouti.
Cross 22. Both parents homozygous. Y2BriBi!d2P2Ai. Expectation, all dBAg.

Mating.

Parents.

dBAg.

621

7477 X unmarked . . .

12

Cross 22a. Both parents heterozygous in black, dark eye, and agouti. YiBrtBdiPpA.
Expectation, 27 dBAg, 9 dB, 9 pdBAg, 9 dBrAg, 3 dBr, 3 pdB, 3 pdBrAg, 1 pdBr.

Mating.

Parents.

dBAg.

dBrAg.

dB.

pdBAg.

pdBrAg.

pdB.

dBr.

pBr.

629
642

7695x7690-91-92..
7694 X 7690

9

2

1

1

1
2

1
1

1

1

1

9

2

2

3

2

1

1

0

EXTENDED SERIES.

57

Dilute black agouti x black.

Cross 22b. Dilute black agouti heterozygous in agouti crossed with homozygous black.
YiBriBAPiA xYiBnB^DiPi. Expectation, 1 BAg, 1 B.

Mating.

Parents.

BAg.

B.

562

6406 X 5881 . . .

5

6

Dilute black agouti x pink-eyed black.
Cross 23. Both parents homozygous. Y2Br2B2d2P2A2 xY2Br2B2D2P2. Expectation, all B^(7.

Mating.

Parents.

BAg.

8

323

p845xl871....

Cross 24. Dilute black agouti heterozygous in black, dark eye, and agouti crossed with
pink-eyed black heterozygous in black. Y2Br2Bd2PpA xY2Br2BD2p2. Expectation,
3 BAg, SB, 3 pBAg, 3 pB, 1 BrAg, 1 Br, 1 pBrAg, 1 pBr.

Mating.

Parents.

BAg.

B.

BrAg.

Br.

pBAg.

pB.

pBrAg.

pBr.

372

p2688x2488...

1

3

1

1

4

Dilute black agouti x pink-eyed dilute black.
Cross 25. Both parents homozygous. F2Br2B2C?2P2^2 xF2-Br2B2d2P2. Expectation, all dB.A{7.

Mating.

Parents.

dBAg.

416

p3627 X unmarked ....

5

Dilute black agouti x pink-eyed black agouti.
Cross 26. Dilute black agouti heterozygous in dark eye, crossed with pink-eyed black
agouti heterozygous in density. Y2Br2B2d2PpA2 X Y2Br2B2Ddp2A2. Expectation,
1 BAg, 1 pBAg, 1 dBAg, 1 pdBAg.

Mating.

Parents.

BAg.

pBAg. dBAg.

pdBAg.

368

2255xpl775..

1

1

Dilute black agouti x pink-eyed dilute black agouti.

Cross 27. DUute black agouti heterozygous in dark eye crossed with homozygous pink-
eyed dilute black agouti. Y2Br2B2d2PpA2 x Y2Br2B2d2P2A2. Expectation, 1 dBAg,
1 pdBAg.

Mating.

Parents.

dBAg.

pdBAg.

522

386

p unmarked x unmarked . .
2254xp2339

3
1

2
4

560

p4060x4244

2

6

6

58

THE INHERITANCE OF COLOR IN MICE.

Dilute black agouti x brown.

Cross 28. Dilute black agouti heterozygous in agouti crossed with homozygous brown.
Y^Br^BidnPiA x Y^Br^DiPi. Expectation, 1 BAg, 1 B.

Mating.

Parents.

BAg.

227 Unmarked x unmarked

B.

Dilute black agouti x pink-eyed dilute brown.
Cross 2Sa. Both parents homozygous. Y iBriBidtPiAi x F2Br2C?2P2. Expectation, all dBAg.

Mating.

Parents.

dBAg.

586
610
615
613

Unmarked x unmarked..
7477 x 7476

7

8

8

11

7545 X 7503

Unmarked x unmarked..

34

Cross 28b. Dilute black agouti heterozygous in agouti crossed with homozygous pink-eyed
dilute brown. Y2Br2B2d2P2A x F2fi?'2C?2P2. Expectation, 1 dBAg, 1 dB.

Mating.

Parents.

dBAg.

dB.

598
617

Unmarked x unmarked . . .
Unmarked x unmarked . . .

4
4

3

2

8

5

Cross 28c. Dilute black agouti heterozygous in black crossed with homozygous pink-eyed
dilute brown. Y2Br2Bd2P2A2 X Y2Br2d2pz- Expectation, 1 dBAg, 1 dBrAg.

Mating.

Parents.

dBAg.

dBrAg.

585

Unmarked x unmarked . . .

4

4

Cross 2Sd. Dilute black agouti heterozygous in black and agouti, crossed with homozygous
pink-eyed dilute brown. Y2Br2Bd2PtA x YiBr^dopi. Expectation, 1 dBAg, 1 dB,
1 dBrAg, 1 dBr.

Mating.

Parents.

dBAg.

dB.

dBrAg.

dBr.

591

Unmarked x unmarked ....

3

1

EXTENDED SERIES.

59

III. Pink-eyed Black Agouti, YBBrDpA (Fig. 3).

Eyes very deep pink. Ears apparently unpigmented. Hairs on ventral surface dull yellow
with bluish base, showing the presence of the agouti pattern. Dorsal hair closely
resembling that of the dark-eyed brown agouti form to the unaided eye. More yellow,
however, seems to be present in the coat, though it has been seen that this is not
because of an increased amount of yellow pigment. There is a tuft of light hairs at
the base of the ears. The hairs directly around tlie anus, however, resemble the other
ventral hairs so closely as to be indistinguishable from them.

Pinlc-eycd black agouti x pink-eyed black agouti.

Cross 29. One or both parents homozygous. YiBr^BiD-zPiAi x YoBrSiDiPiAi
tation, all pBAg.

Expec-

INIating.

112
1.36
153
139
190

Parents.

pBAg.

500 X 559

15

5
10
15

090 X 091

689 X 091

692 X 091

090-092x091

58

Cross 30. Both parents heterozygous in black. YoBrnBDypzAi x YiBriBDipiAi. Expecta-
tion, 3 pBAg, 1 pBrAg.

Mating.

120
101

Parents.

pBAg.

pBrAg.

558 X 559

19
3

1

4

558 or 500 x 559

22

5

Cross 31. Both parents heterozygous in black, density, and agouti. Y^BrtBOdpiA x
YiBfiBDdpiA. Expectation, 27 pBAg, 9 pdBAg, 9 pBrAg, 9 pB, 3 pdB, 3 pdBrAg,
3 pBr, 1 pdBr.

Mating.

Parents.

pBAg.

pdBAg.

pBrAg.

pB.

pdBrAg.

pdB.

pBr.

pdBr.

300

2018x2017....

17

2

0

3

Pink-eyed black agouti x black.
Cross 32. Pink-eyed black agouti heterozygous in agouti crossed with homozygous black.
Y^BnBnDiPiA xYiBrzBiDiPi. Expectation, 1 BAg, 1 B.

Mating.

Parents.

BAg.

B.

152

83

410xp409

103xp412

1
2

2
3

3

5

60

THE INHERITANCE OF COLOR IN MICE.

Pink-eyed black agouli x pink-eyed black.
Cross 33. Both parents homozygous. YiBriBiDiPiAiXY^BriB-iDiPi. Expectation, all pB.4^.

Mating.

Parents.

pBAg.

171
174

pl049xp898

p985 X p898

4
4

8

Cross 34. Pink-eyed black agouti heterozygous in black and agouti crossed with pink-eyed
black heterozygous in black. Y2Br2BDiPiA x YiBr-iBD^Pi. Expectation, 3 pBAg,
3 pBrAg, 1 pB, 1 pBr.

Mating.

Parents.

pBAg. pB.

pBrAg.

pBr.

84

7>408xp412...

2

2

1

Pink-eyed black agouti x dilute black.

Cross 35. Pink-eyed black agouti heterozygous in density crossed with dilute black hetero-
zygous in dark eye. Y-zBriBoDdpiA-i xY^BriBidiPp. Expectation, 1 BAg, 1 dBAg,
1 pBAg, 1 pdBAg.

Mating.

Parents.

BAg. dBAg.

pBAg.

pdBAg.

413

3062x7)1922....

4 7

7

Pink-eyed black agouti x dilute brown agouti.

Cross 36. Both parents homozygous. YiBriB2D2PiAi x Y2Br2d2P2A2. Expectation,
BAg only.

Mating.

Parents.
682 X p691 . . .

BAg.
15

148

Cross 37. Homozygous pink-eyed black agouti crossed with dilute brown agouti hetero-
zygous in dark eye. F2J5r2^2/)2PiA2 X Y2Br2d2PpA2. Expectation, 1 BAg, 1 pBAg.

Mating.

Parents.

BAg.

pBAg.

387

p unmarked X 1873

4

2

Cross 38. Pink-eyed black agouti heterozygous in density and agouti crossed with dilute
brown agouti heterozygous in agouti. Y2Br2B2Ddp2A x Y2Br2d2PzA. Expectation,
ZBAg,^ dBAg, 1 B, 1 dB.

Mating.

Parents.

BAg.

dBAg.

B. dB.

506

pl441 X4608..

6

3

1

1

EXTENDED SERIES.

61

Cross 39. Pink-eyed black agouti heterozygous in black and density crossed with dilute
brown agouti heterozygous in dark eye. YiBrzBDdp^Ai X Y2Br2d2PpA2. Expecta-
tion, 1 BAg, 1 pBAg, 1 dBAg, 1 BrAg, 1 pBrAg, 1 dBrAg, 1 pdBAg, 1 pdBrAg.

Mating.

Parents.

BAg.

pBAg.

dBAg.

BrAg.

pBrAg.

dBrAg.

pdBAg. pdBrAg.

369
302
344

punmarked x 1873. . .
pl923-pl874xl873..
pl875xl873

10

13

1

15

1
4

5

2
2

5

4

1

24

15

5

9

5

4

1

Pink-eyed black agouti x brown.
Cross 40. Both parents homozygous. Y2Br2B2D2P2A2 x Y2Br2D2P2. Expectation, only 5^ ff.

Mating.

Parents.

BAg.

252
187
286
202
223
198
207
206
235

pl416xl561

pll25xl527

?;15.33xl40o

?}1396 X unmarked..
7>1368 X unmarked..
pl297 X unmarked..

1403x^1099

572xpl099

1403 X p691

5

4
8
8
5

1

6
16

59

Cross 41. Pink-eyed black agouti heterozygous in agouti crossed with homozygous brown.
Y2Br2B2D2ViA x Y2Br2D2P2- Expectation, 1 BAg, 1 B.

Mating.

Parents.

BAg.

B.

249
228
219
279
193
209
213
161
239
227

7>1326 X 1674

2
14
8
3
1
2
3
1
4
3

1

10

3

1
2
2

2

3
3
1

7)1062 X 1674

»1060 X 1674

pl328 X 1561

yll48xl527

1)1330 X 1404

1570 X 531120

646 X pioei

1488 X 73844

Unmarked x unmarked . .

41

28

Cross 42. Pink-eyed black agouti heterozygous in black and agouti crossed with homozy-
gous brown. YoBr2BD2P2A xY2Br2D2P2. Expectation, 1 BAg, 1 B,l BrAg, 1 Br.

Mating.

Parents.

BAg.

B.

BrAg.

Br.

253
332

pl443xl405..
pl972 X 2071 . .

4

1

2

1
2

2

4

3

3

2

62

THE INHERITANCE OF COLOR IN MICE.

Cros3 43. Pinlv-eyed black agouti heterozygous in agouti crossed with brown heterozygous
in dark eye. YiBnB-iDiPiA x YiBriDzPp. Expectation, 1 BAg, IB, I pBAg, 1 pB .

Mating.

Parents.

BAg. pBAg.

i

B. \ pB.

182
181
231

1097x1526...
1098x1526.. .
1125x1526.. .

1
14

2

11

1

1

1 1 1

17

12

1

2

Cross 44. Pink-eyed black agouti heterozygous in density crossed with brown heterozygous
in density. YJir^.B'iDdpiAi X Y-iBrzDdP-i. Expectation, 3 BAg, 1 dBAg.

