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AN ANALYSIS OF THE EFFECTS OF SELECTION

By A. H. STURTEVANT

/49/(76

DO By

PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON
WASHINGTON, 1918

CARNEGIE INSTITUTION OF WASHINGTON

PusiicaTion No. 264

PRESS OF GIBSON BROTHERS
WASHINGTON, D. C.

STURTEVANT PLATE 1

1. Dichaet male (5-bristled) 2. Extended female. 3. Wild-type female.
(Drawings by Miss E. M. Wallace. )

ANANALYSIS OF THE EFFECTS OF SELECTION.’

INTRODUCTORY SUMMARY.

The present paper describes a series of experiments aimed at de-
termining the causes of the variability in bristle number observed in
Dichet, a mutant race of Drosophila melanogaster (ampelophila).
These experiments are discussed under several headings, as follows:

(a) Selection of plus and of minus variants was carried out. Both
plus and minus lines were obtained and were used in the further ex-
periments.

(6) A plus line and a minus line were crossed, and an increase in
variability was observed in F».

(c) Linkage tests were made, and by this means it was demon-
strated that modifying genes were present in the selected lines.

(d) Evidence against the hypothesis of contamination of allelo-
morphs was obtained.

(e) This evidence, and that obtained by other investigators, is then
utilized in a general discussion of the selection problem, and of the
hypothesis of contamination of genes. The conclusions are drawn
that selection is usually effective only in isolating genetic differences
already present; and that genes are relatively stable, not being con-
taminated in heterozygotes, and mutating only very rarely.

DICHAT.

The mutant character known as Dichet was discovered by Dr.
C. B. Bridges, July 3, 1915. In an experiment involving the sex-
linked characters sable, forked, and cleft there appeared a single
female that had wings extended and bent backwards near the base,
like those of the mutant bent (Muller, 19146). In addition it was
observed that this female had only 2 dorso-central bristles, instead
of the 4 usually present. When mated to a male having the mutant
character eyeless, this female produced 48 normal offspring and 46
“Dichet,” thus showing the character to be dominant.

Bridges’s unpublished data show that the Dichet gene is in the third
chromosome, approximately 5 units to the left of pink.

The data published by Muller (1916) give the locus as 9.7 from sepia
(the locus farthest to the left of those as yet discovered), and 11.0
from spineless, on the right. My own (unpublished) data give:

Sepia Dichet, was 14.9 p. ct. Dichet spineless, a = 13.1 p. ct.

1369 1

1J am indebted to Mr. J. W. Gowen for much advice and assistance in connection with the
statistical treatment of the present problem. He has done a part of the actual calculations,
but is not responsible for any arithmetical slips, as I have myself done all the checking.

3

4 AN ANALYSIS OF THE EFFECT OF SELECTION.

The averages, roughly weighted according to number of individuals,
are: sepia Dichet, 13; Dichet spineless, 12. This agrees with the
data of Bridges on the position of Dichet with reference to pink, since
that locus is about 8 to the left of spineless.

Bridges also found that homozygous Dichets are not produced.
The gene, like that of the yellow mouse, acts as a lethal when homozy-
gous. The result is that when Dichets are mated together they
produce two heterozygous Dichxts to one not-Dichet. This dis-
covery has been verified by the experiments described in this paper,
and by other experiments carried out by Muller and by the author.

TABLE 1.
No. of bristles.
Culture
Brot 3 taal eel ees
881 9 | 20 | 27
882 1 | 23 | 29 | 30
883 9] 11] 11
900 32,522.) 13
2715 7| 15] 3
1 | 80 | 97 | 84
Fics. 1 and 2.—Two types of bristle distribution
in Dichets—a ‘‘3"’ and a ‘7."" Small post-alars are 2 and 7 bristles have also been ob-
present in fig.2. ‘These are never counted in the totals. served in unselected stocks.

As shown in plate 1, fig. 1, the wings of Dicheet flies are held out from
the body and are bent back near the base. The number of dorso-
central bristles (on the dorsum of the thorax) on the original female
was 2 instead of 4, as is usually the case in the normal fly (plate 1,
figs. 1 and 3). This has since been found to be a variable character.

The number of dorso-centrals varies from 0 to 4, and sometimes
one or more of the scutellars may be missing. In addition, the an-
terior post-alars above and just behind the wing-base are reduced or
absent. Plate 1, figure 1, and text-figures 1 and 2 show some common
types. The work reported in this paper has consisted in selecting for a
high and for a low total of scutellar and dorso-central bristles. Counts
from five unselected cultures gave the results as shown in table 1.

The normal flies occasionally show variations in bristle number,
but these are much rarer than in the case of Dichet. MacDowell
(1915) has given some data on the frequency of these variations, and
has also reported on very extensive selection experiments with them
(1915, 1917). These experiments will be referred to below.

I have made bristle counts on a few unselected not-Dichzt stocks,
with the results shown in table 2.

The normal flies have 8 dorso-central and scutellar bristles in most
cases, while the Dichets range from 1 to 8. But the 8-bristled Dichets
are still distinguishable from normals, even when their wings are not

AN ANALYSIS OF THE EFFECT OF SELECTION. 5

unfolded enough so that they can be separated on that basis. This
is because the anterior pair of dorso-centrals never, so far as I have
observed, becomes as large as the corresponding pair in normal flies.
The anterior post-alars are also reduced in 8-bristled Dichets. This

TABLE 2.
6 7 8 9 10
Stock. a Total.
OM alee lo, ie} fou | Htott| [takedan bilve?

Wild:
Falmouth, Massachusetts.| 0/| 0]} O 1 | 186 | 118 | 11 2 Ovo 318
Berkeley, California. ..... 0 0 0 0 95 | 104 0 0 0 0 199
Mitchell, South Dakota...| 0 0 0 OF |) 226.213) 4 1 0 0 444
Amity. \Oregonit 1. cie a0 0 0 0 0 59 51 1 1 0 0 112
Sydney, Australia......... 0 0 0 0 16 21 0 1 0 0 38
Pinksbandle nics istic tssataee 0';) 0 1 5 | 103 | 99 1 03), Oy, 0 209
IBlackacs teeter nce OFF 30" | OTP Oee 26738) sO" rye t0y' 0 64
IMDONY,.:a- dawellact noekiten ee OUP OL: ON On eRSOne 92) BON On eOut) O 172
Blistered 5.5 Mc.c scr aysteaceua ies Oc On LON On 4 67 | OMe On Oot eO 181
NWihhitelcrestors stetuselemre eters tier OP 0! | POO). | ee: ee 2a TOP I One 0 153

separability is a matter of some importance, since, because of the
lethal effect of Dichet, any Dichet culture may produce normal
flies. However, the spread wings can be and are used for the separa-
tion in all but the rather rare instances of failure to expand properly.

SEXUAL DIMORPHISM.

Calculations show that there is a slight but significant sexual di-
morphism in bristle number in the Dichet races. Random selection
of plus and of minus selected cultures gave the totals shown in table 3.

TABLE 3.
Bristle number.
Total.
1 2 3 4 5 6 of 8

Tei Bois ollGanilodas 4 490 | 668 | 1,702 | 81 | 6] 2,951
IAT Wropee Elia ole ei|| er say 436 | 684 | 1,527 | 53 | 8 | 2,736
Minus 9..|...| 5 TL OLT | 712 424 | 7 |...| 2,682
Minus o’..| 1 | 39 | 177 | 1,190 | 615 332 | 2]|...| 2,356

These distributions give the statistical constants shown in table 4.
The first three columns show that there is a slight difference in the
means, the females being higher in both cases. In the case of the plus
series the difference is doubtfully significant; in the minus series it is
larger and certainly significant. The last column gives the chance

6 AN ANALYSIS OF THE EFFECT OF SELECTION.

that differences as great as those observed between the two distribu-
tions are due to random sampling. These values were obtained by
Pearson’s x” method (Pearson, 1911). This column makes it quite
certain that there is a significant sexual dimorphism in both series,
and also brings out again the fact that the dimorphism is greater in
the minus series.

TABLE 4.

co Mean. Difference.

Plus 5.468+0.010 | 5.428+0.010 | 0.041+0.014 | 0.0001
Minus...) 4.583 .010 | 4.436+ .012 147+ .016 - 0000000 +

Because of the information given by this table it has seemed de-
sirable to present the data for males and females separately. This
has been done in the Appendix; but since the dimorphism is slight,
the data have been lumped in the statistical treatment given in the
body of the paper. The data in the Appendix make it possible to re-
calculate the constants separately if it should seem desirable to do so.

EFFECTS OF ENVIRONMENT.

In any selection experiment it is obviously very important to have
some information regarding the influence of environmental conditions
on the variable character used. If the observed variations in the
character are largely due to environmental causes, it should be very
difficult to accomplish much by selection; but if the environment
plays little part in causing variability, selection should be very effective
in isolating different types, and on the multiple-factor view variability
should show a marked decrease after a few generations of inbreeding.

In the case of Dichet, it has been observed that as cultures grow
older the flies frequently have fewer bristles. In such cultures it is
usually observed that the later flies are also smaller and that the food
conditions in the bottle have become unfavorable. It is, therefore,
essential in such experiments that conditions be made as nearly uni-
form as practicable.

The data in table 5 show that under ordinary conditions there is
considerable environmental effect. Eight pairs from the regular series
were transferred to second bottles, after staying the usual period in
the first one. Offspring were thus cbtained with identical pedigrees
and differing only in that they were reared in separate bottles. No
attempt has been made to make conditions different in the two bottles,
which constitute a random sample of the conditions under which the
experiments were carried out. Table 5 shows the results obtained.
(The actual data are in the Appendix; the first three columns of the

AN ANALYSIS OF THE EFFECT OF SELECTION. 7

table will enable the reader to find them.) The last three columns
give the results of an application of the x? test to the data. The last
column, headed P, gives the chance (1.0 representing certainty) that
deviations from identity as great as those observed could have re-
sulted from random sampling. It follows that in at least three cases
(the fifth, sixth, and seventh) the results given by the two broods were
significantly different.

TaBLE 5.—First and Second Broods from Same Parents.

Culture Nos. Genes

ations a ;
mother P
inbred.

Series.
First | Second
brood. | brood.

1,907 Noe) Tesi spadonasaddes 4 3.74 | 3 | 0.16
1,908 15997 |) L002 rev iea2e =f 6 5.60 | 5 -23
1,912 Ute || LE UPRE on oc began 7 2.10
7
9

4 55
POZE | L909" | LOO rer. -tsrcciereietse 6.05 | 5 19
ZAOTAA S251 400 | OOO Tawa siteektss sate 22.09 | 4 -0001
2,078 | 2,141 | Test of crossbr. plus.| 11 16.81 | 4 -001
2hOST |" 2h LAT SG4 ee Mek a cterciers 6 11 19.80 | 5 0005
2,475 | 2,518 | Test of 1002........ 118 5.22 | 3 075

1F\, and F\7 were mass cultures in this case.

There is one possible source of error in these data: It has been
shown by Bridges (1915) that the amount of crossing over in the sec-
ond chromosome of Drosophila varies with the age of the female.
My own unpublished data show that this is also true for the third
chromosome. In the present case, if the female parents of the flies
observed were heterozygous for many modifying factors, such a
change in linkage might result in the production of genetically differ-
ent first and second broods. However, the female parents in these
cultures were in every case from at least four generations of brother-
sister inbreeding (see table 5, column 4)! and in the significant cases
for 9 and 11 generations. It is therefore very unlikely that they were
heterozygous for many modifying factors. The two broods from
these females must, then, be of the same genetic constitution, and the
differences between them can only be due to environmental causes.
It follows that in the experiments recorded below a significant part
of the variability is not genetic, but environmental.

METHODS.

With very few exceptions, the flies recorded in this paper were bred
from pairs, and in pint milk bottles. The food used was ripe un-
cooked banana, fermented in a stock yeast-culture for from 12 to 48

1Three cases in which the female parents were hybrids have been discarded (see 2091-2143,
3064-3116, 3066-3118 pairs in Appendix).

8 AN ANALYSIS OF THE EFFECT OF SELECTION.

hours (usually about 24 hours). Paper toweling was added to absorb
surplus moisture.