Mating.

Parents.

BAg.

dBAg.

298

2179 x 1922. . .

4

2

Cross 45. Pink-eyed black agouti heterozygous in black, density, and agouti crossed with
brown heterozygous in density. YoBriBDdp^A x Y-iBriDdPz. Expectation, 3 BAg,
3 BrAg, 3 5, 3 Br, 1 dBAg, 1 dBrAg, 1 dB, 1 dBr.

Mating.

Parents.

BAg.

BrAg. \ B.

Br.

dBAg.

1

dBrAg. dB.

1

dBr.

229

1710x1405...

6

4

1

1

Cross 46. Pink-eyed black agouti hetei-ozygous in density and agouti, crossed with brown
heterozygous in density. YzBriBoDdpiA x YiBriDdPi. E.xpectation, 3 BAg, 3 B,
1 dBAg, 1 dB.

Mating.

Parents.

BAg.

5
3
1

dBAg.

B.

dB.

317
221
291

1326x1404

1332x1404

1326-32x1404..

2
2

4
4

2
1

9 4

1

8

3

IV. Pink-eyed Dilute Black Agouti, YBBrdpA (Fig. 4).

Eyes pink; ears, feet, and tail apparently unpigmented. The color of the coat is markedly
washed-out in quaUty. The agouti pattern is distinguishable, but not easily so, because
of the "streaky " due to the absence of intense pigmentation. The whole coat resembles
a Uttle that of a very Ught dilute dark-eyed brown agouti. The ear tufts of yellowish
hair are prominent. There are no crosses to be included under this variety, though
some in which one parent is pink-eyed dilute black agouti have been recorded under the
preceding varieties.

V. Brown Agouti, YBrDPA (Fig. 5).

Eyes a deep rich brown, ears brown pigmented. Hairs on ventral surface yellowish on tip,
dull brown at base. Tail brown pigmented. Dorsal hairs brown at the tip, then a
yellow band, and finally dull brown to the base, giving the unmistakable "ticked" or
"agouti" coat. Whiskers and feet are brown. Light hairs around the anus and at the
base of the ears.

EXTENDED SERIES.

63

Brown agouti x brown agouti.

Cross 47. One or both parents homozygous. Y2Br2D2P2A2 x Y2Br2DtP2A2. Expectation,
all brown agouti.

Mating.

Parents.

BrAg.

124

86

143

414

651 x272

6

18

6

7

367x272

281 x272

Unmarked x unmarked

37

Cross 48. Both parents heterozygous in agouti. Y2Br2D2P2A x Y2Br2T>2P2A. Expecta-
tion, "iBrAg, 1 Br.

1

Mating. Parents.

BrAg. Br.

104 , 586x588

'

1

Cross 49. Both parents heterozygous in density and the color factor. FSrzDdP^Aj x
YBriDdPiAi. Expectation, 9 BrAg, 3 dBrAg, 4 W.

Mating.

Parents.

BrAg.

dBrAg.

W.

89

511. lA x411.

3

2

2

Cross 49a. Both parents heterozygous in density, dark eye, and agouti. Y2Br2DdPpA.
Expectation, 27 BrAg, 9 dBrAg, 9 pBrAg, 9 Br, 3 pBr, 3 pdBrAg, 3 dBr, 1 pdBr.

Mating.

Parents.

BrAg.

dBrAg.

pBrAg.

Br.

dBr.

pBr.

pdBrAg.

pdBr.

631
643
644

7679x7678-80....

7663 X 7660

7664x7662

6
2
2

1
1

2

1

1
1

3

• •

10

4

3

3

Brown agouti x pink-eyed brown agouti.
Cross 50. Brown agouti heterozygous in dark-eye, color factor, and agouti crossed with
pink-eyed brown agouti heterozygous in the color factor and agouti. YBr2D2PpA x
YBriDiPiA. Expectation, 9 BrAg, 9 pBrAg, 3 Br, 3 pBr, 8 W.

Mating.

Parents.

BrAg.

Br.

pBrAg.

pBr.

W.

407
365

p unmarked x 2735 . . . .
»2137 X 2735

8

4
1

2
2

2

2

3
1
1

350

»2138 X 2735

1

8

6

6

2

5

64

THE INHERITANCE OF COLOR IN MICE.

Brown agouti x brown.

Cross 51. Homozygous brown agouti crossed with homozygous brown. Y2Br>D>P2A2 x
YiBriD-iPi. Expectation, all BrAg.

Mating.
96

Parents.

BrAg.

488 X 162 . . .

G

Cnoss 52. Brown agouti heterozygous in dark e3'e and agouti crossed with brown heterozy-
gous in dark eye. YiBrJ^iPpA xY^Br'D'Pp. Expectation, 3 BrAg, 3 Br, 1 pBrAg,
1 pBr.

Mating.

Parents.

BrAg.

Br.

pBrAg.

pBr.

405
305
347

Unmarked x unmarked.
2129x2130

4

3

9
6

1

5
4

-2
3

Unmarked X 2130

10 18 10

5

Brown agouti x pink-eyed broivn.
Cross 53. Both parents homozygous. YiBr-iDiPiAt x YiBriDiPi. Expectation, all BrAg.

Mating.

Parents.

BrAg.

359

i

p2309x2131..

4

Brown agouti x dilute black.

Cross 54. Brown agouti lieterozygous in densitj' and agouti, crossed with dilute black
heterozygous in black. Y-iBr-iDdP-iA x YiBriBd^Pz. Expectation, 1 BAg, 1 dBAg,
1B,1 (IB, 1 BrAg, 1 dBrAg, 1 Br, 1 dBr.

Mating.

Parents.

BAg.

dBAg.

BrAg.

dBrAg. \ B.

1

Br.

dB.

dBr.

527

5381 x 5203 . . .

6

3

1

•

1

1

Brown agouti x pink-eyed dilute brown.
Cross 54a. Both parents homozygous, YiBriDiPiAi x YzBr-'diPi. Expectation, all BrAg.

Mating.

Parents.

! BrAg.

1
1

595
G03

Unniarked X unmarked. .
7505 X 7501

1

. 19
7

2G

VI. Dilute Brown Agouti, YBrdPA (Fig. 6).

Eyes brown; ears, feet, and tail hghtlj' pigmented with brown. Ventral hairs dull fawn
Dorsal hairs showing the agouti pattern. The whole appearance is that of a dull, faded,
intense browTi agouti.

EXTENDED SERIES.

65

Dilute brown agouti x pink-eyed dilute brown agouti.

Cro53 55. Dilute brown agouti heterozygous in dark eye crossed with homozygous pinlv-
eyed diUite brown agouti, or pink-eyed dilute brown. YiBriDiPpA-, x FoBr-jd-jpaCAa).
Expectation, 1 dBrAg, 1 pdBrAg.

iNiating.

r,U)
G42</

Parents.

dBrAg.

pdBrAg.

3439xp4519....
76.")0xSn23

12
1

10

13

12

1
I

Dilute brown agouti x brown.

Cross 56. Dilute brown agouti heterozygous in dark eye and agouti crossed with brown
heterozygous in darlc eye. Y>Br'4iPpA x Y->Br>DzPp. Expectation, 3 BrAg, 3 Br,
1 pBrAg, 1 pBr.

Mating. Faivnts.

i

BrAg.

Br.

1

1

pBrAg. j pBr.

428 3439x3739. ...

12 7

1

2

VII. Pink-Eyed Brown Agouti, YBrDpA (Fig. 7).

Eyes clear pink; ears apparently unpigmented, as are also feet and tail. Hairs on ventral
surface indistinguishable superficially from a deep pink-e3^ed yellow. When examined
more closely they are found to be darker at the base than at the tip, showing the pres-
ence of the agouti piittern. Dorsal hair a very rich brownish yellow and deeper colored
at the base with dull brownish pigment. Because of the reduction of brown pigment
at the tips of the hairs the appearance of banding or "ticking " is almost entirely wanting.
Whiskers, hairs at base of ears, and around the anus are yellow.

Pink-eyed brown agouti x pink-eyed brown agouti.
Cross 57. Both parents heterozygous in agouti. Y-iBriDipiA x Y-i-Br-iDyp^A. Expectation,
3 pBrAg, 1 pBr.

Mating.

Parents.

pBrAg.

pBr.

419
399

p unmarked x p2903 ....
»3109 X 7)2903 . .

6
4

1
1

10

2

Cross 58. Both parents heterozygous in density and agouti. Y-iBriDdpiA xY2Br>DdpiA.
Expectation, 9 pBrAg, 3 p5r, 3 pdBrAg, 1 pdBr.

Mating.

Parents.

pBrAg.

pBr.

pdBrAg.

pdBr.

400

p2904 X 7)2903 . .

2

2

1

66

THE INHERITANCE OF COLOR IN MICE.

Pink-eyed broum agouti x broivn.
Cross 59. Both parents homozygous. YiBnBopiAiXYiBriDiPi. Expectation, Br^g only.

Mating.

360

Parents.

BrAg.

p unmarked x 2393 . . . . i 1

Cross 60. Homozygous pink-eyed brown agouti crossed with brown heterozygous in dark
eye. Y2Br2D2p2Ai x YiBviDiPp. Expectation, 1 BrAg, 1 pBrAg.

Mating. Parents.

BrAg.

pBrAg.

261

751395 X 1526

9

4

VIII. Pink-eyed Dilute Brown Agouti, YBrdpA (Fig. 8).

Eyes pink; ears, tail, and feet very lightly pigmented with brown. In both ventral and
dorsal hairs this form resembles a dull intense pink-eyed brown agouti, differing chiefly
in the comparative lack of bright yellow pigment and in the mealy, washed-out look.
The agouti pattern is very weak indeed.

Pink-eyed dilute brown agouti X pink-eyed dilute broum agouti.
Cross 61. Both parents heterozygous in agouti. YiBridiP^A xYiBrid^piA. Expectation,
3 pdBrAg, 1 pdBr.

Mating.

Parents.

pdBrAg.

1

pdBr. 1 p?

479
535

Unmarked x p4519 . .
p4213xp4519

1
1

2

3

2

2 3

Pink-eyed dilute brown agouti x dilute brown.
Cross 61a. Pink-eyed dilute brown agouti heterozygous in agouti crossed with dilute brown
heterozygous in dark eye. YiBrid2P2A x YiBridiPp. Expectation, 1 dBrAg, 1 dBr,
1 pdBrAg, 1 pdBr.

Mating.

Parents.

dBrAg.

dBr.

pdBrAg.

pdBr.

596
005

Unmarked x unmarked . .
7471 x746S

1
2

3

1
2

2

1

3

3

3

3

Cross 61b. Both parents homozygous. Y2Br2d2PiA2XY2Br2d2P2. Expectation, all d5ri4^.

Mating.

Parents.

dBrAg.

609

Unmarked x unmarked. .

2

EXTENDED SERIES.

67

IX. Black, YBiBDP (Fig. 9).

Hairs on ventral surface not so heavily pigmented as the dorsal hairs, and of a dull slaty
black. Tail dark. Dorsal hairs deep, glossy black. Tuft of yellowish hairs at base of
ears. A few yellowish hairs scattered along the flanks, sides and feet. The hairs
around the anus are light yellowish. The feet are dark.

Black X black.

Cross 62. One or both of the parents homozygous. YiBi-iBiD-iPi x YiBr-iB-iDiP'i. Expec-
tation, all B.

Mating.

Parents.

B.

2
2

3
6

401x400...
200 X 201 . . .

4

Cross 63. Both parents heterozygous in black. YoBviBDiPy x YiBriBDiPo. Expecta-
tion, W, 1 Br.

Mating.

Parents.

B. Br.

1x400.. 6 2

Cross 64. Both parents heterozygous in density. YiBr^BiDdPi x YiBr-iB-iDdP^. Expec-
tation, 3 B, 1 dB.

Mating.

Parents.

B. dB.

Ull

7214x7217...

3

3

Cross 65. Both parents heterozygous in dark eye. YoBr^BiDiPp x YiBriB^DoPp. Expec-
tation, 3 B, 1 pB.

Mating.

492
168
189
114
131
135
379

Parents.

Unmarked X 2948

455x919

4.50x540

Unmarked X 454

543x444

450x444

Unmarked x unmarked . .

B.

pB.

3

: 12

6

1 12

2

7

4

60

20

102

30

68

THE INHERITANCE OF COLOR IN MICE.

Cross 66. Both parents heterozygous in dark eye and black. YiBriBDiPp x Y-BriBD^Pp.
Expectation, 9 5, 3 pB, 3 Br, 1 pBr.

Mating.

361

376a

3766

247

318

316

267

364

303

295

349

334

358

333

444

336

447

Parents.

2596x2593

Unmarked x immarked.
Unmarked x unmarked.

1706 X 541

2031 X1942

1948x1950

1948x1949-1950

2084x2086

2084-2085x2086

2186-87-88-89x2184...

2212x2213

2218 X 2213

2210x2219

2210-14x2219

2216x2219

Unmarked X 2593

2945 X unmarked

B.

2

78

13

2

8

5

3

2

11

31

7

6

4

15

4

7

1

VB.

199

1
26

7
1
2
4

3
16

4
5

2
2
1
1

Br.

23
5

i
2
1
2
3
6
2
2
1
6

3
1

75

61

TpBr.

5

2
1

1
4

1
3

V?

19

Cross 66a. Both parents heterozygous in black, dark eye, and density. YiBr2BDdPj).
Expectation, 27 B, 9 dB, 9 p5, 9 Br, 3 pBr, 3 dBr, 3 pdB, 1 -pdBr.

INIating.

Parents.

B.

dB.

pB.

Br.

pdB.

pBr.

dBr.

pdBr.

619
645
646

7515x7513-14-16..

7431 X 7514

7733 X 7734

4
3
3

2

6

2

2

1

1

,

10

2

6

4

2

Cross 66b. Both parents heterozygous in color factor, black, dark eye, and density.
YBr^BDdPp. Expectation, 81 B, 27 dB, 27 pB, 27 Br, 9 pBr, 9 dBr, 9 pdB, 3 pdBr,
64 W.

Mating. Parents.

B.

Br.

W.

625 7430x7428....

i

5

5

3

Black X dilute black.
Cross 67. Both parents homozygous, Y2BriBtD2Pi X YiBriBid^Pi. Expectation, all B.

Mating. Parents.

552

4865x5789..

B.

EXTENDED SERIES.

69

Cross 68. Both parents heterozj-gous in dark eye. YiBriB^DiPp xY2BriB2d2Pp. Expec-
tation, 3 5, 1 -pB.

Mating.

Parents.

B.

pB.

1

197

1363x1435..

4

Black x pink-eyed black.
Cross 69. Both parents homozygous. YiBr-iBiDiPi x Y2Br2BzD2P2- Expectation, all B.

Mating, i Parents.

306

B.

1695xpl510... 16

Cross 70. Black heterozygous in dark eye crossed with homozygous pink-eyed black.
YnBrnB.DiPp X YiBr-iBiDiPi. Expectation, 1 5, 1 pB.

Mating. Parents.

B.

pB.

548
571
220

Unmarked x p5575

3290-96 X p5575

1363xp763

13
6

7

1
1

8

26

10

Black X brown.
Cross 71. Both parents homozygous. YiBr^BiD^Pi X YiBrJDJPi. Expectation, all B.

Mating.

Parents. B.

474

Unmarked X 68 . . 4

Cross 72. Black heterozygous in black crossed with homozygous brown. YiBr^BDiP^. X
YzBriDnPi. Expectation, IB, I Br.

Mating.

Parents.

B.

Br.

308
383
262
390

1631 X1S50

1931x1950

1931 X 1949-50...
2523x2122

20

7

10

14

15
5
5

10

51

35

Cross 73. Black, heterozygous in black, dark eye, and the color factor crossed with pink-
eyed black heterozygous in the color factor and black. YBrzBDiPp x YBriBD^pi.
Expectation, 9 B, 9 pB, 3 Br, 3 pBr, 8 W.

Mating.

Parents.

B.

pB.

Br.

pBr.\

W.

420

Unmarked X 3307...

3

2

5

4

9

70

THE INHERITANCE OF COLOR IN MICE.

Black X pink-eyed brown.

Cross 74. Black heterozygous in dark eye crossed with homozygous pink-eyed brown.
YiBriBiD^Pp X YiBrzDip^. Expectation, 1B,1 pB.

Mating.

Parents.

B.

pB.

475

p unmarked x 68. . .

1

4

Cross 75. Black heterozygous in dark eye and black crossed with homozygous pink-eyed
brown. Y^BriBDiPp x YiBnDiPi. Expectation, 1 B, 1 pB, 1 Br, 1 pBr.

Mating.

Parents.

B.

pB.

Br.

pBr.

493

140x77...

2

1

2

Black X pink-eyed dilute brown.
Cross 75a. Both parents homozygous. YiBr^BiD^Pz x YiBrod^p^. Expectation, all B.

Mating. Parents.

B.

18
4

22

582

7340 X 7341

589

Unmarked x unmarked.. .

Cross 75b. Black heterozygous in dark eye, crossed with homozygous pink-eyed dilute
brown. YiBriBtDiPp x YiBr2diP2. Expectation, 1 5, 1 pB.

Mating.

Parents.

B.

5

pB.
11

620

7472x7475...

X. Dilute Black, YBrBdP (Fig. 10).

Eyes black; ears, tail, and feet moderately pigmented. Ventral hairs slate-colored. Dorsal
hairs are deep blue slate, somewhat washed-out, and at times resembling a very deep-
colored dilute black agouti. There is a small tuft of light hairs at the ba.se of the ears.
Light yellowish hairs scattered on sides and feet, and around the anus. Unlike the
pink-eyed black form next to be described, one would not hesitate in calling the dilute
black animal, black pigmented.

Dilute black x dilute black.
Cross 76. Both parents homozygous. Y2Br2B2d>P2 x Y2Br>B2d2P2. Expectation, all dB.

Mating.

Parents.

dB.

549
457
442

Unmarked x4980. .

4502-03x4497

4502x4497

15

10 !

5 1

1

30

EXTENDED SERIES.

71

Cross 77. Both parents heterozygous in the color factor, black and dark eye.

YBnBdiPp xYBriBdiPp. Expectation, 27 dB, 9 dBr, 9 pdB, 3 pdBr, IG W.

Mating.

Parents.

dB.

dBr.

pdB.

pdBr.

W.

542
511
550

5698x5699

Unmarked x unmarked.. .
Unmarked x 5699

2
3
6

1
1

2

1
4

1
1

2

11

4

5

2

2

Dilute black x pink-eyed black.

Cross 78. Dilute black heterozygous in dark eye crossed with homozygous pink-eyed black.
YoBr^BidiPp X YiBriBiD-iPi. Expectation, IB, 1 pB.

Mating.

Parents.

B.

2

pB.

3
1

337

7^1049x1435

Unmarked x 1435 . .

2

4

Cross 79. Dilute black heterozygous in black crossed with pink-eyed black heterozygous
in density and black. YiBr-iBdiPt x Y^BriBOdp^. Expectation, 3 .6, 3 dB, 1 Br, IdBr.

Mating.

Parents.

B.

Br.

dB.

dBr.

528

p4520x4523....

1

2

2

Dilute black x brown.

Cross 80. Dilute black heterozygous in black, crossed with homozygous brown.
YiBnBdiPi X YiBr^DiPi. Expectation, 1 B, 1 Br.

Mating.

Parents.

B.

Br.

441

2563-64-89x4495..

18

17

Cross 81. Dilute black heterozygous in black crossed with brown heterozygous in density.
YiBr^BdiPi X YiBriDdPo. Expectation, 1 B, 1 Br, 1 dB, 1 dBr.

Mating.

Parents.

B.

Br.

dB.

dBr.

451
437

4501x4857

4501x1404

1
3

2

1

2

4

2

1

2

72

THE INHERITANCE OF COLOR IN MICE.

Dilute black x pink-eyed brown.

Cross 82. Dilute black heterozygous in black crossed with homozygous pink-eyed brown.
YiBr^BdiPi X YiBriDiPi. Expectation, IB, I Br.

Mating.

Parents.

B.

Br.

557

Unmarked x 7^5806

3

2

Cross S2a. Homozygous dilute black crossed with pink-eyed brown, heterozygous in
density. YiBr-iBidiPi x Y^Br-iDdpi. Expectation, \B, IdB.

Mating.

Parents.

B.

dB.

593
612

Unmarked x -7

-8 X unmarked

7
1

5
3

8

8

Cross 83. Dilute black heterozygous in dark eye crossed with pink-eyed brown heterozj'-
gous in density. YiBr2B2d2Pp X YiBriDdpi. Expectation, 1 B, \ pB, 1 dB, 1 pdB.

Mating.

Parents.

B.

pB.

dB.

pdB.

503

4078xp4298...

2

4

XI. Pink-eyed Black, YBrBDp (Fig. 11).
Eyes deep pink; ears very lightly pigmented. Hairs on ventral surface light yellowish-gray.
Tail lightly pigmented. Dorsal hairs varying from a very light yellowish slate color to
a deep lilac. The tufts of light hairs back of the ears are present. No appearance of
black pigment in the dorsal hairs, to the unaided eye. The nose wliiskers are light,
almost yellow. The whole appearance resembles somewhat the dark-eyed dilute brown ,
The feet are slightly pigmented and the hairs around the anus are light.

Pink-eyed black x pink-eyed black.

Cross 84. Both parents heterozygous in black. YiBr^BDip-i x YiBr^BDiPi- E.xpectation,
3 pB, 1 pBr.

Mating.

Parents.

pB.

pBr.

172
342
313

?>845 X p763

pl812xl764

1421-1812x1764..

2

6

10

2

1

6

18

9

Pink-eyed black x brown.

Cross 85. Both parents heterozygous in the color factor. YBviB^Dipi x YBr2D2P2. Expec-
tation, 3B,1 W.

Mating.

Parents.

B.

W.

356

2178x2175..

4

1

EXTENDED SERIES. 73

Cross 86. Both parents homozygous. YiBr2B2Di'Pi x YiBr-iDiP-i. Expectation, all B.

Mating.

Parents.

B.

224
211
230
215
234
270
296
282
281
196
243
236
246
205
381

1717x1512

1049x1630

1042x1630

985x1630

1638-40x1610....

1721 X1609

1765x1603

1608x1603

845x1603

Unmarked X 1603.

1641x1194

1520x1194

Unmarked X 1194.

1524x1192

1524x2175

13

o

4

14

12

9

3

3

6

7

4

9

14

12

3

115

Cross 87. Pink-eyed black heterozygous in black crossed with homozygous brown.
YiBriBD^Pi X YiBviDiPi. Expectation, IB, I Br.

Mating.

Parents.

B.

Br.

274
258
245
266
280

Unmarked x 1764

1642x1764

572x1394

-16x1394

1421 X unmarked ....

3
2
2

I

3
5

1
3
3

11 15

Cross 88. Pink-eyed black heterozygous in the color factor and black crossed with brown
heterozygous in color factor. YBriBD^pi x YBriDiPi. Expectation, 35, 3 Br, 2 W.

Mating.

Parents.

B.

Br.

W.

269

1812x1661

1

4

Cross 89. Pink-eyed black heterozygous in black crossed with brown heterozygous in dark
eye. YzBriBDifi x YiBriD^Pp. Expectation, 1 B,l pB, 1 Br, 1 pBr.

Mating.

Parents.

B.

pB.

Br.

pBr.

257

1714x1526....

2

4

2

4

Pink-eyed black x dilute brown.
Cross 89a. Both parents homozygous. YiBriB^Dip^ x Y^Br^diPi. Expectation, all B.

Mating.

Parents.

B.

648

Unmarked x318. . .

19

74

THE INHERITANCE OF COLOR IN MICE.