The experiments were begun in New York City in February 1916,
and were carried on there until the middle of June, when the material
was moved to Woods Hole, Massachusetts, and continued there until
the end of September. All these flies were kept at room temperature.
The work was resumed in November, in New York, and continued
until the middle of May 1917. During these last six months the
flies were reared in a heated case that was regulated by a thermostat,
so that the minimum temperature was about 24°, the maximum being
about 26°, except when room temperature went a few degrees higher,
as occasionally happened. It is to be noted that the constant-tempera-
ture series run more evenly (see especially 1002 line), thus suggesting
that temperature influences bristle number.

In order that the data presented in the Appendix may be correlated
with this information, if it seems desirable to do so, the following
table is presented. Each culture received a serial number at the time
the parents were mated, and these numbers run consecutively through-
out all the author’s recent experiments (on other problems as well as
selection). These serial numbers are recorded in the Appendix.
Therefore, it is possible to fix approximately the date on which a cul-
ture was made up, if we know the date on which a culture with a simi-
lar number was made up. The dates of all cultures are noted on the
record sheets, but it has seemed hardly necessary to present more than
the following ‘‘landmarks.”’

TABLE 6.
Culture. Date. Culture. Date. Culture. Date.
884 Feb. 3, 1916 1507 June 7, 1916 2389 Sept. 16, 1916
1006 Mar. 24, 1916 1617 June 23, 1916 2423 Nov. 18, 1916
1100 Apr. 16, 1916 1830 July 14, 1916 2601 Jan. 13, 1917
1150 Apr. 22, 1916 2000 Aug. 1, 1916 2950 Mar. 17, 1917
1301 May 15, 1916 2250 Aug. 28, 1916 3078 Apr. 15, 1917
1401 May 28, 1916
SELECTION.

If the variations observed in the Dichet character are due to modi-
fication of the Dichset gene itself, selection should be as effective in
inbred stocks as in any other kinds. If multiple factors are responsible
for the variations, the method of breeding should affect the result.
If a stock is closely inbred while being selected, it will soon become
fairly uniform, so that selection should be effective for only a com-
paratively short time. But if a strain is subjected to some crossing
it will become uniform more slowly, so that selection should be effective

AN ANALYSIS OF THE EFFECT OF SELECTION. 9

longer. Moreover, there is a chance of combining more of the desired
modifiers in the same individual when crossing is done, so that this
method might produce more extreme results than the inbreeding
method. However, each time a cross is made some of what has been
gained may be hidden by dominants in the other stock; therefore
progress might sometimes be slower.

Accordingly, in these experiments parallel series have been carried
on. In one set selection has been accompanied by continuous brother-
sister matings; in the other, frequent crosses have been made between
individuals more or less closely related. 'The same method has been
followed in both the plus and the minus selected lines. The four
series will be considered in order: (1) inbred plus; (2) crossbred plus;
(3) inbred minus; (4) crossbred minus.

INBRED PLUS SERIES.
Two main lines of this series have been carried on. A few cultures

have been made from other sources, but none of these are sufficiently
extensive so that we need follow their histories here.

864 Line.
Culture 864, from which this line arose, was produced by a female
{/

To
p’s.ke'r,
the sepia, spineless, kidney, sooty, rough stock; 847 was the result of
mating four peach, spineless, kidney, sooty, rough males from stock to a

/

of the constitution from culture 847, and two males from

. . r .
female of the constitution mee F This female ane
3 Dorso- A
was descended from the Dichet, ebony, peach, centrals, | Oflspring.

spineless, kidney, sooty, rough, and other stocks.
Her pedigree is not now traceable in detail.

At the time culture 864 was counted, the scu-
tellar bristles were not observed. The dorso-
central bristles were recorded on 30 flies, as
shown in table 7.

The 3 (almost certainly a 7, according to the system later adopted),
a male, was mated to a 2 (6) female to produce culture 893. For the
details of the remainder of the pedigree see Appendix.

In the accompanying tables and curves the offspring of culture
893, above, are considered F;. Table 8 gives the data for this line
summarized by generations. In this and the following tables, n is
the number of individuals in the generation, M is the mean bristle-
number of the generation, ¢ is the standard deviation, r is the parent-
offspring correlation, and is recorded in the generation to which the
offspring belong. Diff. M. is the mean bristle-number of the off-
spring minus the mean bristle-number of their parents, weighted

12
8
9
1

30

10 AN ANALYSIS OF THE EFFECT OF SELECTION.

according to number of offspring, and is also recorded in the offspring
generation. In the calculation of r, the parental grades are taken as
the average grades of the two parents. When r is not given, it is not
capable of calculation, for the reason that all parental pairs in that
generation were of the same average grade. The correlation coeffi-
cients given here are of doubtful significance, though many of them
are several times their probable errors. These probable errors, like

Taste 8.—S864, Inbred Plus Line.

Generation. n M o r Diff. M.
Bigsceve sect 113 1852672 0.048 1/50.-762==OKOS45| eeieclereieterersor cere —0.828
Wiss ciasciayeiashne 121 | 5.331+ .049 1804.2 OSB IRs -rtsyatars) «toherpsrale —1.179
Bgiiete tetera: 73 | 5.822= .031 O90 se sO | sista ave sterate eieveiave — .178
IV Esasn coun 260 | 4.904+ .036 SSO8 ==) OZGe)|| (<5) «10e areis or stsielels —1.016
Bigeye caevereesle 149 | 5.228+ .043 SGML tir OSO ni i covstiisveversueuanctotctons — .772
Rice sucusvesg ails 120 | 5.450+ .044 SOB HS) esOSle ll si cfevsisiase stay scs tenet — .550
Repke citoraete 510 | 5.190 .025 S880 se) OLS: | Perens score eee — .810
ig ek tey.. eoe 461 | 5.475+ .023 .738+ .016 | +0.105+0.031 | — .514
Big sicrecusicve (8 154 | 5.6434 .034 621+ .024 | + .002+ .054 | — .458
Bygi ete cee 159 | 4.956 .051 EQGO==) ROSEN! tase seecoe tee —1.044
tages tsetse 232 | 5.224+ .039 .867+ .027 | — .011+ .044 | — .901
Wigs caveat 624 | 5.272+ .025 BOSSE) OLS all cetera stare tere stshenees — .728
Bisco ay austere 353 | 5.787+ .024 .667+ .017 | — .070+ .036 | — .762
Brant: scien 175 | 6.080+ .026 506+ .018 | + .133+ .050 | — .300
3,504
REVERSED SELECTION.
ieee ess 33 | 5.152+0.102 | 0.869+0.072 | ..:..........- +0.652
Fy. . 49 | 5.327+ .092 SO56= SSOGON |leeveretese) ocusteetesaret- +1.329
Bua giteaessteresexe 62 | 5.710+ .052 AGNES WEST Il madgcbacooodGce +1.710
144

others of their kind, are intended only to give the magnitude of the
error likely to arise from the fact that one is dealing with a sample of
limited size—the error of random sampling. But in the present case
the correlation coefficient is intended to measure the similarity be-
tween the somatic appearance and the genetic possibilities of the
parent individuals. It is known that this similarity does not amount
to identitv, and that it may be modified in individual cases by en-
vironmental causes. Since in any given case we are dealing with a
rather small number of parent individuals, but a large number of off-
spring individuals, the selection of one or two parents whose somatic
appearance differs widely from their genetic possibility will throw
the resulting correlation coefficient far off; but the large number of
offspring will keep the probable error down. If, instead of entering
each offspring individual in the correlation table separately, we enter
only the mean grade of the offspring of each parent pair, we get what
is perhaps a more reasonable probable error. But this method fails

AN ANALYSIS OF THE EFFECT OF SELECTION. fe

to weight the results from different parents according to the number
(and therefore reliability) of their offspring. In the present case,
also, it gives an extremely large probable error, and probably gives a
less accurate value for the coefficient itself. The usual method has
accordingly been followed, but little reliance is to be placed on the
biological significance of the results obtained. Hence in the follow-
ing discussion the correlation coefficients will be largely ignored.

7

27 Sera oe Ge gS) Oo NO Th es as 4

Fic. 3.—Means and standard deviations for 864 inbred plus line. The gener-
ation number is given on the abscissa; bristle number on the ordinate.
The dotted lines represent reverse selection.

The values for M and oa in the 864 line are plotted in figure 3.
Selection has apparently affected this line hardly at all. This is per-
haps because in the early generations so few individuals were bred
from. Reversed selection (dotted line in curve) was ineffective in
the eleventh to thirteenth generations, thus indicating again that at
that stage at least the line was not capable of modification through
selection.'

1002 Liner.

The second inbred plus line is descended from culture 1002. The
/

female in this culture was of the constitution and the four

S.s,ker,
males were from the peach, spineless, kidney, sooty, rough stock.

1The fact that the signs of the differences between the means are reversed when selection is
reversed is due simply to the fact that the parents selected are now below the mean of the line,
instead of above it. The difference between the means, like the correlation coefficient, is of
slight significance when the number of parent individuals is as small as in these experiments, and
for the same reasons.

12 AN ANALYSIS OF THE EFFECT OF SELECTION.

The female was from culture 916, which contained a sepia, spineless,
/

This female was the

offspring of a Dichet from stock and of a fly from culture 869 (q. v.
below, in the pedigrees of 900 and crossbred minus lines). No bristle
counts are available from culture 1002, except those of the pair (6X6)
selected to produce culture 1072, the F, of this line.

After this line had been inbred and selected for 11 generations, a
pair of 7-bristled flies were taken from 2389, and their descendants were
bred in mass cultures, unselected Dichets being mated together, for
about 2 generations. The line was then re-established by selecting
pairs from this stock and was inbred for 8 generations more.

The data and curves for this line are given in table 9 and figure 4.

kidney, sooty, rough male, and a female

) any ras Tike | 5 Gi tars ao pO LT I? (Oe Spree 0 enO ee

Fic. 4.—Means and standard deviations for 1002 inbred plus line.

Here selection was perhaps effective for a few generations. Ref-
erence to the Appendix will indicate that this effectiveness was prob-
ably due in large part to the gradual elimination of the descendants
of one of the F, pairs (1158), which were on the average of slightly
lower grade than those of the other F, pair (1150). It is to be observed
that both of the apparently successful reversed-selection series were
made with descendants of the former branch of the family.

The eighth to eleventh generations of this line and the contempo-
rary eleventh to fourteenth of the 864 line gave very similar results
as to the means and standard deviations. We shall see below (p. 19)
reason for believing that the two lines were of very similar constitution
at this period. The gradual rise of the means and fall of the standard
deviations is probably of environmental rather than genetic origin.

AN ANALYSIS OF THE EFFECT OF SELECTION. 13

The ‘‘new” series, which was carried on at a constant temperature,
shows remarkably little fluctuation. Of the two reversed-selection
series, one suggests a positive result, but was not carried on long

TasiLe 9.—1002, Inbred Plus Line.

Generation. n M o be Diff. M.
1 ane ae oc 114 | 5.0700.051 | 0.815=0-036 | ..............- —0.930
Boejocccinsicis 231 | 5.052+ .039 ESS == A O25M |i erefeictapitercacel ol aere — .948
Uap eacddae 446 | 5.473+ .025 .784+ .018 | + .157+0.031 | — .661
Watictti:stlelete 1,199 | 5.126 .018 .922+ .013 + .153+ .019 —1.113
Cae Soo 1,142 | 5.658 .014 .720+ .010 — .024+ .020 — .397
Recetas 632 | 5.389+ .022 .853+= .015 + .381+ .024 —1.029
Eizetehoal sietctess 283 | 5.675+ .027 .683= .019 — .805+ .036 | —1.127
Bat sb cle ee 584 | 5.202+ .023 .826+ .016 + .481= .022 | —1.122
igniayerisiciete 373 | 5.507+ .027 .763+ .019 + .205= .033 | — .690
Biotec sites 269 | 5.952+ .018 450+ .013 + .115= .040 | — .128
Baha veltoraieleves 133 | 6.158+ .026 .456+ .018 — .025= .058 | — .477

5,406

New set

eye sicisis 167 | 5.850+0.021 | 0.362+0.014 | !—0.038+0.046 | .......
iM enodor 447 | 5.978+ .011 .340+ .008 — .009+= .032 | +0.087
Lenooee 377 | 5.889+ .020 .563+ .014 + .048+ .034 | — .668
LOS naeee 79 | 5.886+ .031 .422+ .022 | 14 .1234 .042 | —1.114
DR gererictets 73 | 5.904 .046 .578= .032 | 1— .062+ .072 | — .096
Reticse'e.: 128 | 5.969+ .026 .429= .018 | T— .031+= .039 | .......
Bgevoveretes= 92 | 5.935+ .027 oS Leh OLD) |\iteyetovercycletersterscerereje —1.165
Bei ctinac 79 | 5.93874 .045 RSSA=EP SOSID |r yeincyeveis ovcievers — .063

1,442

REVERSED SELECTION.
pa vaystets i atere 62 | 5.339+0.085 | 0.989+0.060 | ............... +1.339
Wg er oh ste (s)sievots 46 | 4.652+ .089 BO90S= S063) ||rcrercteiin va «veinzies) ole + .652
Eyrisieis\ais.c¥ers\ 68 | 4.147+ .062 Oo BOLE ietescts cin eeeiaios “vo + .147
Wig nsyafereioicie'= 23 | 4.739 .119 A a5 OBA! IIIS ateyess ofoia <listalsia eter +1.239
izexsrsishazetelets 125 | 4.680+ .060 2993 ls O42) I eevee ayes) aric\sl= cle +1.180
New set

Rialeicteyalers 49 | 5.898+0.046 | 0.463+0.032 | ............... +0.898
etic cecie 13 | 6.000+ .000 SEDER AOE UA Sop pononc naasoc + .500
Bigs 5 cists 99 | 5.707+ .041 SEY ES: ollP+3al | Ryo nee momen os | | oeaenroS

485

1Includes reversed selection, that is, not included in the remainder of these data.

enough to be significant, and the other was clearly without effect.
The line was now presumably uniform, and not capable of modifica-
tion through further selection.

CROSSBRED PLUS SERIES.

The material for this series came from the following sources: Cul-
tures 902, 926, 1006, 1081 of the 864 inbred plus line; culture 1072 of

14 AN ANALYSIS OF THE EFFECT OF SELECTION.

the 1002 inbred plus line; 2 individuals (in cultures 937 and 1074)
from the Dichzt stock; culture 1004, which was made up from exactly
the same sources as 1002 (see above), and differed from that culture
only in that a single male was used.

This material was mated in various ways, but brother-sister matings
were practised infrequently, and then (see Appendix) not often in
successive generations. All the cultures in this set were descended
from the 864 inbred line; and the ‘‘generation”’ of each culture has
been taken as the greatest number of generations from 864 shown by
any line of the ancestry of that culture. This method is somewhat
misleading, since in every case the “‘generation’’ thus given is higher
than the average number of selected generations, and still higher than
the average number of crossbred selected generations in the pedigree.
For example, the first culture in the series, 937, is recorded as F3,
since the father came from the F, generation of the 864 line; but the
mother was an unselected individual from the Dichet stock. Cul-
ture 1074 is recorded as F;, though the father was unselected and the
mother was from the inbred 864 line. Culture 1254 is recorded as
F;, though one parent belonged to F;, and the only grandparent
not an F; came from 1074, above. This method of grouping the data
has been adopted because it is convenient to handle, and because it

TaBLe 10.—Crossbred Plus Series.

Generation. n M o r Diff. M.
Ba erau osene 53 | 5.283+0.079 | 0.856+0.056 | ............... —1.217
geno apecssciars 417 | 5.211 .028 ASSO BOZO ee oe cei terctapoiciale — .719
Ug ore sicusteisiere 812 | 5.489+ .018 779+ .013 +0.156+0.023 — .643
Bigereccisiateratene 1,031 | 5.790+ .012 599+ .008 + .027+ .021 — .772
| Ga Goae 1,006 | 5.7334 .015 -717+ .011 — .023+ .021 — .891
gett clashes 877 | 5.616+ .018 .790+ .013 — .086+= .023 —1.423
Bo ticirtas es 388 | 5.840+ .024 -711+ .017 — .147+ .034 —1.120
Bt Giageneieiersices 236 | 5.822+ .026 591+ .018 — .196+ .042 —1.589
4,820 |

is desirable for purposes of comparison and computation to have the
generations expressed in whole numbers. The errors involved all
tend to make it appear that selection has been applied longer than is
actually the case, and this should be borne in mind when studying
table 10 and the curve (fig. 5) for this series. The pedigrees may be
traced from the data in the Appendix, if anyone cares to make a differ-
ent classification.

Selection has apparently been successful in raising the mean of this
series; but this conclusion is not certainly correct, because of the en-
vironmental possibilities discussed above.

AN ANALYSIS OF THE EFFECT OF SELECTION. 15

INBRED MINUS SERIES.

As in the case of the inbred plus series, two lines were carried on
here. One of these was not kept long; but its history is given here,
chiefly because it was used in producing the crossbred minus line.

900 Line.

Culture 900 produced Dichet flies as shown in table 11.
This culture was produced by mating a male

from the sepia, spineless, kidney, sooty, rough en pies
eee Si Bristles. | Offspring.

stock to a female of the constitution - that

was obtained by inbreeding a pair of flies from 5 5

869 (see pedigree of 1002 inbred plus line). $ ey

869 was produced by a male from the sepia, | Total..... 67

spineless, kidney, sooty, rough stock and a fe-
male from 854, which came from 839 (?) and 840 (<7). 840 also
enters into the pedigree of the 868 line, below. 839 and 840 were
sister pairs, the males coming from the sepia, spineless, kidney, sooty,
rough stock, and the females being F, hybrids of the sepia, peach,
ebony, and Dichet stocks.

end OT ey

3 4 5 6 7 8 9 10
Fig. 5. Fig. 6.

Fig. 5.—Means and standard deviations for crossbred plus line.
Fic. 6.—Means and standard deviations for 900 inbred minus line.

Table 12 and the curve (fig. 6) for this line are arranged in the same
way as those for the inbred plus lines.

16 AN ANALYSIS OF THE EFFECT OF SELECTION.

The effectiveness of selection is doubtful, but the line runs con-
sistently lower than the three plus lines, and reversed selection was
perhaps effective.

TaBLE 12.—900, Inbred Minus Line.

Generation. n M o r Diff. M.
Bis s.cereieree 130) )|"4. 769 == 0.045. | Ot 71 ==ONOB2 Ih ieee ecsset crete si ener ioum +0.769
Ret aS eas, 204 | 4.603+ .038 NO OAS OZ Gallvoievouspeveelskegeus steneta + .603
Fig isysisiensirctaters 256 | 4.578+ .032 .767+ .023 — .021+ .042 | + .976
ig en ee 194 | 4.959+ .040 .818+ .029 + .155+= .048 | +1.000
1 ease Soe 243 | 5.124+ .037 .847+ .026 + .032= .043 | +1.255
Nes. sores Netave 103) |e. 6602] COZ Zal| MAG Sa ODS erste crereretereretetetslone + .660
Wi ives saheiess 148 | 5.000+ .044 .797+ .031 + .103= .055 | +1.986
Wertvstevasat 69 | 4.826+ .070 .867+ .050 + .159= .079 | — .420
Mga aes etosets 271 | 4.576+ .031 -740+ .022 — .005+ .041 | + .644
Hips sacs. 762 | 4.555+ .019 .769+ .014 — .0O11+ .024 | + .654
1 Ov ioeratars Oe 340 | 5.141+ .031 .849+ .022 — .142+ .036 | +1.340
2,720
REVERSED SELECTION.
1 OP St er 68 |4.897+ 0.062 |0.750+ 0.044 | ............... —1.103
Wii ccaicieve were 71 15.4512: 3062 | .7283= “O440\in irc ricites — .549
Regence one 98 |5.194+ .082 | .488%= .023 | ..........000.- — .806
237

868 Minus Line.
This line is descended from culture 868, which was produced by a

sepia, Dichet, ebony-sooty female from 856 and a rough male from
852; 856 was the result of mating a stock sepia, spineless, kidney,

sooty, rough male to a Dichet ebony-sooty Tamas
female from 840 (q. v. above, in pedigree of ;
900 line). 852 was a descendant of the peach, Dorso- | Ofspring.
spineless, kidney, sooty, rough, and peach- centrale.
ebony stocks, and (although it did not trace to 0 25
the Dichet stock) of the same original cultures 5 sf
as 864, the ancestor of the first inbred plus line 3 0
(see above). 4 £
The offspring of 868 itself were classified for | Total..... 51

dorso-central bristles, as shown in table 13.

The data for the succeeding generations are given in table 14 and
figure 7.

The numbers of individuals and of generations are rather small,
for the reason that the line was not very vigorous, and finally died
out in spite of all attempts to preserve it. It gave the lowest means
of any line so far discussed. Reversed selection was apparently suc-
cessful.

AN ANALYSIS OF THE EFFECT OF SELECTION. 17

TaBLE 14.—868, Inbred Minus Line.

Generation. n M o

re ie cere ier 74 | 4.432+0.070 | 0.888+0.049
Wgiera = chemteurs 109 | 4.688+ .053 -820+ .037
Bye sence 193 | 4.104+ .042 .834+ .029
Wg iwaiers estetere 68 | 3.765+ .063 -768+ .044
LY Reena ns 84 | 4.286+ .053 -716+ .037
eRe codas 22 | 4.228= .106 .736+ .075

550

REVERSED SELECTION.

le Oneesats 112 | 4.732+0.055 | 0.856+0.038
1 Dares BERG 225 | 4.862+ .039 -866+ .027
337

CROSSBRED MINUS SERIES.

The following cultures furnished the material for this series:

Cultures 920, 1063, 1073, 1082 of the 900 minus line.

Cultures 935, 936, 1047 of the 868 minus line.

Culture 942, made up by mating together two 4-bristled Dichets
from 912, which in turn was the result of mating a sepia, spineless,
kidney, sooty, rough male to a female from a daughter culture of
869 (see pedigree of 900 line).

: are. LNA
Culture 949, made up by mating a female of the constitution —-~———*

p?sseTo
(from the cultures of Mr. J. W. Gowen) to a male from culture 916
(see pedigree of 1002 line).

All the cultures in this series traced to 868, and the ‘‘generation”’
given is the greatest number of generations from 868, which is thus
the standard for this line, just as 864 was for the crossbred plus series.

Table 15 and figure 8 give the results for the series. Here again,
the effectiveness of selection is suggested, but is doubtful. The means,
however, are lower than in any other series except the 868 line, and
that line entered very largely into the make-up of this one.

Speck Minus or 1331 Line.

In connection with certain experiments to be described below it
became desirable to have a minus line that should be recessive for some
second chromosome character. Accordingly culture 1331 was made
up by mating a 4 female from 1168, Fs, of the crossbred minus series,
to a speck male.’ The line was then inbred, in pairs, brother to sister,
minus selected, and gradually made homozygous for speck, sepia, and
rough.

18 AN ANALYSIS OF THE EFFECT OF SELECTION.

ee
LE owt ‘56
Fic. 7.

Fig. 7.—Means and standard deviations for 868 inbred minus line.
Fic. 8.—Means and standard deviations for crossbred minus line.

Fic.

8.

TaBsiE 15.—Crossbred Minus Series.

Generation. n
gic 'x:atelavele,s ie 323
| Raa Go ae 688
Beene an 1,022
Baan iotetere tie 1,473
Be saiectctias 1,503
ge ccicariee 401
Bie ashore 265
Pere yetetereiey 245
Bio's susssye ava. 177
6,097

LAL __ PP PP

M

-523+0.028
-297+
667+
.357 +
622
354
-083 =
073
AT5 +

-020
.017
-013
-014
-025
026
-030
-039

0.753+0.020

- 786+
- 829+
«735+
- 788+
. 730+
621+
. 666+
. 767+

.014
.012
-009
-010
.017
.018
-021
.027

070+0.026

+0.

eta]

eal

-048 =
-151+
-026
-142+
107+
- 230+
-191+

-021
-017
-016
-033
-041
-041
-049

1From Fs of the inbred speck line described later.

Table 16 and figure 9 show the result.

The break after I's represents
the same treatment as that given to the 1002 line (p. 10)—4. e., two
generations of unselected mass cultures.