Pink-eyed black x pink-eyed brown.
Cross 90. Both parents homozygous. YiBr^BiDiPi x Y2Br2D>p2. Expectation, all pB.

Mating.

Parents.

pB.

634

7804x7800...

4

Cross 90a. Pink-eyed black heterozygous in black, crossed with homozygous pink-eyed
brown. YiBr^BDiPi x YiBriDiPi. Expectation, 1 pB, 1 pBr.

Mating.

Parents.

pB.

pBr.

558
638
640

5721 X5806...
7807x7803...
7809x7803...

1
4
4

2
5
5

9

12

XII. Pink-eyed Dilute Black, YBrBdp (Fig. 12).

Eyes pink; ears, tail and feet extremely lightly pigmented. Coat clearly washed out in
appearance, and a real bluish lilac, at times almost silvery. This variety is very
characteristic, and is one which, when obtained, is easy to recognize. No one would,
without breeding tests, class this form as possessing black pigment.

Pink-eyed dilute black x brown.

Cross 91. Homozygous pink-eyed dilute black crossed with brown, heterozygous in density.
YiBriB'^iPi. X YiBr-iDdP-i. Expectation, 1 B,\ dB.

Mating.

Parents.

B.

dB.

449
594

3627x1404..
19x17...

11

1

9
4

12

13

Pink-eyed dilute black x dilute brown.

Cross 91a. Pink-eyed dilute black heterozygous in black crossed with dilute brown hetero-
zygous in dark eye. Y^Br-iBdipi x Y^Br^diPp. Expectation, 1 dB, 1 dBr, 1 pdB,
1 pdBr.

Mating.

Parents.

dB.

dBr.

pdB.

pdBr.

604

7462 X 7461

2

3

2

EXTENDED SERIES.

75

XIII. Brown, YBrDP (Fig. 13).

Eyes deep brown; ears and tail brown pigmented. Hairs on the ventral surface are lighter
than those on the dorsal surface, and are dull dirty brown. Dorsal hairs deep, glossy
brown; lighter yellowish hairs occur, as in the black variety, at the base of the ears,
scattered on the flanks, sides, and feet, as well as around the anus. The skin is brown
pigmented.

Brown x brown.

Cross 92. One or both parents homozygous. YiBriDiP^xYiBr-zDJP-i. Expectation, only fir.

Mating.

Parents.

Br.

348
345
525

Unmarked x 2291 . .
Unmarked x 2386 . .
5942x5340

5

16

5

26

Cross 93. Both parents heterozygous for the color factor. YBriD2P2 x YBr-iDzPi. Expec-
tation, 3 Br, 1 W.

Mating. ' Parents.

Br.

W.

551 i Unmarked x32...

388 '• 2365x2374

504 4859x4298

575 6225-27x6226....

!

1

4

4

11

11

2
2

2
3

30

9

Cross 94. Both parents heterozygous in dark eye. YiBr^DiPp x Y2Br2D2Pp. Expecta-
tion, 3 Br, 1 pBr.

Mating.

Parents.

Br.

pBr.

406
408

Unmarked x unmarked.. .
Unmarked x unmarked.. .

9
22

3

1

31

10

Cross 95. Both parents heterozygous in dark eye and the color factor. YBviDiPp x
YBriDiPp. Expectation, 9 Br, 3 pBr, 4 W.

Mating.

Parents.

Br.

pBr.

W.

408
366

Unmarked x unmarked .
Unmarked X 2392

22
15

7
4

2
3

37

11

5

76

THE INHERITANCE OF COLOR IN MICE.

Cross 96. Both parents heterozygous in density and dark eye. Y^BriDdPp x YiBriDdPp.
Expectation, 9 Br, 3 dBr, 3 pBr, 1 pdBr.

Mating.

Parents.

Br. i dBr. pBr.

pilBr.

1

1
1

496
569
521
581
632
635

Unmarked X unmarked. .

Unmarked x 4736

4735 X 4736

40
3
6

16
3
2

2

4
1

Unmarked x unmarked . .

7597x7601-02

7439 X 74.37a-.38

15 8

11 2

6 4

81 35 8

3

Brown x pink-eyed brown.

Cross 97. Brown heterozygous in density, dark eye and the color factor, crossed with pink-
eyed brown heterozygous in density and the color factor. YBriDdPp x YBr-iDdpi.
Expectation, 9 Br, 9 pBr, 3 dBr, 3 pdBr, 8 W.

Mating.

Parents.

Br.
3

dBr.

pBr.

pdBr. W.

538

-35x32...

1
.. ! 1

!

■

1 1 3

Brown x pink-eyed dilute hroxon.
Cross 97a. Both parents homozygous. Y2Br2D2Pj. X Y2Brid2p2. Expectation, all Br.

Mating.

Parents.

Br.

1

583

Unmarked x unmarked

1.3

Cross 97b. Brown heterozygous in density crossed with homozygous pink-eyed dilute
brown. YiBr^DdP^ x Y2Br2d2P2. Expectation, 1 Br, 1 dBr.

Mating.

Parents.

Br.

dBr.

584

Unmarked x unmarked

3

2

XIV. Dilute Brown, YBrdP (Fig. 14).

Eyes brown; ears, tail and feet, as in the dilute brown agouti, are lightly pigmented with
brown. Ventral hairs pale fawn. Dorsal hairs dull, washed-out brown, at times
resembUng a dark, pink-eyed black in general superficial coloration. Ear tufts barely
distinguishable from the rest of the coat. The skin is moderately pigmented with brown .

Dilute brown x pink-eyed brown.

Cross 98. Both parents homozygous. Y^Br^diP, x Y2Br2D2p>. Expectation, all Br.

Mating.

Parents.

Br.

495

504

4446 X -77..
4859x4298..

13
11

24

EXTENDED SERIES.

77

Cross 98a. Dilute brown heterozygous in dark eye, crossed with pink-eyed brown heterozy-
gous in density. Y2BridiP]) x YiBnDdp-i. Expectation, 1 Br, 1 dBr, 1 pBr, 1 pdBr.

Mating.

Parents.

Br.

dBr.

pBr.

pdBr.

G08

7479x7478...

3

1

1

3

XV. Pink-Eyed Brown, YBrDp (Fig. 15).
Eyes clear pink. Ears, tail, and feet unpigmented. Hairs on ventral surface dull yellowish
throughout their length. The yellow hairs at the base of the ears and around the anus
are very similar to the rest of the coat, but are, nevertheless, distinguishable from it.
The dorsal hairs are rich fawn colored, lighter than the coat of the pink-eyed brown
agouti.

Pink-eyed broum x pink-eyed broken.

Cross 99. One or both of the parents homozygous. YoBr-iDiPi x Y^BriDip-i. Expectation,
only pBr.

Mating.

Parents.

pBr.

391
390
377
426
524

Unmarked X 3002..
Unmarked x 2821 . .

2799x3002

3310x3309

5805x5945

24

10

3

7
11

55

1

Pink-eyed brown x albino.
(Test matings to determine the gametic constitution of the albinos.)
Cross 100. Pink-eyed brown heterozygous in the color factor crossed with an albino, poten-
tially a homoz3^gous brown agouti. YBr^Dipi X Br-iDiPzAi. Expectation, 1 .BrA^, 1 TT

Mating.

Parents.

BrAg.

IV.

487

5245x4984..

4

6

Cross 101. Pink-eyed brown heterozygous in the color factor, crossed with an albino, poten-
tially a homozygous brown. YBvnDipo x BrzD^Pz. Expectation, 1 Br, 1 W.

Mating.

Parents.

Br.

W.

?
4

500

4082x4286....

13

2

XVI. Pink-eyed Dilute Brown, YBrdp (Fig. 16).

Eyes clear pinlc. Very pale pigmentation throughout hairs and skin, a close approximation
to a dirty brownish cream but still preserving the streaky washed-out appearance
clearly. This form is as characteristic and easily distinguished as the pink-eyed dilute
black. The ear tufts are indistinguishable from the rest of tlie coat. Pink-eyed dilute
browns crossed inter se have given 120 recorded young, all pink-eyed dilute brown.

It must be remembered that all these descriptions of color varieties are intended to bo merely
as they appear to the unaided eye. Many of the regions here spoken of as pink or
unpigmented have, upon microscopic examination, yielded a small amount of pigment.

78 THE INHERITANCE OF COLOR IN MICE.

RESTRICTED SERIES.

All animals in this series, that is to say, all yellow animals, are of the zygotic formula Rr.
The combination RR, if formed, fails to develop.

(a) Dark-eyed intense series.

This series consists of four types of yellows :

XVII. Black-eyed Yellow Carrying Agouti, YBrBDPAR (Fig. 20).
XVIII. Black-eyed Yellow Without Agouti, YBrBDPR (Fig. 17).
XIX. Brown-eyed Yellow Carrying Agouti, YBrDPAR.
XX. Brown-eyed Yellow Without Agouti, YBrDPR (Fig. 18).

Types XVII and XVII are similar in appearance, and are indistinguishable save by breed-
ing tests. Types XIX and XX also are only to be distinguished from each other by
suitable test matings.

(b) Pink-eyed intense series.

This series consists of four types of yellow which are indistinguishable in external appearance:

XXI. Pink-eyed Yellow Carrying Black Agouti, YBrBDpAR.
XXII. Pink-eyed Yellow Carrying Black, YBrBDpR.

XXIII. Pink-eyed Yellow Carrying Brown Agouti, YBrDpAR.

XXIV. Pink-eyed Yellow Carrying Brown, YBrDpR.

Test matings are necessary before these forms can be distinguished from each other.

(c) Dark-eyed dilute series.
In this series also there are four tj^pes:

XXV. Black-eyed Dilute Yellow Carrying Agouti, YBrBdPAR.
XXVI. Black-eyed Dilute Yellow Without Agouti, YBrBdPR.

XXVII. Brown-eyed Dilute Yellow Carrying Agouti, YBrdPAR.
XXVIII. Brown-eyed Dilute Yellow Without Agouti, YBrdPR (Fig. 19).

In this series types XXV and XXVI are distinguishable from types XXVII and XXVIII

by a careful examination of the eyes. Such a test, however, is not certain enough to

be considered final, and a breeding test forms the only sure basis for a permanent

classification.

(rf) Pink-eyed dilute series.

As in the pink-eyed intense series the four forms of this series are indistinguishable save by
breeding tests. This is because of the fact that the total amount of pigment in the
eye is so small that it is impossible to determine whether it is brown or black by any-
thing short of a microscopic examination. The gametic formulae follow:

XXIX. Pink-eyed Dilute Yellow Carrying Black Agouti, YBrBdpAR.
XXX. Pink-eyed Dilute Yellow Carrying Black, YBrBdpR.
XXXI. Pink-eyed Dilute Yellow Carrying Brown Agouti, YBrdpAR.
XXXII. Pink-eyed Dilute Yellow Carrying Brown, YBrdpR.

Each of these series may now be considered separately.

Up to a certain point there were no pink-eyed or dilute mice, yellow or non-yellow in my
stock. All the yellows were therefore intense dark-eyed yellows and would group them-
selves under one of the first four types (XVII, XVIII, XIX, or XX). To test them a
cross with any type of brown animal lacking the agouti factor would suffice.

A list of such crosses follows. Yellows which proved to be of type XVII are included in the
following table:

RESTRICTED SERIES.

79

Mating.

Parents.

F.

BAg.

Zygotic formula
of yellow parent.

29
34
36

700-702 br. x 508 yel..
707 br. x502.4Ayel...
502.2A yel. xbr

2
6

1

5
2
3

YiBviBiDiPiAoR.

9

10

All these yellows seem to have been homozygous in the factors for black and for agouti.
Yellows of type XIX follow :

Mating.

Parents.

F.

BrAg.

Br.

Zygotic formula
of yellow parent.

15-111-85

18-19

56

82

146 yel. x brown. .

br. X 571 yel

br. X 148 yel

502.1Byel. xbr...

12

1
2
2

8
5
1
3

1

2

Y2Br2D2P2AR.
Y2Br2D2P2A2R.
Y2Br2D2P2A2R.
Y2Br2D2P2AR.