This line gives perhaps the clearest evidence of the effectiveness of
selection that we have yet observed. Reversed selection begun in
F, was apparently also successful.

consistently lower means than any other here recorded.

Finally, the line after F. gives

AN ANALYSIS OF THE EFFECT OF SELECTION.

Fig. 9.—Means and standard deviations for speck (1331) minus line.

TaBLe 16.—1331 (Speck), Minus Line.

Genera-
tion.

He He He

.187+

CO 0 He He RWW RE eR

M

464+0.044
688+ .031
026
141+ .017
072+ .016
982+ .022
943+ .019
333+ .071

000+0.076
417+ .072
081+ .045
951+ .031
188+ .167

REVERSED SELECTION.

-429=0.035
-451 .052
- 143+

.114

0.733+0.031
-790+= .022
767 .018
495+ .012
-425+ .012
414+ .015
341+ .013
.547= .050

0.535+0.048
-638 .051
-629+ .031
-584 .028
-948+= .118

-170 .028

0.663+0.025
-743 .037
-773 .080

1Jncludes data from reversed selection.
*Includes culture 2625, a mating of 6X6. This culture is not included in the other columns.

19

20 AN ANALYSIS OF THE EFFECT OF SELECTION.

GENERAL RESULTS OF SELECTION EXPERIMENTS.

In every case the selected lines showed means that differed from the
mean of unselected Dichets in the direction in which selection had
been carried on. Owing to the apparently large environmental influ-
ence on bristle number, it is in most cases difficult to be sure how this
result was brought about, or, rather, at what stage in the process.

In the case of the 1331 (speck) minus line, however, the change seems
to have been effected fairly rapidly at first, and slowly, if at all, later
on. In the case of the 1002 line there was probably no effect in the
later generations. Reversed selection was uniformly successful if
begun in the early generations, but not usually so at later stages.
These are the results that would be expected on the view that modify-
ing genes are involved.

It is to be observed in the case of the plus lines that the means vary
inversely as the standard deviations—that is, that the two curves
are much like mirror images. In the minus lines the two quantities
usually vary together, giving curves that are nearly parallel. These
relations hold surprisingly closely for many of the curves, especially
those of the plus lines. They are due to the fact that a change in the
mean is almost always brought about by an elimination or great de-
crease in the number of individuals at one extreme of the population
rather than by a marked change in the position of the mode or of the
other extreme. This is strongly in favor of the view that selection
has been effective in eliminating ‘‘unfavorable’”’ combinations rather
than in producing entirely new types.

The relation between the crossbred and inbred series is too much
obscured to repay detailed analysis. Evidently such experiments
with this character would have to be carried out under carefully con-
trolled environmental conditions before they could have any great
significance.

CROSS OF TWO INBRED PLUS LINES.

Since the two inbred plus lines, 864 and 1002, came from slightly
different sources (see above), and were kept separate while being plus
selected, it seemed possible that different plus modifiers had been
isolated in the two lines. If this were the case, crossing them should
result in increasing the variability in F,, and the parent-offspring
correlation when the F, individuals were bred to produce F3. The
F, population should contain genetically unlike individuals, and
should yield to selection in either direction. As a matter of fact, no
such result was obtained.

Table 17 gives the result of the experiment. The 1941 set is per-
haps the clearest case, so we may consider it alone. The parents of
1941 came from 1763 (Fi) of the 864 line) and 1788 (F; of the 1002
line). As table 17 and figure 10 show, the standard deviation in F2

AN ANALYSIS OF THE EFFECT OF SELECTION.

TasBie 17.—Inbred Plus Lines Crossed.

Generation. n M o ip

1 Vere eee ea 192 | 5.365+0.041 | 0.824+0.029 |.................

ges. siskees are 689 | 5.374 .022 mea dae rc OLD lla rcraye severe cla cleretterar ots

1941 Ser ALONE.

isieyevstrajeher arate 42 | 5.500+0.080 | 0.764+0.056

Wate watetasiete se 279 | 5.233+ .034 .843+ .024 | 1—0.278+0.044
Total 605 | 5.783+ .018 .666+ .013 — .0386+ .027

F; 4 Plus 395 | 5.767+ .023 AAS ME OIG) Eiger ene OSCR
Minus 210 | 5.814 .031 GLO Sar OZZMIN cits: crave cocie tee ale ot te
Total 303 | 6.116+ .020 .5383+ .014 + .131+ .038

Fy 4 Plus 270 | 6.144+ .022 POLO == NOLS. cinvsncrsvaycis) tessa skevere is
Minus 33 | 5.879+ .069 {D887 OF0N le neta noaieee ore

1,789
es

1 Does not include culture 2054, in which the mother was not-Dichet.

11

i }

Fic. 10.—Means and standard deviations for cross of two inbred plus lines.
Fic. 11.—Means and standard deviations for cross of 1002 inbred plus
and speck (1331) minus lines.

21

was nearly the same as that in F,, the F,-F; and F;—F, parent-offspring
correlations were not significantly different from 0, and the means of
the plus and minus selected series in F; and F; were practically identi-
eal. This constitutes practically a proof that the two lines did not

differ with respect to modifying genes.
is by no means highly improbable on the multiple-factor view.

The result, while surprising,
The

22 AN ANALYSIS OF THE EFFECT OF SELECTION.

two lines both came in large part from the sepia, spineless, kidney,
sooty, rough, and peach, spineless, kidney, sooty, rough stocks, and
therefore selection presumably had similar material to work with in
both cases. That the result was the same is, then, only a somewhat
unexpected coincidence. It may be pointed out that the identity of
the two lines is borne out by their very similar behavior after the
seventh and tenth generations, respectively. (See figs. 3 and 4, above.)

CROSS OF PLUS AND MINUS LINE.

When two races that differ in quantitative characters are crossed,
the usual result is an increased variability in F, and an increased
F.-F; parent-offspring correlation. This result was obtained in the
present case, as is shown by table 18 and figures 11 and 12, which
give the data for a cross of the 1002 plus and 1331 minus lines.

TaBLE 18.—Cross of Inbred Plus and Inbred Minus Lines.

Generation. n M o r

iBteptoeaes 53 | 5.679+0.049 | 0.542+0.035

ID Sicold caso 369 | 4.694 .037 | 1.052 .026 | +0.193+0.034

Bgicgsvaysatevsts 1,133 | 5.524 .016 .787+ .011 | + .258+ .019

Dy eegperes sess <1 1,078 | 5.492 .013 -610+ .009 | + .330+ .019
1,555

1Calculated after elimination of aberrant culture 3077.

Such a result is capable of explanation in either of two ways. It
may be due to the segregation of modifying factors, or it may be due
to contamination of unlike allelomorphs in the F, individuals.

The contamination hypothesis presents some unusual features in
the present case; for the F, Dichzts were not heterozygous for one
plus Dichet gene and one minus one; homozygous Dichets always die.
Half of them had one plus selected Dichzt gene and one minus selected
normal allelomorph of Dichet (7. e., not-Dichet), the other half had
one minus selected Dichzt and one plus selected not-Dichet. Both
not-Dichets, when homozygous, give for the most part 8-bristled
flies, which are more “‘plus” than any Dichet race. Nevertheless,
on the contamination view, each must contaminate its mate in the F,
fly, in the direction in which it has been selected. Even the minus
selected not-Dichet, that makes for 8 bristles, must contaminate the
plus selected Dichzt, that makes for 6 bristles, in such a way that
the resulting Dichzt gene makes for only 4 or 5 bristles. That is,
‘‘plusness”’ or ‘‘minusness”’ and ‘‘Dichetness’’ must be separable,
and a degree of ‘‘minusness” that affects the result produced by a
not-Dichet gene only very slightly must nevertheless be capable of

AN ANALYSIS OF THE EFFECT OF SELECTION. 23
transference to a Dichet gene and must materially affect the result
produced by that Dichet gene.

The hypothesis that modifying genes are responsible for the result
meets with no such complications.

LOCATION OF MODIFYING GENES.

The selection experiments recorded
above have demonstrated that Dichet
lines exist that are genetically different z
with respect to bristle number. The “
cross between the 1002 plus line and
1331 minus line showed that there is an 20
increase in variability in F, when two
such lines are crossed. Both these facts
are consistent with the view that modi-
fying genes, other than the Dichet gene
itself, have influenced the bristle num-
ber of Dichzt flies. But it would also ,,
be possible to interpret the result as
due to variations in the Dichet gene it-
self, and to contamination of that gene *
in crosses. (See above.)

It has been pointed out by Muller and
Altenburg (Morgan, Sturtevant, Muller
and Bridges, 1915, p. 191), by Dexter 4
(1914), and by Muller (1917) that there
is a method of distinguishing between 20
these two possibilities. The truncate
race of Drosophila with which Muller
and Altenburg worked is characterized
by shortened ‘“‘truncated”’ wings. The
race does not breed true for the trun-
cate character, but the percentage of

80

L523 see oC eins)

Fig. 12.—Results of crossing 1002 in-
bred plus and speck (1331) minus
lines. The P; curves represent the
last few generations of each parent
race. All four curves are reduced to

truneates produced and the degree of
truncation shown are both capable of

the percentage basis; the ordinates
represent percentages and the ab-
scisse bristle numbers.

modification by selection. Muller and
Altenburg showed that this race contains a mutant gene in the second
chromosome that is primarily responsible for the truncate character.
By means of linkage experiments involving readily classifiable mutant
characters they were able also to show that there are modifying factors
for the truncate character in the first and in the third chromosomes.
Furthermore, when the stock was by special methods kept uniform in
constitution with respect to the truncate gene itself and with respect to
these modifiers, selection was without effect. In this way the genetic
variability of the race was shown to be due to modifying factors.

24 AN ANALYSIS OF THE EFFECT OF SELECTION.

Dexter (1914) showed by similar methods that the chief gene for
the variable character beaded is in the third chromosome, and that
there is a modifier in the second chromosome. These results have
been verified by Muller (1917).

In making such tests for modifying factors it is very desirable that
the test stocks, as well as the selected stocks that are to be tested,
should be homogeneous for modifying genes. This is desirable in
order that the tests may be repeated, and in order that results ob-
tained with different stocks may be compared. It was for this pur-
pose that the speck minus, or 1331, line of this paper was obtained.
(See above for history of this line.) This line, in the later generations,
was homozygous for the recessive mutants speck (chromosome II)
and sepia and rough (chromosome III). Since it had been inbred
and minus selected for several generations, it was probably uniform
in constitution with respect to modifiers. Since the other selected
lines also became homozygous for rough in later generations, it was
desirable to have a uniform not-rough line. For this purpose a pair
was taken from the speck stock, wild type in other characters. From
this pair a line was established, and continued by strict brother-sister
pair matings, in order to obtain a stock nearly or quite homozygous
for all its genes. This material is designated ‘“‘speck stock.” All
individuals from it that were used for test. purposes came from 8 or
more successive brother-sister matings.’

Sex-linked modifiers would become apparent in F, when two races
were crossed, since the males from reciprocal crosses would differ and
each type would resemble the maternal race. There is no clear evi-
dence of the existence of such modifiers in this experiment, so the sex
chromosome will be ignored in the discussion that follows.

The method used for detecting second-chromosome modifiers is
as follows: Two lines are crossed, one of which contains speck, the
other not; one or both have Dichet (fig. 13). The F, Dichets are
then heterozygous for speck, and for any second-chromosome
modifiers in which the two lines were different. If an F, male is now
mated to a speck not-Dichet female, there will be no crossing over
between speck and the modifiers. Therefore the not-speck Dichets
produced will receive second chromosomes from their father which
will be identical with those present in the P; not-speck race (in the
diagram the Dichet race), while the speck-Dichet back-cross
individuals will receive the second chromosome that came from the
other P; race. Since the two types are alike in their third chromosome
constitution, and since they have been reared in the same culture bot-
tles, so that environmental influences were the same, any differences

1 With the exception of culture 1737 (see Appendix), all were from 10 or more successive brother-
sister matings. All these specks were from the same Fs pair. All those before culture 2430 were
from the same Fs pair. All those after 2430 were from a different I's pair, but were themselves
from the same Fy7 pair. F1s5 and Fis were mass cultures instead of pairs.