17

17

3

There are two types of zygotes here, those homozygous in the agouti pattern (A) and those
heterozygous, the latter giving non-agouti, as well as agouti young.

The yellows of type XVIII are also of two sorts, those homozygous in the factor for the
production of black (B) and those heterozygous in this factor. Thus in the following
table 502.21A yellow is known to be an animal homozygous in the factor B, while all
the other yellow animals are heterozygous, producing browns as well as blacks.

Mating.

Parents.

F.

B.

Br.

Zygotic formula
of yellow parent.

63
11
37

92
100
320

502.21 A yel. xbr....

br. X 505 yel

502.22Ayel. xbr....

br. X 228 yel

326 yel. xbr

2320 yel. xbr

2

1

1
1
1
4

1
1
2
2

1

2

1
2
1
1

1
1

Y2BriB2D2P2R.

Y2Br2BD2P2R.

Y2Br2BD2P2R.

Y2Br2BD2P2R.

Y2Br,BD2P2R.

Y2Br2BD2P2R.

10

9

6

Type XX, yellows which give browns only, are seen in the following table:

Yelloxv X brown.

Mating.

Parents.

F.

Br.

Zygotic formula
of yellow parent.

62

232

293

329

331
304-314
327-222
141-142
151-170

597

601

602

502. 23 A yel. xbr....

br.x 1316 yel

br. X 988 yel

2319 yel. xbr

2109-2110 yel. xbr..

2109 yel. xbr

br. X 1001 yel

br. X 580 yel

br. X 881-883 yel ... .
yel. X br

2
1
3
3
1

13
5

11
4
6
6
1

1

7
2
4

3
4
5
9

4

I

Y2Br2D2P2R.
Y2Br2D2P2R.
Y2Br2D2P2R.
Y2Br2D2P2R.
Y2Br2D2P,R.
Y2Br2D2P2R.
YrBr.D^P^R.
Y2BroD2P2R.
Y2Br2D2P2R.
Y2Br2D2P2R.
Y2Br2D2P2R.
Y2Br2D2P2R.

yel. X br

br. X 7488 yel

56

48

80

THE INHERITANCE OF COLOR IN MICE.

It has been shown, then, that yellows of the four dark-eyed intense pigmented types exist.

The pink-eyed yellows (types XXI-XXIV inclusive) have been crossed only inter se or with
black pigmented forms, but it is certain that they also can occur in the four types com-
parable to the dark-eyed intense series.

The dark-eyed dilute yellows have been crossed with brown only in a few cases. Chiefly
they have been bred inter se to determine whether the 2 : 1 ratio holds good in their
case as in the intense forms. Of those tested, one, 9 7298, is of the zygotic formula
Y2Br2Bd2PpA2R and when crossed with a pink-eyed brown has given 1 yel, 1 pdijel,
1 BAg, 2 BrAg, 1 pBAg. This shows that types XXV and XXVII can exist. The
other animal, also a female, gave by a pink-eyed brown male, 7 yeJ, 2 pyel, 2 Blk, 2 Br,
3 pB. This animal was of the formula YiBr^Bd^PpR, and argues strongly in favor of
the existence of types XXVI and XXVIII.

Of the pink-eyed dilute yellows few have been tested, but I have, at present, a race of animals
which give only two sorts of young, viz, pink-eyed dilute yellows and pink-eyed dilute
browns; such pink-eyed dilute yellows are the ultimate recessives of the yellow series
belonging to type XXXII, formula YiBr-idiPiR.

From the few matings given above, together with the larger number of yellow matings which
follow, it is easy to see that yellows may be obtained of the various zygotic compositions
found in the non-yellow varieties, differing from them only by the addition of the restric-
tion factor, R.

We shall first consider the crosses between yellow animals of these four varieties, which form
the intense dark-eyed series.

Yellow X yellow, giving only dark-eyed intense young.
Cross 102. Giving Y and Br.

Mating.

Parents.

}'.

Br.

127
38
39
255
301
297
571
166

425 X 424

4

4
5
4
2

6
12

3

3

1
2

1
1

7

502.23A X 502.5B

Unmarked x 505.1 A. .

1410x1667

1747 X 49-1746

1723x1827

7180x7181

893x895

37

21

Cross 103. Giving Y, Br, and 11' (and in one case BrAg).

Mating.

Parents.

384
118
145
178
185
183
326
352

Unmarked x unmarked

578x580

146x895

146-894x895

894x895

146-893-94x895

1247x2311

726-1247x2311

Y.

BrAg.

Br.

W.

22

1

6

1

4

1

5

8

7

3

1

1

5

2

3

8

1

1

^

1

1

46

1

26

18

RESTRICTED SERIES.

81

Citoss 104. Giving Y, BAg, B, and W.

Matini^.

Parents.

Y.

3
10
7
2
5
2

BAg.

B.

W.

8

9

10

15

248

570

502.1 Ax 502..^) A...
502.2Ax502.5A....
502x511

2
2

1

3
3

2
1
3

1

509 x511

1247x1316

Unmarked X 3297 . .

29

4

1

13

Cuoss 105. Miscellaneous yellows giving Y, BAg, and B.

Mating.

Parents.

Y.

BAg.

B.

BAg or B.

529

283

264

27

14

7

22

28

Unmarked X 1938.
1723 X unmarked. .

1666 X 1667

509.1Ax511

509 x 510

38

1
3
3
5
1
4

1

V
1

]

[1
1

I

502 X 503

514.6Ax505.1A...
514.4Ax.505.lA...

55

3

12

4

Sooty yelloic x sooty yelloiv, giving only dark-eyed intense young.
Cicos3 106. Giving Y, sY, B, and B.Xg.

Mating.

Parents.

Y.

sY.

BAg.

B.

B or BAg.

440
471

502

3196 x3777

3

1
15

1

8

13

3
4

2
10

1

Unmarked x 3957 . . .
Unm^arked x 3777 . . .

19

22

7

12

1

Cream x cream, giving nothing hut dark-eyed intense young.
Cross 107. Giving cream, or light yellow, B and Br.

Mating.

Parents.

Cream Y.

B.

Br.

284
445
122

285

1248x1414

.3907x875

648x647

1750 X 1745-46. .

4

2

2

1
2

i

2

8

3

4

82 THE INHERITANCE OF COLOR IN MICE.

Cross 108. Giving cream, BAg, B, Br, and W.

Mating.

Parents.

Cream Y.

BAg.

B.

Br.

W.

397
469
325

188
418

3908 X 875

4
1

7

3

2
1

2
2
2

4

1
2

4068x4796

2050x875

1248x580

Unmarked X 875...

15

3

6

7

5

Yellow X cream, giving nothing but dark-eyed intense young.
Cross 109. Giving Y, B, BrAg, and Br.

Mating.

Parents.

Y.

B.

BrAg.

Br.

4.50
233

Unmarked X 3906 . . .
882 X 601

36
1

10

3

5

1

37

10

3

6

Cross 110. Giving Y, B, BrAg, Br ?, and W.

Mating.

Parents.

Y.

B.

BrAg.

B or Br.

W.

273

272

2049x875...
2048x875...

5
4

1

v

1

1

4

9

1

1

1

4

Cross 111. Giving Y, cream, B, Br, and W.

Mating.

Parents.

Y.

Cream Y.

B.

2
1
1

Br.

W.

146
123
154

284x875...
284x647...
882 X 881 . . .

1
10

5
5
2

3

8

3

11

12

4

11

3

Yellow X ydloiv, giving intense and dilute dark-eyed young.
Cross 112. Giving Y, BAg, BrAg, Br, dY, dBAg.

Mating.

Parents.

Y.

dY.

BAg.

dBAg.

BrAg.

Br.

164
250

620x621

1658 X 1660. . . .

o
10

3

2

1

1

1

12

3

2

1

1

1

RESTRICTED SERIES.

83

Cross 113. Giving Y, BAg, dBAg, and W.

Mating.

Parents.

Y.

BAg.

dBAg.

W.
5

23

530x511...

5

3

1

Yellow X yellow, giving intense dark-eyed and intense pink-eyed young.
Cross 114. Giving Y, pY, B, pB, Br, and pBr.

Mating.

Parents.

Y.

pY.

B.

Br.

2

pB.

p5r.

321
311
393

2198x2197

1947x1877

Unmarked x unmarked . .

7
4
3

2
2

5
6

1

2

2

1

14

4

12

2

4

1

Cross 114a. Giving Y, sY, pY, BAg, B, BrAg, Br, pBAg, pB, pBr, and pL

Mating.

Parents.

Y. sY.

pY.

BAff.

B.

Z?r^ff. .Br.

pBAg.

pB.

pBr.

pf

477
459
256
244
287

Unmarked X 5228..
Unmarked x4631 . .

1722x1827

1724x1827

1722-24x1827

45

7
7
4
4

3
1
1

1

2
2

2
5

2

ii

11

2

1
2

6

4

.. I 1

1

i

1

\

67

6

13

11

16

4 1 9

1

1

3

1

1

Cross 115. Giving Y, pY, BAg, BrAg, B, Br, pB, and W.

Mating. Parents.

Y.

pY.

BAg.

BrAg.

B.

Br.

pB.

PF.

430 3299 X 3297 ....
159 786x784

5
4

1
1

i

2

4

1

1

3

1

9

2

1

2

4

1

1

4

Sooty yellow x yellow, giving intense dark-eyed and intense pink-eyed young.
Cross 116.

Mating.

Parents.

Y.

SY.

251
240
278
328
362
367
339
353
354
460
415
411
485
472

1826x1829

1828x1829

1826-28x1829

2666-67x1829

2666x1829

Unmarked x 1829

2668x1829

2667x1829

2665x1829

Unmarked x unmarked.

Unmarked X 3460

Unmarked X 3640

Unmarked x 3777

Unmarked x 3957

2
5
3
6
1

38
6
1
5
4

10
3
4

24

1

i
1

10

3

1

4
9

112 32

pY. BAg.

13

1
14

22 15

BrAg.

B.

Br.

1

18

i

3

2

34 I 17

pBAg.

pB.

2
1

1
6

10

pBr.

84

THE INHERITANCE OF COLOR IN MICE.

Yellow X yellow, gicing inlcnse and dilute dark-cycd and pink-eyed young.
Cross 117.

Mating.

Parents.

Y. pY.

BAg.

dBAg.

pBAg.

pdBAg.

pdB.

pdBr.

W.

446

Unmarked x 4054. .

6 2

2

2

1

1

1

1

1

Yellow X yellow, miscellaneous.
Cross 118. No color varieties recorded.

Mating.

Parents.

Y.

non Y.

W.

556
555
579
544
568
543
565
572

Unmarked X 4334

Unmarked x 4523

Unmarked x 4631

Unmarked x 4712

Unmarked X 4891

Unmarked x 4905

Unmarked x 4149

Unmarked x unmarked . .

4
9
11
5
5
2

3

77

2
3

9

2

4

38

2

116

58

2

Yellow X dilute yellow, giving nothing but intense dark-eyed young.
Cross 119. Giving Y, BAg ?, B, BrAg, and Br.

Mating.

Parents.

Y.

BAg or B.

B.

BrAg.

Br.

546
564
520

Unmarked x 5155

Unmarked x 4710

Unmarked X 4334

14

2

1

1

2

3

2
1

17

1

2

3

3

Yellow X dilute yellow, giving intense and dilute dark-eyed young.
Cross 120. Giving Y, dY, dBAg, BrAg, and dBrAg.

Mating.

Parents.

Y.

dY.

dBAg.

BrAg.

dBrAg.

567
566
553

Unmarked x 4146

Unmarked x4712

Unmarked x 4905

2
6
2

Q

i

l"

1

1
1

10

6

1

1

3

Yellow X dilute yellow, giving only intense dark-eyed and pink-eyed young.
Cross 121. Giving Y, pY, BAg, BrAg, B, and W.

Mating.

Parents.

Y.

pY. BAg.

BrAg.

B.

W.

476

Unmarked x4710...

10

1 2

1
j

2

1

1

RESTRICTED SERIES.

85

Yellow X dilute yellow, giving intense and dilute dark-eyed and pink-eyed young.
Cross 122. Giving Y, pY, dY, pdY, BAg, dBrAg, dB, or dBAg.

Mating.

Parents.

Y.

dY.

pY.

pdY.

BAg.

dBrAg.

dB or dBAg.

563
533

Unmarked X 4631 ....
Unmarked X 5008...

1
11

1
5

1

1

1

1

i

12

6

1

1

1

1

2

Yellow X dilute sooty yellow, giving intense and dilute dark-eyed young.
Cross 123. Giving Y, sY, dY, dsY, BAg, BrAg, dBAg, and dBrAg.

Mating.

Parents.

Y. ! sY.

dY.

dsY.

BAg.

BrAg.

BAg or BrAg.

dBAg.

dBrAg.

^63
514

Unmarked X 4346.
Unmarked X 2348.

9 i 2
5 1

1
5

3
4

6
2

4

1

3

1
1

1

14 3

6

7

8

5

3

2

1

Yellow X pink-eyed yellow, giving only intense dark-eyed young.
Cross 124. Giving Y and BAg.

Mating.

Parents.

Y.

BAg.

554
99

Unmarked x 4149. . . .
227x413

3

4

1

7

1

Yellow X pink-eyed yellow, giving intense and dilute dark-eyed young.
Cross 125. Giving Y, B, and dB.

Mating. Parents.

Y.

B.

dB.

125

326x563

4

1

2

Yellow X pink-eyed yellow, giving intense pink-eyed and dark-eyed young.
Cross 126. Giving Y, pY, B or BAg, B, Br, pBrAg, and pB.

Mating.

200
216
514
473

Parents.

1282x1389

1283 X 1389

Unmarked x 4523

Unmarked x unmarked.

F.

1
1

2
2

pY.

1

o

BAg or B.

B.

Br.

pBrAg.

pi?.

p?

2

3

1

1

1

'3

1

2

4

1

1

3

1

86

THE INHERITANCE OF COLOR IN MICE.

Cross 127. Giving Y, vY, BAg, B, Br, pB, and W.

Mating.

Parents.

Y.

1

4

pY.

1
2

BAg.

B.

Br.

pB.

W.

501
532

(a) unmarked x 3297 . . .
(6) unmarked x 3297...

1

1

1

1

2

2

5

o

1

1

1

1

4

Yellow X pink-eyed yellow, giving intense and dilute dark-eyed and pink-eyed young.
Cross 128. Giving Y, pY, dBAg, and pdBAg.

Mating.

Parents.

Y.

pY.

dBAg.

pdBAg.

530

Unmarked x 4152. .

1

2

1

1

Creayn x pink-eyed yellow, giving nothing but dark-eyed intense young.
Cross 129. Giving Y and BAg.

Mating.

Parents.

F. BAg.

I

184
210

1223x1074..
1223x1064..

3

14

1

17

1

In the following crosses, between yellow and non-yellow animals, equality of yellow and
non-yellow young is to be expected. These matings, like the yellow x yellow matinga
just cited are planned chiefly to test the relation of yellow to non-yellow forms, not
with an eye to producing any certain color variety.

Yellow X black agouti, giving only dark-eyed intense young.
Cross 130. Giving Y and BAg.

Mating.

Parents.

Y.

BAg.

12
24

506x530.5A

530.1Ax630

3

1

4

7

4

11

Cross 131. Giving Y, BAg, and W.

Mating.

Parents.

Y.

BAg.

W.

16

608x570....

2

1

1

RESTRICTED SERIES.

87

Cross 132. Giving Y, BAg, BrAg, and W.

Mating.

Parents.

Y.

BAg.

BrAg.

W.

95

622x624...

2

1

1

1

Yellow X black agouti, giving intense and dilute aark-eyed young.
Cross 133. Giving Y, BAg, and dBAg.

Mating.

Parents.

F.

BAg.

dBAg.

26

530.1Ax530.5A

1

5

1

Yellow X black agouti, giving intense and dilute dark-eyed and -pink-eyed young.
Cross 134. Giving Y, dY, pY, BAg, dBAg, BrAg, dBrAg, B, pB, and Br.

Mating.

Parents.

}'.

dY.

pY.

pdY.

BAg.

dBAg.

BrAg.

dBrAg.

B.

pB.

Br.

489
375

Unmarked x3114. . . .
Unmarked X 3114-15.

11
24

1

8

2

4
10

3
5

2
8

1
1

2
1

1

2
1

35

9

2

14

8

10

2

3

1

3

Cream x black agouti, giving intense dark-eyed young only.
Cross 135. Giving cream and BAg.*

Mating.

Parents.

Cream Y.

BAg.

443
434

Unmarked x unmarlced ....
2108-09 x3947

1

2

1
1

3

2

*The black agoutis used in this cross were wild.
Cross 136. Giving Y, BAg, and B.

Mating.

Parent.

F.

BAg.

B.

265

917x1550

3

2

1

Cross 137. Giving F, BAg, and BrAg.

Mating.

Parents.

F.

BAg.

BrAg.

534

4798 X 4796. . .

2

1

1

88

THE INHERITANCE OF COLOR IN MICE.

Yellow X dilute black agouti, giving only intense dark-eyed young.
Cross 138. Giving F, BAg, and BrAg.

Mating.

Parents.

F.

BAg.

BrAg.

322
412

2154x1871

4
2

2

2

Unmarked x unmarked . . .

6

2

2

Yellow X dilute black agouti, giving intense and dilute dark-eyed young.
Cross 139. Giving F, dY, BAg, dBAg, B, dB, BrAg, and Br.

Mating.

Parents.

F.

dY.

BAg.

dBAg.

B.

dB.

BrAg.

Br.

438
432
409
421

4435 X 2829

4

4

10

2

1
1

8

3

1

1

3

3
1

1
1

4434-35 X 2829

Unmarked x 2829

2352 X 2859

20

10

3

1

1

3

4

2

Cream x dilute black agouti, giving intense and dilute dark-eyed young.
Cross 140. Giving F, dF, dsY, and Br.

Mating.

Parents.

F.

dF.

dsF.

Br.

373

2348 X 2829. .

4

2

1

1

Cross 141. Giving F, B^j/, d^rA^, and W.

Mating. Parents. , F. i B^^. i dBrAg. W

402 : 2255x1938. . J 4

1

*Soo<«/ yellow x di7wte fciacA; agouti, giving intense dark-eyed and pink-eyed young.
Cross 142. Giving F, sF, pF, BAg, and /^iJ^r/.

Mating.

Parents.

F.

sY.

pF.

B^?.

B or 5.4ff.

pBAg.

346

2411x2609

11

7

3

17

6

2

Yellow X pink-eyed black agouti, giving only intense dark-eyed young.
Cross 143. Giving F, BAg, and j^.

Mating.

76

78

Parents.

F.

BAg.

B.

509.2Bx409. ..
227x412

9

9

8

6
5

9

17

11

RESTRICTED SERIES.

89

Yellow X pink-eyed black agouti, giving intense and dilute dark-eyed young.
Cross 144. Giving Y, BAg, dBAg, and BrAg.

Mating.

330

Parents.

1667x1876.

Y. BAg. dBAg.

BrAg.

Yellow x pink-eyed black agouti, giving interne and dilute dark-eyed and pink-eyed young.
Cross 145. Giving Y, BAg, dBAg, pBAg, B, and pB.

Mating.

Parents.

Y.

BAg.

pBAg.

dBAg.

B.

pB.

371

1806x2339

8

1

1

1

2

1

Cross 146. Giving Y, pY, dY, pdY, B, dB, and W.

Mating.

Parents.

Y.

pY.

dY.

pdY.

B.

dB.

W.

433

4051 X unmarked . . .

5

4

1

1

2

2

4

Yellow X black, giving only dark-eyed intense young.
Cross 147. Giving Y and BAg.

Mating.

Parents.

Y.

BAg.

54
49
90
61

502 xl77

5
4
2

3

2
3
5
2

185 x315

Unmarked x 502. 5B. .
502.3B X unmarked . .

14

12

Cross 148. Giving only Y and B.

Mating.

Parents.

Y.

B.

370
52
53
88

137
40

1977x2046

502.22BX182

509 X 182

Unmarked x 321

224x347

Unmarked x 505.1 A. .

3
2
2

4

2

3
4
2
1
2

11

14

90

THE INHERITANCE OF COLOR IN MICE.

Cross 149. Giving Y, BAg, and B.

Mating.

Parents.

Y.

BAg.

B.

35
103

207x502.6B

225x347

3

2

2

1

2
5

5

3

7

Cross 150. Giving Y, B, and Br.

Mating.

Parents.

Y.

B.

Br.

117
292

238

328x323

2

5
3
3

1
1
1

1662x1660

1662-63x1660

7
7

16

11

3

Cross 151. Giving F, BAg, and W.

Mating.

Parents.

Y.

BAg.

W.

46
47
17
42
43

178x530.018

509.3Bxl77

206x510

3
3
2
2
1

1
1
3

1
1

1
3
2
3
3

201.1Ax511

201.2Ax511

11

7

12

Cross 152. Giving Y, B, and W.

Mating.

Parents.

Y.

B.

W.

59
21

72
58
51

Unmarked x 141.. .

206x514

178x320

4
3
6
3

1

1

2
8
1
2

1
3

3
2
o

168-170-171x185..
206 X 172

17

14

11

Cross 153. Giving Y, cream, BAg, BrAg, B, and Br.

Mating.

Parents.

Y.

Cream Y.

BAg.

BrAg.

B.

Br.

73

71

108

357

91

-67 X unmarked. . .
284 X 182

5

15
7
3
5

1

5
1
3

1

V
1

2

4
Y

4
3

Unmarked x 323 . .

1978x2406

328 X 502.5B

35

1

9

5

5

7

RESTRICTED SERIES.

91

Cross 154. Giving Y, cream, BAg?, B, Br, and W.

Mating.

Parents.

Y.

Cream Y.

BAg or B.

B.

Br.

W.

57
80
94

152xl.lA....

185x319

185x348

4
4
9

3

i

3
5
9

1
1
2

1

1

10

17

3

1

17

4

12

Cross 155. Giving Y, BAg, BrAg, B, and W.

Mating.

Parents.

Y.

BAg.

BAg or B.

B.

BrAg.

W.

41
55
70
133
66

206x510.2A

6
6
2
6

5

1
2

5

5
1

4
1

2

1
2
3

2
2
5
5
2

184 X 148a

Unmarked x 319

325 X unmarked

502. 2B X unmarked. . .

20

8

11

5

8

16

Yelloio X black, giving intense and dilute dark-eyed young.
Cross 156. Giving Y, B, Br, and dB.

Mating.
276

Parents.

Y.

B. Br. dB.

1663x1660

2

5

2 1

Yellow X black, giving intense dark-eyed and pink-ej/ed young.
Cross 157. Giving Y, pY, B, and pB.

Mating.

Parents.

Y.

pY.

B.

pB.

341
491
456

2195x2197

2

3

6
2

1
1
1

Unmarked x 2948 . . .
2803 X 2948

5 1
3 1

10

2

11

3

Cross 158. Giving Y, cream, pY, B, Br, pB, and pBr.

Mating.

Parents.

Y.

Cream Y.

pY.

B.

Br.

pB.

pBr.

p?

424
319
290
121
214

2803 X unmarked

1941 X 1942

3

6

2

14

14

Y

3
1

3

9
9
4
6
13

1
5
1

5

2

1
2
2
3
6

i

3

1

2

1882x1877

549x540-41-42-44...
549 X 541

39

1

7

41

14

14

5

2

92

THE INHERITANCE OF COLOR IN MICE.

Cream x black, giuing only intense dark-eyed young.
Cross 159. Giving Y, B, and Br.

Mating.

Parents.

Y.

3
3

B.

Br.

217

2SS

Unmarked x988....
2092 X 989

1
2

1
2

6

3

3

Cross 160. Giving Y, B, Br, and W.

Mating.

Parents.

Y. B.

Br.