AN ANALYSIS OF THE EFFECT OF SELECTION. 25

between them must be due to second-chromosome differences between
the two P, races. This experiment may be continued further by
mating the not-speck Dichzet males produced by the back-cross to the
speck not-Dichet females. Such a mating should give the same result

I ait I aug
see OE iets chee oe
R pistig, <2
a
0 stg I ate
DT se Pa oe. Spe Beene e
Pde a= sera Test 9 ok RE ee
Sp Sp
I ali I si
D’ staswSp dD
PRC eS IN aN My gt ss sa
Sp Sp
Fie. 13.

as the first back-cross and does in fact do so. In table 19 both types of
experiment are treated together. Figure 14 is a graphical representa-
tion of the result of one experiment of the type here described.

It should be noted that such experiments are suited only for the
detection of dominant modifiers present in one P; race, or, stated
conversely, recessives present both in one P, race and in the speck race
from which the test female came.

TaBLE 19.—" Tests, Chromosome IT.

Source. Means. Distributions.
Tested
Not-sp. sp. againsy— Not-sp. sp. Diff. Diff. x? P
P. E.

804. tis ssacios sp. stock | sp. stock |5.314+0.045/4.462+0.050| +0.852+0.067| 12.7 |69.4 0.000000 +|
1002). .iaeBiners 212 sp. stock | sp. stock |5.924+ .026/5.732+ .031/+ .192+ .040) 4.8 |13.3 | .004
BOOZ ao. 70s ove eyes sp. stock 1331 5.824 .062/5.385+ .117/4+ .489+ .132) 3.3 | 4.77) .10
4002 2 3 esicoee. 43 1331 1331 4.983 .063/4.438+ .065)+ .545+ .091} 6.0 /17.7 | .001
1002). cyte 1331 sp. stock |6.095+ .043/5.750+ .104/+4+ .345+ .113) 3.1 | 6.17] .05
Cross-br. plus. .| sp. stock | sp. stock |5.412+ .063/4.686+ .097/+ .726+ .116) 6.3 /19.0 | .0003
900s. case sp. stock | sp. stock |4.711+ .062/4.442+ .070/+ .268+ .093) 2.9 | 3.95) .27
Cross-br. minus.| sp. stock | sp. stock |5.304+ .087|4.762+ .101/+ .542+ .133/ 4.1 | 6.67] .04
Cross-br. minus.| sp. stock 1331 4.353 .067/4.151+ .045/+ .202= .081] 2.5 | 5.59) .24

Table 19 gives the results of the experiments of this type that have
been carried out. (For the raw data see Appendix.) The first two
columns give the P; races, or in cases where the tested male came
himself from a back-cross test, the original source of his not-speck
and speck chromosomes. The third column gives the source of the
test female. All tests in which the data for these three columns were
identical have been lumped. The next three columns give the mean

26 AN ANALYSIS OF THE EFFECT OF SELECTION.

bristle number of the two classes of Dichzt offspring and the differ-
ence between these two means. ‘The sign of the difference is given as
positive when the not-specks had a higher mean than the specks (as
in all these cases); negative, as in other results (see below), when
the specks were higher. In the col-
umn headed oe. is given the quotient
of the difference between the two means
divided by its own probable error, a
measure of the probable significance of
that difference. The last two columns
give the x? and P values for the two
(speck and not speck) distributions,
considered as wholes.

These data make it certain that the
864 plus line and crossbred plus line
both contained second chromosomes
with one or more plus modifiers domi-
nant to minus modifiers in the second
chromosome of the speck stock. The
1002 plus line had similar modifiers,
and also had the same relation to the
1331 minus line. It is probable, from
the results obtained with the 1002 line,
that the speck stock and the 1331 line
had some minus modifiers in common, Ay oR
but that the second chromosome of the ee Fee vio) aoe ee
1331 “line -was-more~ strongly-minus. —... "ale bere ee one
Both these latter results would have based on 153 not speck and 106 speck
been expected, since the second chro- _ Mies, are both reduced to the percent-

® 3 age basis. See table 19 for statistical
mosome of the 1331 line came, in part treatment.
at least, from that of the speck stock,
but has been minus selected, while the speck stock has not been
selected at all for bristle number.

The experiments just discussed show that the second chromosome
contains one or more modifiers, but give us no information regarding
the loci of such modifiers. It is possible, on the basis of this data
alone, that speck itself is the minus modifier. If, however, a heterozy-
gous female is tested by mating to a speck not-Dichxt male, there
will be a possibility of crossing over between speck and any modifiers
in the second chromosome. The result would be that the speck and
not-speck offspring differ less than when an F, male is tested. There
is, of course, also an opportunity for crossing over in the third chromo-
somes of such females, so that the Dichet offspring will not be all
alike with respect to their third chromosomes, as they were when the
male was tested; but the same crossover classes should occur among

AN ANALYSIS OF THE EFFECT OF SELECTION. 27

both the speck and the not-speck offspring, and in identical propor-
tions. Therefore this factor should not influence the end-result.

Table 20 shows the results obtained from such experiments. The
arrangement is the same as in table 19.

As was expected, the differences here are less than in the correspond-
ing tests, but are still present and in the same direction when significant.
This result proves that one or more of the second-chromosome modi-
fiers cross over from speck in the female.

TasBLEe 20.—2 Tests, Chromosome IT.

Source. Means. Distributions.
Tested |—
against— Diff.
Not-sp. sp. Not-sp. sp. Diff. PE. x? Pp
GS ralcce ster taiats sp. stock 1331 4.971+0.097|4.600+0.082|+0.371+0.127| 2.9 | 4.59 0.21
SBS a isvciefeccue sexe 1331 sp. stock |4.674+ .059/4.321+ .067/+ .353 .089) 4.0 9.10 .06
SEF Waveraataialateste 1331 1331 4.448+ .043/4.245+ .044/+ .203+ .062| 3.3 |13.1 .004
QO 2 Kiaterateheverersts sp. stock | sp. stock |5.543+ .074/5.3934 .104/+ .150+ .128) 1.2 2.78 -43
ROOD ier rcrtctercreis sp. stock 1331 4.875+ .062/4.787+ .070/+ .088+ .093) 0.9 | 1.39 .92
TOOZMe ci. :tsy7- ic 1331 1331 4.617+ .046/4.250+ .056/+ .367+ .073) 5.0 |13.8 .03
LOO He eysitebyaree 1331 sp. stock |5.336+ .027/5.390+ .048]/— .054 .055) 1.0 | 8.93 .26
Cross-br. minus.| sp. stock 1331 5.259 .097/4.727+ .152/+ .532+ .180} 3.0 | 7.97 .05
Cross-br. minus.| sp. stock | sp. stock |4.350+ .086|4.609+ .090)— .259+ .125) 2.1 | 2.21 84

THIRD-CHROMOSOME MODIFIER.

If we cross two races, one of which is Dichet rough, the other wild-
type, the F, female will have the constitution D’r,. If such a female
be mated to a not-Dichet rough male, there will be two types of
Dichzet offspring—the non-crossovers will be rough, the crossovers
not rough.! If the two original chromosomes differed in modifying
factors somewhere near rough, these two types of offspring will differ
in their bristle number.

Such tests have been carried out, with the results shown in table
21.2. In only one case (the third) was a significant difference obtained ;
but that case proves that there was a dominant plus modifier in the
1002 line, located somewhere near rough, or a dominant minus modifier
in the speck stock, but not in the 1331 line and in the same region.
Since the 1331 line was derived from a cross involving the speck stock,
and had been minus selected ever since that cross, it is probable that
dominant minus modifiers present in the speck stock would have been
preserved in the 1331 line. It is, therefore, almost certain that the

1 There will be some doubie crossovers, but these will be rare. There will, be course, also be

two classes of not-Dichets.
2 In the case recorded in the second row, the Dichet and rough came from different parents,
so that the non-crossover and crossover classes are reversed. The experiment is the same in

principle as that outlined above.

28 AN ANALYSIS OF THE EFFECT OF SELECTION.

1002 line contained a dominant plus modifier in the region of the
rough locus.?

There can be no question that the lines studied do differ in their
constitution with respect to definite modifying genes that affect
bristle number. In the case of the 1002 and 1331 lines there is at
least one modifier, and probably two, located in different chromosomes.
This gives the explanation of the increased variability observed in F,
when these lines were crossed. The only other available explanation of
that phenomenon—contamination of allelomorphs—has already been
shown above to lead to complications in this case. (See also below.)
Since it is both improbable and unnecessary, it may safely be dis-
carded.

TABLE 21.—9 Tests, Chromosome III.

Source. Means. Distributions.
Tested —
against— Diff.
Not-ro. ro. Not-ro. ro. Diff. PE. x?

Sp. stock. 864 1331 |4.793+0.106/4.761+0.081| —0.032+0.133] 0.2 | 1.76] 0.60

Pantie 1331 1331 |4.750+ .071/4.581+ .091)/+ .169+ .115) 1.5 | 1.09 .58
Sp. stock. 1002 1331 |4.697+= .065|5.098+ .042)/+ .401+ .077| 5.2 |18.7 . 002
Sp. stock.| cross-br. minus 1331 |4.323= .089/4.2764 .092)/— .047+ .127| 0.4 | 0.33 .999

THIRD-CHROMOSOME LETHALS.

Culture 1264, belonging to the third generation of the 1002 inbred
plus line, produced, in the last 6 days it was counted, 60 Dichets and
no not-Dichets. It seemed possible that one of the parents was
homozygous for Dichet, so the line was continued. It was finally
bred through about 18 generations, and produced 2,735 Dichets and
only 4 not-Dichets. The 4 not-Dichets suggest the hypothesis that
all the Dichets are really heterozygous as usual, but that they carry
a lethal in the other chromosome that kills the not-Dichets.? That
they are heterozygous has been shown by out-crossing them. When
mated to Dichets of other strains the result was 211 Dichets to 103
not-Dichets (4 cultures), the 2 : 1 ratio usually obtained when Dichets
are mated together. When mated to not-Dichets the result was 207
Dichets to 209 not-Dichets (6 cultures)—a normal 1:1 ratio. That
there is a lethal in the stock has been shown by mating Dichets of
this strain to Extended flies and inbreeding the not-Dichet offspring,
which were found to carry a lethal as expected. (See below.)

1 The second row of table 18 seems to contradict the conclusion that the 1002 and 1331 lines
differed with respect to a modifier near rough. However, the experiment represents only a few
flies, and did not give a significant result. Moreover, it was carried out before the 1002 line
had been very long inbred (F's), and involved a not-rough chromosome from that line, which had
not then become homozygous for rough.

2 See Muller (1917) for a discussion of autosomal lethals.

AN ANALYSIS OF THE EFFECT OF SELECTION. 29

The 4 not-Dichet flies produced by uncrossed descendants of 1264
appeared in cultures 1516, 2424, 2571, and 2851. Since most of the
flies of this line are heterozygous for other factors in chromosome III,
it should be possible by an examination of these 4 flies to determine on
which side of Dichzt the lethal lies; for these flies are evidently cross-
overs between Dichet and the lethal, and should show certain rela-
tions with the other characters, depending on the locus of the factor.

The 4 cultures in question gave the results shown in table 22 (both
parents in 1264 being rough, all these flies are rough).

TABLE 22.
Dp D’ ss so. | D’ so. not-D’. not-D’ ss. | not-D’ so.
1516 | 106 6 4 1 0 0
2424 | 78 Dichets, some ss. 0 | 1 ‘
2571 | 49 Dichets, with some D’ pe ss so. 0 0 1

2851 | 41 Dichets, 1 not D’; other characters not noted.

Since the other characters were not noted in 2851, that bottle is
useless for our present purposes. The constitution of the parents in
the other three cultures must have been as follows:

1516: Bakes Z
Iy118s e8 Iy118s e8
, /
2424: Lee Date
linss li118s
1D D’
OG lp? ss ef Ip? ss e&

Since there can be no crossing over in the male, there must in each
case have been a crossover between D’ and l,,, in the female. 1516
indicates that l,,, is to the right of D’; 2424, to the left if the individual
was a single crossover. But the distance D’ s,, here involved, is
known to be long enough so that double crossovers sometimes occur
in it. In 2571 the distance involved is D’ p’, which is too short for
a double crossover, therefore /,,, is to the right of D’. The position
of l,,, being thus obtained, the not-D’ produced by 2424 must have
been a double crossover.

The next problem is: How far from Dichet is the lethal locus?
The mating is always—

Dies
li lin

There being no crossing over in the male, the sperm are of two
kinds only—D’ and l,,. The non-crossover eggs are of the same

30 AN ANALYSIS OF THE EFFECT OF SELECTION.

constitution, but there are also the crossover eggs, D’ l,,,, and +.
If we let the non-crossovers be to the crossovers as x: y, the result of
the mating will be:

p= dies. a di
Leary ie
; am y an
Il py PU a HY
D’ =p)’. D D
font _ dies ate =not-D’
lin l

The result then is:

2a+y=D' y =not-D’
100y _ 200 (not-D’)
x+y D’+not-D’

Per cent crossovers =

In the present case this formula gives the crossover percentage
as 0.29. Lethal III is, then, located 0.29 to the right of Dichet.

Another lethal of the same sort as the one just described appeared
in culture 1546. This culture belonged to the sixth generation of the
same line in which the first lethal was found, and was descended from
a sister pair (1213) to 1264, the first culture in which that lethal ap-
peared. Since the two lethals are certainly distinct, as will appear
below, this relationship is to be regarded only as a coincidence. Three
cultures of this strain were made—1546 and two daughter pairs.
The result was 154 Dichets and 1 not-Dichet. The 1 not-Dichet
was from culture 1681. The Dichets from this culture show both
parents to have had the constitution

ID?
sell s.esr,

The not-Dichzt individual was spineless, sooty, rough. This indi-
cates that the lethal was to the left of Dichet; otherwise the egg in
question must have resulted from a sepia Dichset spineless triple cross-
over, which is a very rare occurrence. By the method outlined above
it may be calculated that the lethal gives 1.29 per cent of crossovers
with Dichet.

That these two lethals are distinct is indicated by the following
culture, 1915. The female of this mating came from culture 1791,
which gave 31 Dichets and no not-Dichets. 1791 was an F, from a
cross involving 1419 of the 1264 line, and thus its lethal must be sup-
posed to be that of 1264. The male of the test bottle 1915 was from
1681 of the second lethal strain. Therefore, if the two lethals are the
same, 1915 should have given few or no not-Dichets; if they are dif-
ferent it should have given 2 Dichets to 1 not-Dichet. The actual

AN ANALYSIS OF THE EFFECT OF SELECTION. 31

result was 51 Dichets to 30 not-Dichets. Evidently, then, the two
lethals are distinct, as was previously indicated by the fact that they
are probably on different sides of Dichet.

It seemed possible at first that one or both of these lethals might
be due to a breaking up of the Dichset factor, whereby its lethal effect
had been separated from the effect it produces on the soma of a het-
erozygous fly. This hypothesis is negatived by two considerations:
(1) both lethals have been shown to occupy loci different from that
for Dichxt; (2) the lethal effect of Dichet is not allelomorphic to that
of these factors, since a fly with Dichet in one chromosome and either
of the lethals in its mate does not die.

EXTENDED.

In culture 1379, of the crossbred plus series, there appeared several
flies intermediate in appearance between Dichet and the normal.
These flies had the bristles of the normal flies (including the anterior
post-alars, always reduced or absent in Dichets), but had their
wings spread out to a greater or less extent. These individuals were
tested, and were found to have a dominant factor, responsible for the
extended wing character. The character has been called “Extended”
(see plate 1, fig. 1). It occasionally overlaps the normal, and is there-
fore not favorable for linkage experiments. It is, however, sufficiently
uniform in appearance to make it possible to work out its inheritance
with certainty. The gene is found to be an allelomorph of Dichet,
and is designated D®. Like Dichet, it is lethal when homozygous;
and the flies with Dichet in one chromosome and Extended in the
other also die. These conclusions are based on the following results:

Preliminary experiments involving speck (chromosome IT) and
various characters in chromosome III showed that Extended crosses
over freely from speck in the male, but gives apparently no crossing
over in the male with sepia, spineless, or rough. These data are not
very satisfactory, owing to the fact that some of the Extended flies
are very similar in appearance to the not-Extended, and there is too
great an opportunity for being influenced by the other characters of
the flies when making the separation. However, no crossovers were
discovered among 308 flies.

When tests were made of heterozygous females, there was found
to be a slight excess of not-Extended offspring, presumably due to
incorrect classification. The proportion of crossovers, based on Ex-

‘ 13 ;
tended offspring only, was i057 12.4 per cent for sepia Extended

Val
and jaa "8 per cent for Extended spineless. In one experiment in

which all three of these factors were observed at once, the result shown
in table 23 was obtained.

a2 AN ANALYSIS OF THE EFFECT OF SELECTION.

It is evident from these data that Extended is between sepia and
spineless, some distance from either. It is, then, in the same general
region as Dichet.

The lethal effect of Extended has been tested in two ways. Mat-
ings of Extended by Extended gave 116 Extended to 94 normals.
If homozygous Extended is viable the result should be 3 : 1; if it
dies the result should be 2:1. In fact, it was nearer 1:1. This
result is probably due to the overlapping phenomenon, resulting in the
classification of some Extended flies as normal. It is suggestive of a
2:1 ratio, however. More conclusive data was obtained by mating
heterozygous Extended to Dichet flies heterozygous for lethal III
(see above), and inbreeding the Extended offspring. If Extended is
lethal when homozygous, these flies should produce only Extended
offspring, but these should all be heterozygous. They should, in fact,
breed exactly like the true-breeding race of Dichets described above.
This is actually the case. Such a stock has now been kept for four
months, and is still made up almost entirely of evidently Extended flies;
but tests show them to be only heterozygous for the character.

TABLE 23.
Dé
ee XS,8s
De | Sasa Ss 8, Dé | Des; Be N | se D* ss | Total.
39 37 3 3 6 10 0 1 99

The mating of Dichet X Extended (or vice versa) gave the following
result: Dichet, 99; Extended, 69; normal, 102; total, 270. If we
suppose some of the flies classified as ‘‘normal’’ to be in reality Ex-
tended, this result approximates to the 1:1:1 expected if Dichet-
Extended flies die. The fact that the Dichets are only about a third
of the total shows that half the Dichet gametes have been eliminated
somehow. One of the Dichzets and a number (4 individual matings
and 2 mass cultures) of the Extendeds have been tested, and neither
sort has produced the other. It is, then, safe to conclude that Dichet-
Extended flies die.

Culture 1379, in which Extended first appeared, was made up by
mating together two 8-bristled flies, the male from 1145, the female
from 1253. The latter culture gave among other offspring 5 sevens
and 2 eights. The other eight, in 1356, behaved normally, as did
one of the sevens (in 1357). Culture 1145, however, gave no seven
and only the single eight. Since 1379 gave a result indicating that one
parent was Extended instead of 8-bristled Dichet, it seems probabie
that the male parent, from 1145, was the mutant. In either case,
the Extended parent was produced by mating a 7-bristled Dichet

AN ANALYSIS OF THE EFFECT OF SELECTION. oa

female to a 6-bristled Dichet male, both parents being from the cross-
bred plus selection series.

It follows from the data presented above that Extended is an allelo-
morph of Dichet intermediate between Dichet and its normal allelo-
morph in its somatic effect, and that it arose in a fly heterozygous for
these two factors. It is, then, the kind of thing one would expect
contamination of allelomorphs to produce. On the other hand, it
seems at least equally possible to suppose that it arose as a mutation
of one or the other allelomorph, without the presence of the other or
the one having had any influence on the event. In any case, the
process must be an extremely rare one, for it has been detected only
once, in spite of the very large number of offspring of heterozygous
Dichet flies that have been observed and bred.

Since the Extended flies have more bristles than Dichets, it may be
supposed that the fact that the former arose in a plus-selected series
is significant. Such a supposition has actually been made by Castle
(Castle and Phillips, 1914, ete.) with regard to a similar case in hooded
rats. As has been pointed out by MacDowell (1916), a mutation in
the direction in which selection is being made has a very much better
chance of being discovered than has one in the opposite direction.
Moreover, these mutations have been demonstrated only in an ex-
tremely small number of cases; and a very elementary knowledge of
the theory of probability will suffice to convince one that a considerable
number of cases must be established before one can conclude that muta-
tions are more likely to occur in one direction than in another. No
argument based on one or two cases, however well established those
cases may be, can carry any conviction.

“DICHATE INTERMEDIATE.”

The Star Dichet stock in the Columbia laboratory was found to
have in it some flies that were indistinguishable from Extended. It
seemed possible that these flies were due to an independent occurrence
of the Extended mutation. Since the Star Dichet stock is kept by
mating (Star) Dichet flies together in each generation, the mutation
responsible for these ‘‘intermediates’’ must either have occurred in a
Dichzt fly (as did the Extended mutation), or have been in the stock
since it was made up. The fact that Dichets are mated together in
continuing the stock seemed, however, to show that the character
was not true Extended, since, as we have seen above, Dichzet-Extended
flies always die. But the possibility remained that “intermediate” was
another non-lethal allelomorph of Dichet. Accordingly, tests were
made as follows:

Matings of Dichet by Dichet gave some intermediates, showing
that the continuance of the character in the stock was not dependent
on the use of non-virgin females, and proving that the character was
not Extended.

34 AN ANALYSIS OF THE EFFECT OF SELECTION.

Matings of intermediates by intermediates gave both intermediates
and normals, showing that the character was either dominant or irreg-
ular in appearance.

Matings of intermediate to specks and to black purples of other
stocks gave only normals, showing the character to be recessive.

Mating together the F, normals from the last type of matings gave
a few intermediates; but these were in no case speck or black or purple.
This is the usual behavior of a second-chromosome recessive, due to
no crossing over in the F; male. Hence ‘‘intermediate”’ is a recessive
character, and lying in the second chromosome. Its occurrence in
the Star Dichzet must have been only a coincidence, and can have had
nothing to do with the presence of Dichst in that stock. The differ-
ence between this character and Extended is a striking illustration
of the danger of arguments as to the identity of characters based on
similarity of appearance.

NOT-DICHATS FROM SELECTED LINES.

As has already been pointed out, Dichet flies almost always have
fewer bristles than have normals. All Dichets are heterozygous for
the normal allelomorph. Therefore, in such an experiment as this
one, in which Dichets are repeatedly mated together, one obtains
normal flies the not-Dichzt genes in which have been associated with
Dichet genes for many generations. The experiment is, then, suited
for a study of the question as to whether or not factors “contaminate”
their allelomorphs. If this contamination occurs, one might expect
the not-Dichet flies to show a tendency to have fewer bristles than
they normally have, and the Dichets to have more. That Dichets
tend to increase in bristle number is very improbable. The stock
has now been kept, always of necessity in heterozygous condition, for
more than 40 generations. There is no evidence that any progressive
change has occurred, though no selection has been used in keeping
the stock cultures. The modal class at present (5 bristles) is actually
lower than the class (6) of the original mutant.?

There are some data regarding the bristles of the not-Dichets pro-
duced by selected Dichets. Counts of these bristles have been taken
only occasionally (see table 24), but whenever a bristle number other
than 8 has been observed in such flies it has been noted on the record
sheet. Examination of these notes shows that in the minus-selected
series there are several records of 6 and 7 bristled not-Dichets, but
none of numbers higher than 8. In the plus selected lines there are a
number of records of nines and tens, but no sixes and only 1 seven
(from 1190, an Fs of the crossbred plus series). The complete counts
taken of bristle numbers are given in table 24.

1It may be pointed out that the familiar yellow mouse and several similar cases in Drosophila
afford evidence of the same sort against contamination.

AN ANALYSIS OF THE EFFECT OF SELECTION. 35

There is no evidence for contamination. With the one exception
noted above, all the variations are in the direction for which the
Dichets were being selected. On the multiple-factor view one would
expect this result, since it would seem likely that any modifier would
usually affect Dichets and not-Dichets in the same direction. The
one exception, a 7 from 1190 of the crossbred plus series, is scarcely
surprising on this hypothesis, in view of the facts that unselected not-
Dichet races may produce sevens (see table 2), and that 1190 was prob-
ably not homozygous for a large number of plus modifiers. Since
this individual was not tested, it would perhaps be futile to argue the
ease further.