W.

156

328x988. . .

11 3

10

7

Cream x dilute black, giving only intense dark-eyed young.
Cross 161. Giving Y and ?

Mating. Parents.

312

1751 X1435.

Y.

Yellow X dilute black, giving i/ilense and dilute dark-eyed young.
Cross 162. Giving Y, dY, dB, and dBr.

Mating.

Parents.

Y.

dY.

dB.

dBr.
1

448

4499x4196. . .

1

2

3

Yellow X pink-eyed black, giving only dark-eyed intense young.
Cross 163. Giving Y and B.

Mating.

Parents.

Y.

B.

1
7
5

271

289
307

1639x1587...
1666x1610...
2049x1610...

2
5
1

8

13

Yellow x pink-eyed, black, giving intense dark-eyed and pink-eyed young.
Cross 164. Giving Y, Br, and pB.

i

Mating. Parents.

Y.

Br.

pB.

309

2050x2062

4

1

1

RESTRICTED SERIES.

93

Cream x pink-ci/cd bliick, yii'ing onlij (hirk-vycd iiUcuse young.
Cross 165. Giving Y, cream, and B.

Mating.

Parents.

1'.

Cream Y.

B.

299
180
204
225

1105x1414

12.56x1192

1195x989 . .. .

2
i 10

; 1

i 7
8

3
2

3

15

I

10

1193x989

Unniarkod x unmarked . .

28

5

37

Cross 166. Giving Y, sY, B, and Br.

Mating.

Parents.

Y.

sY.

B.

Br.
2

208

1411x1394...

4

1

4

Cross 166a. Giving Y, cream, Br, and W.

Mating.

Parents.

Y.

Cream Y.

Br.

W.

226

1105x580. ...

2

1

2

2

Yellow X b7-own agouti, giving only intense dark-eyed yoking.
Cross 167. Giving Y and BAg.

Mating.

Parents. BAg

30 511.2Bx502.4A.. 4

Cross 168. Giving Y and BrAg.

Mating.

Parents.

Y.

BrAg.

1

5
4

32
110
461

575x502. 5 A

427 X 424

3

2

4.340 X unmarked.. .

5

10

Cross 169. Giving Y, BAg, and B.

Mating.

Parents.

Y.

BAg.

B.

50

511.1Axl40. . .

5

1

2

94 THE INHERITANCE OF COLOR IN MICE.

Cross 170. Giving Y, BrAg, and Br.

Mating.

Parents.

Y.

BrAg.

Br.

191

892x895

2

3

1

Cross 171. Giving Y, BrAg, and W.

Mating.

Parents.

Y.

BrAg.

W.

75

170x410

1

5

2

Cross 172. Giving Y, BrAg, Br, and W.

Mating.

Parents.

Y.

BrAg.

Br.

W.

176

891x895

9

2

5

6

Ydlow X brown agouti, giving intense and dilute dark-eyed young.
Cross 173. Giving Y, BAg, BrAg, and dBrAg.

Mating.

Parents.

Y.

BAg.

BrAg.

dBrAg.

69

171x411....

7

5

5

1

Cross 174. Giving Y, dY, and dBrAg.

Mating.

1
1

Parents. Y.

dY.

dBrAg.

423

3414x3413.... 1

1

2

4

In the following niatings the yellow parents were dilute, and of four different sorts, riz:

Dilute black-eyed yellow, Y 2Br2Bid2P2A2R;
Dilute black-eyed yellow, Y2Br2B2d2P2R;
Dilute brown-eyed yellow, Y2Br2d2P2A2R;
Dilute brown-eyed yellow, Y2Br2d2PiB.

These four varieties are extremely difficult, if not impossible, to tell from one another by
superficial examination. The two brown-eyed types may, however, be distinguished at
times by their eye-color, which is, as in the corresponding intense types, always brown .
The following description will apply then to these four varieties:

Eyes black or brown, ears pink. Ventral hairs much the same as in the intense yellow type.
Tail unpigmented. Dorsal hairs a dull heavy yellow with the characteristic washed-out
appearance of all dilute forms. Hairs at the base of the ears and around the anus are
indistinguishable from the rest of the coat.

RESTRICTED SERIES.

95

Dilute yellow x dilute yellow, giving only dilute dark-eyed young.
Cross 175. Giving dY and dBAg.

Mating.

Parents.

dY.

dBAg.

499

Unmarked x 3875

9

2

Cross 176. Giving dY and dB.

Mating.

Parents.

dY. dB

547 i Unmarked X 5155 ' 6

Cross 177. Giving dY, dBAg, and dBrAg.

Mating.

Parents.

dY.

dBAg.

dBrAg.

382
481

482

3401 X 22.33

Unmarked x 4456. .
Unmarked x 4712. .

9
15
25

2
8
2

3
4

9

49

12

16

Cross 178. Giving dY, dBAg, dBrAg, and dBr.

Mating.

Parents.

,Y.

dBAg.

dBrAg.

dBr.

484

Unmarked x 4334

8

1

3

3

Cross 179. Giving dY, dBrAg, and W.

Mating. Parents.

dY.

dBrAg.

W.
3

483 4147x4146....

4

2

Cross ISO. Giving dY, dBAg, dBrAg, and IF.

Mating.

Parents.

dY.

531

dBAg. dBrAg. I W

Unmarked x 4146 1 9 1

Dilute yellow X pink-eyed yellow, giving intense and dilute dark-eyed young.
Cross 181. Giving dY, BAg, B, dBAg, and dBrAg.

Mating.

500

Parents.

dY.

Unmarked X 4152.. I 2

BAg. j B. dBAg. ; dBrAg.

96

THE INHERITANCE OF COLOR IN MICE.

Dilute yellow x pink-eyed yellon:, giving intense and dilute dark-eyed arid pink-eyed young.
Cross 182. Giving Y, pY, dY, vdY, BAg, dBAg, B, and pB.

Mating.

Parents.

Y.

pY.

dY.

pdY.

BAg.

dBAg.

B.

pB.

BAg or B.

545

480
467
539

Unmarked x4152.
Unmarked x 3875.

4524x4523

Unmarked X 4523.

2
1
2

2
3
3

1

3
1

2

1

2

1

1
2

Y

2

5

8

5

3

2

1

3

1

9

Dilute yelloiv x pink-eyed dilute yellow, giving only dilute dark-eyed young.
Cross 183. Giving dY, dBAg, and dB.

Mating.

Parents.

dY.

dBAg.

dB.

512

Unmarked x3875....

15

8

2

Dilute yellow x it'i'W black agouti, giving intense dark-eyed young.
Cross 184. Giving Y and ?

Mating.

Parent.-?.

1'

523 : 4345x5160-5161 ... 1

Dilute yellow x dilute black agouti, giving dilute dark-eyed young.
Cross 185. Giving dY, dsY, and dBAg.

Mating.

Parents.

dY.

dsY.

dBAg.

439
417

3553x3876

3554x3875

7
5

1

5
3

12 1 1

8

Dilute yellow x dilute brown agouti, giving only dilute dark-eyed young.
Cross 186. Giving dY, dBAg, and clBrAg.

Mating.

Parents.

dY.

dBAg.

dBrAg.

450
427
431
343

4023-24x4021-22....

4024x4021-22

4023x4021-22

2259 x2233

1
8
6
6

5

4
4

5

5
1
3

21

13

14

RESTRICTED SERIES.

97

Dilute sooty yellow x dilute brown agouti, giving dilute dark-eyed and pink-eyed young.
Cross 1S7. Giving dsY, pdY, dBAg, and dBrAg.

Mating.

Parents.

dsY.

pdY.

dBAg.

dBrAg.

490
465

4803 X 4573

3

2

1

1

1

1

Unmarked x 4753 . . .

5

2

1

1

In the following crosses, the yellow parents were pink-eyed, and of four different types, viz.:
Pink-eyed yellow, Y^Br^.B-.D^piAiR;
Pink-eyed yellow, YiBriBoD-.p-.R;
Pink-eyed yellow, YiBr-.D-.p-AiR;
Pink-eyed yellow, YtBriD.piR.

The eyes of the two varieties last named contain only a small number of granules, all of
which are brovvn. They are indistinguishable from the eyes of the first two varieties,
which, however, contain black granules. The following description will serve for all
four varieties:

Eyes clear deep pink. Ears pink and unpigmented. In every other way these pink-eyed
types resemble closely the dark-eyed yellow types. They occur in all grades from a
deep orange to light cream, as do the dark-eyed forms. Because of the reduction of
black and brown granules sooty pink-eyed yellows are seldom if ever obtained.

Pink-eyed yellow x pink-eyed yellow, giving only intense pink-eyed young.
Cross 188. Giving pY, pBAg, and pB.

Mating.

Parents.

pY.

pBAg.

pB.

p?

155
195
160
173
113

1066 X 1064..
801 X 1064..

1067 X 1064..
1074x563. ..

562 x 563 . . .

3

2
2
2
6

5

1
3

2

2

i

2
1

15

9

4

4

Pink-eyed yellow x pink-eyed yellow, giving intense and dilute pink-eyed young.
Cross 189. Giving pY, pdY, and pdB.

Mating.

Parents.

pY.

pdY.

pdB.

468

Unmarked x 4523

1

1

1

Pi)ik-eycd yellow x pink-eyed dilute yellow, giving intense and dibtte pink-eyed young.
Cross 190. Giving pY, pdY, pB, and pdB.

Mating.

Parents.

pY.

pdY.

pB.

pdB.

pB or pdB.

p?
2

351

2342x2343... 13

1

4

2

3

98

THE INHERITANCE OF COLOR IN MICE.

Pink-eyed yellow x black agouti, gimng intense dark-eyed and pink-eyed young.
Cross 191. Giving Y, pY, BAg, and B.

Mating.

Parents.

Y.

pY.

BAg.

B.

Dark-eyed.

126

414x563..

8

1

5

5

2

Pink-eyed yellow x dilute black, giving intense and dilute dark-eyed and pink-eyed young.
Cross 191a. Giving Y, pY, B, dB or dBAg, pdBAg.

Mating.

Parent.s. Y. pY.

I

B. \dB or dBAg. \pdBAg.

p?

254

685x1435 1

2

3

1

3

1

Pink-eyed yellow x brown, giving intense dark-eyed young.
Cross 192. Giving Y and BAg.

Mating.
201

Parents.

Y.

BAg.

1489x1437...

5

3

Pink-eyed yellow x pink-eyed black agouti, giving only pink-eyed intense young.
Cross 193. Giving pY and pBAg.

Mating.

Parents.

pY.

pBAg.

p?

79
167
157

413x412

1062x1065

1060x1065

16

• ■
3

14
4
4

3

19

22

3

Cross 194. Giving pY, pBAg, and pB.

Mating.

Parents.

pY.

pBAg.

pB.

102

557 x563

23

8

2

Pink-eyed yellow x pink-eyed brown agouti, giving only pink-eyed intense yoking.
Cross 195. Giving pY and pBAg.

Mating.

Parents.

pY.

pBAg.

194

1395x1441...

3

2

RESTRICTED SERIES.

Pink-eyed yelloxo x pink-eyed black, giving only intense pink-eyed young.
Cross 196. Giving pBAg and pY?

99

Mating.

Parents.

pBAg.

237

684x763

3

In the following crosses the yellow parents would fall into one of the four following classes:

Pink-eyed dilute yellow, YiBriBidiPiA-iR;
Pink-eyed dilute yellow, Y ■iBr-iBidip-iR ;
Pink-eyed dilute yellow, YiBiYkp^AoR;
Pink-eyed dilute yellow, YiBvidiPiR.

These four types, as in the intense pink-eyed forms, are indistinguishable from one

another by superficial examination.
Eyes pink, otherwise indistinguishable from the dark-eyed dilute yellows already described.

No case of a pink-eyed dilute sooty yellow has been recorded in these experiments.

Pink-eyed dilute yellow x dilute black agouti, giving dilute dark-eyed and dilute pink-eyed young.
Cross 197. Giving dY, pdY, dBAg, pdBAg, dB, pdB, dBrAg, and dBr.