TABLE 24.
Bristle Nos.
Culture. Series. Genera-
tion
6 7 8 9 | 10
1277 SOA pHs se swe. 7 57
1285 Crossbred plus. ... . a 35 i!
1357 Crossbred plus. .... 8 et) Pome frees 4
1810 S64epluge. Sie oes was 10 ae ay [ood
1811 1O02 plus ysc.< ttt 7 16
1268 Crossbred minus... . 6 seul vito ale
1273 Crossbred minus... . uf anal lice ee:
1878 Crossbred minus... . 10 on, Ih eee ALD:
1879 Crossbred minus... . 10 SEL Ga | caw)
1881 Crossbred minus... . 10 sere [teetee eae,
1882 Crossbred minus... . 10 on 1} 31
1892 Crossbred minus... . 10 LPN sats, Pk O
1986 1331 (speck) minus. 5 Ai 8| | onl (4
1996 1331 (speck) minus. 5 A ese nek
2015 Crossbred minus... . 1l Set ida || tote)
ae | ee

It may be noted here that in the Star Dichzt stock referred to above
(p. 31) there were found to be numerous not-Dichets with 9 and 10
bristles. Unfortunately, no counts were made on these flies, and the
nature of the extra bristles was not determined. The stock has since
been ‘‘purified,” to rid it of certain other mutations, and the extra-
bristled flies, formerly plentiful, have now disappeared. This stock,
as stated above, was continued by mating together (Star) Dichet
flies, without regard to bristle number. These extra-bristled not-
Dichets therefore furnish evidence of the same type as that just dis-
cussed, except that the race was not selected for bristle number.

36 AN ANALYSIS OF THE EFFECT OF SELECTION.

GENERAL DISCUSSION.
THE SELECTION PROBLEM: QUESTIONS AT ISSUE.

It appears to the writer that the three questions below are the chief
ones at issue in the discussion of the selection problem:
1. Does selection use germinal differences already present, or differences
that arise during the experiment, or both?
2. In case it uses new differences, does it cause them to occur more
frequently, and does it influence their direction?
3. Are differences, already present or arising de novo, more likely to
occur in the locus of the gene under observation, or in other loci?

It is not, I think, questioned by any one that selection may effect
either gradual or sudden change in the mean character of mixed races,
or that it may even, occasionally, produce such an effect in pure races
if a mutation in the desired direction happens to occur.

1. Does selection use germinal differences that are already present, or differences
that arise during the experiment ?

Everyone who has bred animals or plants is familiar with the fact
that different strains, even when rather closely related, differ in all
sorts of minor points—size, proportions of organs, shade of color, resist-
ance to disease, fertility, temperament, rate and habit of growth—
in fact, in almost any respect that one investigates. This can only
mean that such strains differ genetically; and since the kinds of differ-
ences are usually so numerous, they probably usually have many
genetic differences—t. e., they differ in respect to many factors. In
any race not normally self-fertilizing or closely inbred, crosses between
individuals of different constitution must then be frequent. And
such crosses must, on the assumption that the original differences were
Mendelian, lead to the production of a population more or less hetero-
zygous for factors that produce minor effects on all sorts of charac-
ters. The assumption that the differences are Mendelian rests on the
observed facts, (1) that demonstrably Mendelian factors may produce
effects on practically any kind of character studied, and effects of
practically any observable degree; and (2) that non-Mendelian inher-
itance has never been demonstrated, except for a few cases of plastic
characters in plants and cases of infectious diseases.’ Other kinds
of inheritance may exist; but the available data indicate that they must
be extremely rare. Therefore the chances are that any observed
difference between two strains is Mendelian.

If these conclusions be accepted, it follows that any strain not very
closely inbred is likely to be heterozygous for factors influencing many
characters. Selection for these characters will then be effective in
isolating favorable combinations of such ‘‘modifying factors.”

10One may refuse to call these cases of inheritance if he chooses to define that term so as to
exclude them.

AN ANALYSIS OF THE EFFECT OF SELECTION. 37

Mendelian differences are still arising by mutation and may arise
in a selection experiment as well as anywhere else; and those that arise
in such an experiment are as likely to affect the character under ob-
servation as are any Mendelian differences taken at random. It is
therefore probable that selection sometimes makes use of variations
that arise during the course of the experiment, or, rather, that varia-
tions which may be available do arise.

The question is, what is the relative frequency of the two kinds of
available factor differences—those already present and those that arise
de novo? The answer is found by investigation of the data on selection
in inbred lines and in crossbred lines. In closely inbred strains there are
not likely to be many factor differences present when selection is begun,
while in crossbred lines these differences are likely to be numerous.

That selection is usually effective in crossbred lines is a well-known
fact, demonstrated many times with many different organisms. Not
many experiments have been carried out on closely inbred material,
but those of Johannsen (1903), MacDowell (1917), and the present
paper (p. 11) show that selection may be without effect in such lines.
In two of these cases selection was effective until the lines became highly
inbred. But mutations influencing the characters under observation
have been obtained in the selection experiments of Castle and Phillips
(1914), Morgan (Morgan, Sturtevant, Muller, and Bridges, 1915,
p. 205), Lutz (1911), and those reported in this paper (p. 31).

Apparently, then, selection produces its effects chiefly through
isolation of factors already present, but occasionally available muta-
tions do arise during the course of the experiment.

2. Does selection cause mutations, or influence their direction?

The usual selection experiment consists in breeding from individuals
that are extreme in some respect. This extreme character may be
environmental in origin, or it may be caused by germinal differences.
In the first case, no geneticist is likely seriously to maintain that selec-
tion will have any effect whatever. In case the extreme character
is germinal in origin, selection will of course be effective in eliminating
certain genetic types. Moreover, given a combination of genes that
produce the character in a certain degree, we are evidently in a better
position to reach a further stage than if we have the character less well
developed. For how long a tail will be when it gains an inch evidently
depends on how long it was before it gained that inch. But it seems
incomprehensible that selection of individuals of a constitution favor-

1Evidence derived from forms that reproduce asexually is also available in studying this
question, for such reproduction commonly prevents recombination, and therefore gives results
comparable with those obtained from homozygous strains. Some of the evidence obtained from
studies on asexually produced Protozoa (e. g., Calkins and Gregory, 1913; Jennings, 1916; Middle-
ton, 1915) has shown that selection may be very successful in changing such forms. But it is
very doubtful if these animals are comparable with the Metazoa in the method of distribution

of their chromatin. It seems not improbable that in some cases recombination may here be
possible in asexual reproduction.

38 AN ANALYSIS OF THE EFFECT OF SELECTION.

able to the development of a given character can make more likely
the occurrence of factorial variations affecting that character, or
variations affecting it in a given direction. As a matter of fact, there
is no evidence for such a conclusion. The occurrence of mutations is
ordinarily such an extremely rare phenomenon that it would be very
difficult to obtain statistically significant data in the matter. More-
over, when one is selecting for a character, one is examining his animals
or plants for that character with unusual care, so that any mutations
in that character are very likely to be observed and tested, provided
they are in the direction in which selection is being carried out. It
follows from these considerations that extremely careful controls are re-
quired before any data on these questions can have any significance.
8. Are variations more likely to occur in the locus of the gene under observation,
or in other loci?

In Drosophila over 25 different and independent mutant factors affect
the color of the eye. In mice there are 7 or more independent factors
affecting coat-color. According to Little (1915) there are 2 and prob-
ably 3 independently segregating factors that affect spotting in these
animals. There are at least 14 and probably more definite genes (in
different loci) that affect bristle number in Drosophila, not counting
the “‘modifying factors” studied by MacDowell and the writer.

In view of these and many similar facts, it is certain that changes
in a given character may be brought about by changes in many differ-
ent parts of the germ-plasm. If selection of a given mutant race, say
hooded rats or Dichet Drosophila, is likely to cause or to isolate muta-
tions in the gene that differentiates that race from the normal type
(i. e., the hooded factor or the Dichet factor) rather than in any other
factors, it follows that mutant allelomorphs must be more variable
than ‘‘normal’”’ ones. For, by analogy with mice, hooded rats are
homozygous for the normal allelomorphs of several possible factors
affecting spotting; and Dichet flies are certainly homozygous for the
normal allelomorphs of at least 13 mutant factors that affect bristle
number. It may be true that mutant factors are on the average more
variable than their normal allelomorphs; but no evidence to that
effect is at hand; and owing to the great difficulty of statistical treat-
ment of the frequency of mutations alluded to above, such evidence
will be very difficult to obtain.!

In the absence of such evidence, it is more probable that variations
will appear in other factors, since there are many of them to vary,
but commonly only one that is responsible for the difference under
observation. That changes of the one factor itself may occur in selec-
tion experiments, however, has been shown by Castle (Castle and
Wright, 1916) and the writer (p. 31). It does not follow that selection
has caused these variations or that they are more likely to occur than
are variations in other factors.

1Bvidence has been obtained by Emerson (1917), who used unusually favorable material,
that shows clearly that different allelomorphs may at times differ greatly in their mutability.

AN ANALYSIS OF THE EFFECT OF SELECTION. 39

CONTAMINATION OF ALLELOMORPHS.

When two races that differ in quantitative characters are crossed,
it is frequently observed that F, is fairly uniform, and that F, shows
an increase in variability together with the production of forms inter-
mediate between the parent races and often different from the F,.
There are two current methods of accounting for these cases:

(1) The two races are assumed to have differed in a number of
Mendelian factors affecting the character in question. The observed
result is then explained as due to the recombinations of these factors.

(2) The two races are assumed to have differed in only one factor
affecting the character in question, and the new types observed in F,
are supposed to be due to ‘‘contamination” in the F,; hybrid, that is,
allelomorphs present in the heterozygote are supposed to have influ-
enced each other, so that they do not come out unchanged.

The fundamental principle of the first explanation—that more
than one factor may influence the same character—is admitted by
all Mendelians. But many of the adherents of that explanation are
unwilling to admit that “contamination of allelomorphs” has ever
been experimentally demonstrated. Let us then examine the evi-
dence that is brought forward in support of that assumption.

The following quotations are the chief ones bearing on the ques-
tion that I have been able to find in recent literature:

“The currently accepted explanation (of size inheritance), which its
supporters choose to call ‘Mendelian,’ rests upon the idea of gametic purity
in Mendelian crosses. It assumes that Mendelian unit-characters are un-
changeable and unvarying, and that when they seem to vary this is due to a
modifying action of other unit-characters (or factors) . . .. The idea
of unit-character constancy is a pure assumption. In numerous cases unit-
character inconstancy has been clearly shown, as in the plumage and toe
characters of poultry according to the observations of Bateson and Daven-
port, and the coat-characters and toe-characters of guinea-pigs in my own
observations. Unit-character inconstancy is the rule rather than the ex-
ception.” (Castle, 19166, p. 209.)

I have shown in numerous specific cases that when unlike
gametes are brought together in a zygote they mutually influence each other;
they partially blend, so that after separation they are less different than they
were before. The fact remains to be accounted for that partial blending does
occur (1) when polydactyl guinea-pigs are crossed with normals (Castle,
1906); (2) when long-haired guinea-pigs are crossed with short-haired ones
(Castle and Forbes, 1906); and (3) when spotted guinea-pigs or rats are
crossed with those not spotted (MacCurdy and Castle, 1907). Davenport
has furnished numerous instances of the same thing in poultry; indeed, he has
shown that ‘‘imperfection of dominance”’ and of segregation are the rule rather
than the exception in Mendelian crosses in poultry.”’ (Castle, 1916d, p. 253.)

cs . The English unit-character had changed quantitatively in trans-
mission from father to son. This seems to us conclusive evidence against
the idea of unit-character constancy, or ‘gametic purity.’”’ (Castle and
Hadley, 1915.)

: We are often puzzled by the failure of a parental type to reappear
in its completeness after a cross—the merino sheep or the fantail pigeon, for

40 AN ANALYSIS OF THE EFFECT OF SELECTION.

example. These exceptions may still be plausibly ascribed to the inter-
ference of a multitude of factors, a suggestion not easy to disprove; though it
seems to me equally likely that segregation has been in reality imperfect.”
(Bateson, 1914.)