Mating.

Parents.

dY.

pdY.

dBAg.

pdBAg.

dB.

pdB.

dBrAg.

dBr.

pd?

435
425
436

Unmarked X 2488.

3493x2488

3490x2488

3

1
4

5
3
4

2
1

1

1
1
3

1

4
3

1

1

1

8

12

4

5

1

7

1

1

1

Pink-eyed dilute yellow x black, giving intense and dilute dark-eyed and pink-eyed young.
Cross 198. Giving Y, pY, pdY, B, pB, and dB.

Mating. Parents.

Y.

pY.

pdY.

B.

pB.

dB.

p?

389 2345x2343

4

5

1

4

3

2

1

We may now consider a few tests of albinos which have been made. All of these seem to
show that albinos may be potentially any of the 32 color varieties already mentioned
or any of their heterozygous combinations. None of the following albinos were tested
for dilution and therefore they are treated as intense in their formulie, though if the
proper test was made they might not turn out so.

100

THE INHERITANCE OF COLOR IN MICE.

Cross 199.

Albino X pink-eyed hroivn.

Mating.

517
536

458
540
466
518
498
470
516
497
478
508
505
429
578

Parents.

Unmarked x unmarked

4871 x-07

Unmarked x 440

4873 x-07

4870-73 x-07

4870 X unmarked

4870 x-07

4272x5162

4285-72x5162

4872 x-07

4273x5163

4285x5162

4271x5163

4408 X 3746

Unmarked x unmarked

2
2

B.

4
3
4
3

BrAg.

Br.

8
7
6
1
9
3
1
6
5
1

2

j)B.

pBrAg. \ pBr.

8
3
5

Formula of
albino parent.

BnDiPi.
BroDoPi.
BnD^Pi.
BriBDiPi.
Bi-iBD^Po.
Br.BDiPi.
BvoBDiPi.
3 Br^D^Pp.

6 BtoDoPpA .

2 Br-iBDiPp.

7 BriD-iPiA.

3 Br.,Dip.A.

. . i BfiD-iPiAi.
. . ' Br.D.P^R.
Br-iBDiP^AR.

A small number of more accurate tests of albinos follow:

Albinos X pink-eyed diltiie brown.
Cross 200.

Mating.

Parents.

dBr.

614
626

Unmarked x 7551 albino

Unmarked x 7868 albino

4
18

22

Both 7551 and 7868 albinos turned out potentially homozygous dilute brown animals.
Two crosses between homozygous dilute brown animals carrying albinism, and 7868 albino,
together with another albino (7748) of similar constitution, follow;

Cross 201.

Mating.

Parents.

dBr.

1
W.

628
637

7749 dil. br. x 7748 albino. .. .
7677 dil. br. x 7868 albino. . . .

6
2

4

7

8

11

The expectation is equality of white and dilute brown young.

The following case may in one sense be considered as unconformable. It seems probable,
however, that the animal recorded as yellow was a dilute form, for the experiment
occurred early in the series (1907) before I had learned to recognize dilute animals by
sight when young. This animal did not live more than two weeks and could not there-
fore be tested by breeding.

Pink-eyed black agouti x brown.
Cross 202.

Mating.

Parents.

Y?

BAg.

B.

77

415x409....

*1

3 1

*Probable incorrect classification.

BIBLIOGRAPHY. 101

BIBLIOGRAPHY.

Allen, G. M., 1904. The heredity of coat color in mice. Proc. Am. Acad. Arts and

Sci., vol. 40, No. 2, pp. 61-163.
Bateson, W., 1903. The present state of knowledge of colour-heredity in mice and rata.

Proc. Zool. Soc, vol. 2, pp. 71-78.

1909. Mendel's principles of heredity. Cambridge (Eng.) University Press, 396 pp.

Castle, W. E., 1905. Hereditj^ of coat characters in guinea-pigs and rabbits. Carnegie

Institution of Washington Publication No. 23, 78 pp., 6 plates.

1906. Yellow mice and gametic purity. Science, N. S., vol. 24, pp. 275-280.

1907a. On a case of reversion induced by cross-breeding and its fi.xation. Science,

N. S., vol. 25, pp. 151-153.
19076. Color varieties of rabbits and other rodents, their origin and inheritance.

Science, N. S., vol. 26, pp. 287-291.
1909. Studies of inheritance in rabbits. Carnegie Institution of Washington Pub-
lication No. 114, 68 pp., 4 plates.
1912a. On the origin of a pink-eyed guinea-pig with colored coat. Science, N. S.,

vol. 35, pp. 508-510.
1912?>. On the origin of an albino race of deer-mouse. Science, N. S., vol. 35,

pp. 346-348.

1912c. The inconstancy of unit characters. Am. Nat., vol. 46, pp. 351-362.

1912d. On the inheritance of the tri-color coat in guinea-pigs and its relation to

Galton's Law of Ancestral Heredity. Am. Nat., vol. 46, pp. 437-440.
Castle, W. E., and Little, C. C, 1909. The peculiar inheritance of pink eyes among

colored mice. Science, N. S., vol. 30, pp. 313-314.
1910. On a modified mendelian ratio among yellow mice. Science, N. S., vol. 32,

pp. 868-870.
Castle, W. E. and MacCurdy, H. (See MacCurdy, H.)
Crampe, 1883. Zuchtsversuche mit zahmen Wanderratten, Landwirths. Jahrb., xii, p. 389.

1884. Second paper, Landwirths. Jahrb., xiii, p. 699.

Cuenot, L., 1902. La loi de Mendel et I'heredite de la pigmentation chez les souris. Arch.

Zool. Exp. et Gen. [3], vol. 10, Notes et revue, p. xxvn.

1903. 2me note. Arch. Zool. Exp. et Gen. [4], vol. 1, Notes et revue, p. xxxiii.

1904. 3me note. Ibid., Notes et revue [4], vol. 2, pp. xlv-lvi.

1905. 4me note. Ibid., Notes et revue [4], vol. 3, pp. cxxiii-cxxxii.

1907. 5me note. Ibid., Notes et revue [4], vol. 5, p. 1.

1908. 6me note. Sur quelque anomalies apparentes de proportions mend^liennes.

Ibid. [4], vol. 6, Notes et revue, pp. vii-xv.
1911. 7me note, Les determinants de la couleur chez les souris, dtude comparative.

Ibid., Notes et revue [4], vol. 8, pp. xl-lvi.
Dakbishire, a. D., 1902, 1903. Notes on the results of crossing Japanese waltzing mice

with European races, Biometrika, ii, pp. 101-104. Ibid., pp. 165-173, pp.

282-285.

1904. [Second paper], Biometrika, iii, pp. 1-51.

Davenport, C. B., 1904. Color inheritance in mice. Science, N. S., vol. 19, pp. 110-114.
Doncaster, L., 1906. On the inheritance of coat colour in rats. Proc. Camb. Phil. Soc,

vol. 13, pp. 215-227.
Durham, F. M., 1908. A preliminary account of the inheritance of coat colour in mice.

Rep. Evol. Comm., 4, p. 41.
• 1911. Further experiments on the inheritance of coat colour in mice. Journ. Genet.,

vol. 1, pp. 159-178.
East, E. M., and Hayes, H. K., 1911. Inheritance in maize. Conn. Agri. Exp. Station,

Bull. No. 167.

102 THE INHERITANCE OF COLOR IN MICE.

GoRTNER, R. A., 1911a. Studies on Melanin IV. Am. Nat., vol. 45, pp. 743-753.

19116. On Melanin. Biochem. Bull., vol. 1, pp. 207-215.

GuAiTA, G. von, 1898. Versuche mit Kreuzungen von verschiedenen Rassen des Hausmaus.

Ber. Naturf. Ge.s. Freiburg, Bd. 10, p. 317.
1900. Zweite Mitthcilung iiber Versuche mit Kreuzungen von verschiedenen Rassen

des Hausmaus. Ibid., Bd. 11, p. 131.
Hurst, C. C, 1905. Experimental studies on heredity in rabbits. Linn. Soc. Journ. Zool.,

vol. 29, p. 283.
Keeble, F., and Armstrong, E. F., 1912. The role of oxydases in the formation of the

anthocyan pigments of plants. Journ. Genetics, vol. 2, No. 3, pp. 277-306.
Little, C. C., 1911a. The "dilute" forms of yellow mice. Science, N. S., vol. 33, pp.

896-897.
19116. The influence of heredity and of environment in determining the coat colors

in mice. Science, N. S., vol. 34, p. 563.
1912. Yellow and agouti factors in mice not associated. Am. Nat., vol. 46, pp.

491-493.
MacCurdy, H., and Castle, W. E., 1907. Selection and cross-breeding in relation to the

inheritance of coat-pigment and coat-patterns in rats and guinea-pigs.

Carnegie Institution of Washington Publication No. 70, 50 pp., 2 plates.
Morgan, T. H., 1911a. The influence of heredity and of environment in determining the

coat color in mice. Annals N. Y. Acad, of Sci., vol. 21, pp. 87-117, 3 plates.
19116. An attempt to analyze the constitution of the chromosomes on the basis of

sex-limited inheritance in Drosophila. Journ. Exp. Zool., vol. 11, pp. 365-412,

1 plate.

1911c. Moulting and change of color of coat in mice. Science, N. S., vol. 34, p. 918.

MuDGE, G. P., 1908a. On the hereditary transmission of certain coat characters in rats.

Proc. Roy. Soc, Series B, vol. 80, pp. 97-121.

19086. [Second paper, same title.] Proc. Roy. Soc, Series B, vol. 80, pp. 388-393.

1909a. Note on the chemical nature of albinism. Proc. Physiol. Soc, March 27,

p. LXVII.

19096. Further note on the chemical nature of albinism. Proc Physiol. Soc,

October 23, p. xvii.
Plate, L., 1910. Die Erbformeln der Farbenrassen von Mus musculus. Zool. Anz., vol. 35,

No. 20, pp. 634-640.
Riddle, O., 1909. Our knowledge of melanin color formation and its bearing on the

Mendelian description. Biol. Bull., vol. 16, pp. 316-351.
Sturtevant, a. H., 1912. Is there association between the yellow and agouti factors in

mice? Am. Nat., vol. 46, pp. 368-371.

LITTLE

PLATE 1.

w-

4

1. Wild type Black Agouti (Mus musculus), YBrBDPA

2. Dilute Black Agouti, YBrBdPA.

3- Pink-eyed Black Agouti, YBrBDpA.

4. Pink-eyed dilute Black Agouti, YBrBdpA.

A MOfN &C0. BALTIMORE.

LITTLE

PLATE 2.

^

J

7

>.

i.

8

"i—

5. Brown Agouti, YBrDPA.

6. Dilute Brown Agouti, YBrdPA.

7- Pink-eyed Brown Agouti, YBrDpA.

8. Pink-eyed dilute Brown Agouti, YBrdpA.

A,«OEN»CO BALTIMORE.

LITTLE

PLATE 3.

10

^^•S*^^t:.^--

m

11

;>t>Ww.,.

J^'"
f-^^

12

g. Black, YBrBDP.

lo. Dilute Black, YBrBdP.

I 1. Pink-eyed Black, YBrBDp.

12. Pink-eyed dilute Black, YBrBdp.

A.HOENaCO BALTIMORE

LITTLE

PLATE 4.

13

14

^'-**««^,__

f.

•^^V^m^Sfmi^H^

15

I

^-.^■^Sf .

m

16

13. Brown, YBrDPr.

14. Dilute Brown, YBrdP,

15. Pink-eyed Brown, YBrDp.

16. Pink-eyed dilute Brown, YBrdp.

A.HO£N a CO 9ALTIM0RE

LITTLE

PLATE 5.

n

i

17

.^.

19

m--

17. Black-eyed Cream (Yellow), YBrBDPR.

18. Brown-eyed Yellow, YBrDPR.

19. Dilute Brown-eyed Yellow, YBrdPR.

20. Sooty Yellow, YBrDPR.

AHoewaco Baltimore,

MB) WHOI IIBHARV

WH IflET F

3 U 7