Fractionation is referred to by Bateson in this same paper as prob-
ably due to imperfect segregation. Illustrations are Dutch rabbit
and Picotee and other sweet peas. (See p. 298.)

“Accordingly we seem limited to the conclusion that a slowly blending
gene is involved in the cross between early flowering and late flowering peas,
that the blending after one generation of heterozygosis may be small in
amount, but after three generations it is in the majority of cases practically
complete, so that the commonest ‘constant’ class in the entire hybrid popula-
tion is one strictly intermediate between the modes of the parental varieties.
This interpretation is entirely in harmony with the observed modification
through crossing of many Mendelizing characters, as observed by Daven-
port, Bateson, and many others in poultry, guinea-pigs, swine, and other
animals, as well as in plants.’”’ (Castle, 1916b, p. 215.)

Hayes (1917) states on the basis of his experiments with variegated
maize:

‘3 One might conclude that certain heterozygous combinations

produce germinal instability which exhibits itself either as Imperfect segrega-
tion, gametic contamination, or sporophytic variation.”

In these quotations the following cases have been cited as evidence
in favor of contamination, and therefore calling for investigation :!

1. Polydactyl guinea-pigs (Castle, 1906). 6. Merino sheep.
2. Long-haired guinea-pigs (Castle and | 7. Fantail pigeons.
Forbes, 1906). 8. Dutch rabbits.
3. Spotted guinea-pigs and rats (MacCurdy | 9. Picotee and other types of sweet peas.
and Castle, 1907). 10. Flowering time in peas (Hoshino, 1915).
4. Englishrabbits (Castleand Hadley, 1915). | 11. Unspecified case in swine.
5. Poultry, plumage and toe characters |12. Variegated pericarp in maize (Hayes,

(Bateson and Davenport). 1917).

Before we can discuss some of these cases intelligently it is neces-
sary that we make sure what Castle means by the terms ‘‘gametic
purity”’ and “‘unit-character.”” Unless these terms are understood
in such a way as to eliminate from consideration the idea of reeombina-
tion of independent factors there is, of course, nothing to discuss.
If by gametic impurity or inconstancy of unit-characters is meant that
recombination of modifying factors occurs, the existence of such phe-
nomena must be granted at once—this is, in fact, the main contention
of the school of ‘‘pure line”’ advocates or ‘‘mutationists.”” I think the
two following quotations from Castle are sufficient to show that there
need be no disagreement on the question of defining these terms:

“What we want to get at, if possible, is the objective difference between one
germ-cell and another, as evidenced by its effect upon the zygote, and it is

1The rough-coated guinea-pig was formerly cited (e. g., Castle and Phillips, 1914), but is now
never used. This is because Wright (Castle and Wright, 1916) has shown the results to be due
to multiple factors.

AN ANALYSIS OF THE EFFECT OF SELECTION. 41

the constancy or inconstancy of these objective differences that I am dis-
cussing. If these are quantitatively changeable from generation to genera-
tion, then change in the variability of the zygote composing a generation
might arise without factorial recombinations.”! (Castle, 1914a.)

“The head, the hand, the stomach, stomach-digestion, these are not unit-
characters so far as any one knows. But if a race without hands were to
arise and this should Mendelize in crosses with normal races, then we should
speak of a unit-character or unit-factor for ‘hands,’ loss of which or variation
in which had produced the abnormal race. But in so doing we should refer
not to the hand as an anatomical part of the body nor to the thousand and
one factors concerned in its production, but merely to one hypothetical factor
to which we assign the failure of the hand to develop in a particular case.
It is immaterial whether we call this a wnit-character or unit-factor or use both
terms interchangeably . . . . .”’ (Castle, 19160, p. 100.)

1. PotypactyL GuInea-Pics.

The most extensive data on this case are apparently in the paper
(Castle, 1906) cited in the quotation already given. The extra-toe
character was at first irregular in appearance, but was improved by
selection. In five generations, without very close inbreeding, a practi-
cally uniform race was obtained. When crosses to normal were made,
the F, results varied from nearly all normal to nearly all polydactylous.
F, contained both normal and extra-toed individuals. It is pointed
out by Castle in this paper that the results are very similar to those
obtained by Bateson from polydactylous fowls. Bateson’s comment
on that case is given below.

In the absence of any definite data regarding F, counts, the case
as reported is entirely explicable on the multiple-factor view. Castle
himself said of it, five years after the publication of the above paper:

“An alternative explanation is possible, viz., that the development of the
fourth toe depends upon the inheritance of several independent factors, and
that the more of these there are present, the better will the structure be

developed. The correctness of such an interpretation must be tested by
further investigation.” (Castle, 1911, p. 101, footnote.)

So far as I have discovered, such further investigations have not
yet been reported, although five years later this case is listed as No. 1
among those that demonstrate contamination of allelomorphs.

2. LONG-HAIRED GUINEA-PIGs.

The reference given for this case (Castle and Forbes, 1906) seems
to contain the most recent and complete data regarding it.

Angora guinea-pigs appeared in a short-haired stock, apparently
as segregated recessives. On crossing to short and extracting, there
were produced some animals of intermediate hair-length, and some
unusual ratios. But similar intermediates appeared in another strain
of shorts, apparently uncrossed with angoras, thus making it highly
probable that we are dealing here with a factor already present in the

1[talics mine.

42 AN ANALYSIS OF THE EFFECT OF SELECTION.

race, and not produced by the cross of angoraXshort. The unusual
ratios are based on quite small numbers, and the authors admit that
there are difficulties in separation of the three classes, apparently
due to overlapping. Moreover, we are given the results only in total,
not from each mating separately.

Castle himself has said of this case: ‘‘ . . . a single unit-character
is concerned. Crosses in such cases involve no necessary change in
the race, but only the continuance within it of two sharply alternative
conditions.” (Castle, 1911, p. 39.)

3. Sporrep GuINnEA-Pias AND Rats.

The reference given for these cases is MacCurdy and Castle (1907).
I am unable to find in that paper any evidence regarding guinea-pigs
that bears on the question of contamination. Nothing but selection
experiments are reported. There is, so far as I am aware, no evidence
of significance in this connection in the more recent literature on
spotting in guinea-pigs.

The evidence referred to from rats is apparently that obtained from
crosses between hooded and Irish races. Hooded rats extracted
from such crosses had more extensive colored areas than the uncrossed
hooded rats. The data given by Castle and Phillips (1914) and ana-
lyzed by MacDowell (1916) show that this is true only when the hooded
race is a “‘minus” one. The ‘‘plus” hooded race becomes less pig-
mented when crossed to Irish (or to self). MacDowell has shown that
these results conform very closely to the expectations based on the
multiple-factor view.

The later evidence on the case of the hooded rat is discussed else-

where in this paper.
4. EnauisH Rassits.

The data for this case are contained in two papers (Castle and
Hadley, 1915a, 19156), in each of which the full presentation is made.
The spotting of the English rabbit is a dominant character and is
somewhat variable. A single heterozygous male, of the grade desig-
nated 2, was mated to a number of Belgian hares. 187 English young
were produced, of mean grade 2.43, and of these F; English, a buck of
grade 3.75 (only one F; English was of higher grade), was then mated
to the same Belgian hare females. 189 English young, of mean grade
2.92, were produced.

This case presents no difficulties for the multiple-factor view, since
no evidence is given that indicates the original English buck to have
been homozygous for all modifying factors, or that prevents us from
supposing the Belgian mother of the F, buck to have transmitted more
plus modifiers to him than were present in his father. Under the
circumstances, it would have been very surprising if the two lots of
young had been of the same mean grade.

AN ANALYSIS OF THE EFFECT OF SELECTION. 43

5. PLuMace AND Tor CHARACTERS IN POULTRY.

We are referred to the observations of Bateson and Davenport
for these cases. In one instance it is stated that Davenport has shown
that ‘imperfection of dominance” and of segregation are the rule in
poultry. The question of imperfection of dominance is not apropos
in this connection. As Castle has said, regarding another case:

WS 5 . if black is crossed with brown, the crossbreds are apt to develop
in their coats more brown pigment granules than do homozygous or pure
blacks. Nevertheless, we have no reason to question the entire purity of
the gametes, both dominant and recessive, formed by such cross-bred black
animals. It is the dominance, not the segregation, which is imperfect.”’
(Castle, 1911, p. 91.)

That F, results do not bear on the question has been shown by
Bateson (1909), who says with regard to polydactylous fowls:

“Tt might be pointed out that when, as in these examples, the abnormal
result is clearly perceptible in F,, no question arises as to the occurrence of
an imperfect segregation. The peculiarity is evidently zygotic, and is caused
either by some feature of zygotic organization, or by the influence of external
circumstances.” (Bateson, 1909, p. 251.)

Moreover, in any case involving irregularities in dominance, im-
perfect segregation in crosses between different breeds would be very
difficult to demonstrate.

6. MERINO SHEEP.

No reference to the data in this case are given. I have been unable
to discover anything more definite than a few general statements by
practical breeders regarding the effects of crossing Merinos.

Bateson admits, in the passage quoted above, that this and the
next case ‘‘may be ascribed to the interference of a multitude of

factors.”
7. FANTAIL PIGEONS.

This case has been studied by Morgan (Morgan, Sturtevant, Muller,
and Bridges, 1915, p. 186). The fantail type did not reappear in the
comparatively small F, generation, but individuals not far from the
fantail were obtained; and when the F,; hybrids were mated to fan-
tails, several of the offspring fell within the range of the fantail race.
Bateson’s “‘failure of a parental type to reappear in its completeness
after a cross” is, then, scarcely applicable to this case.

8 anp 9. DutcH Rassits AND Cases IN SWEET Peas. FRACTIONATION.

These are the specific cases cited as illustrations of Bateson’s theory
of “fractionation” or ‘subtraction stages,” of which he states that
‘it is to be inferred that these fractional degradations are the con-
sequences of irregularities in segregation.” In the case of the sweet
pea, Bateson has pointed out that white flowers and the extreme dark

44 AN ANALYSIS OF THE EFFECT OF SELECTION.

flowers of the deep purple Black Prince were among the earliest varia-
tions to appear, while the intermediate forms have arisen later, as he
suggests by fractionation. It would seem to follow that they have
arisen in heterozygous forms, for otherwise the fact that the larger
variants appeared first would be of no significance. There is, I think,
no evidence to show that the later variations did actually arise in
heterozygous forms, either in sweet peas or in rabbits. These factors
are all inherited separately, and this fact would seem to rule them
out of consideration if one adopts the chromosome theory of inheritance
or if one appeals to multiple allelomorphs as evidence in favor of the
variability of genes. In short, we have no evidence regarding the
origin of these forms, and their present behavior seems to indicate
that they are not due to fractionation. The only evidence in favor
of such a hypothesis is the somatic appearance of the characters.

10. FLowERING TIME IN P2ras.
Castle (1916a, p. 324) has summarized this case as follows:

“Hoshino (1) recognizes that gametic contamination results from cross-
ing early and late flowering varieties; (2) recognizes also that variation may
occur among the cross-bred families, as well as in different pure lines of the
uncrossed races, as regards the ‘quality,’ value, or potency of the same gene;
(3) although Hoshino does not refer to the fact, his observations show clearly
that genetic variation of a gradual or fluctuating sort occurs in at least one
of the varieties which he crossed.

; What I want to suggest is that in these several agencies we
have a sufficient explanation of the variation observed in Hoshino’s Fe, Fs,
and F, generations, without invoking a two-factor hypothesis (as Hoshino
has done), one factor being enough.”

Castle’s argument is that a difference in one pair of genes is sufficient
to account for the result, if contamination be assumed; and that one
difference is a simpler assumption than two. I have argued here that
such an assumption is not simpler, unless we can find positive evidence
that contamination ever occurs. In the present case, then, we must
turn to the evidence that led Hoshino to suppose contamination to
have occurred.

Hoshino crossed an early-flowering pea and a late-flowering one.
The F, was nearly as late as the late parent; F:, obtained by self-
fertilizing F,, approximated fairly closely to 3 late :1 early, but the
two classes were somewhat more variable than the corresponding
parent varieties, and apparently overlapped slightly. Hoshino self-
fertilized 236 of these F, plants and obtained 46 families that he
classified as constant, 7. e., supposedly homozygous. This is a fair
approximation to the 1 in 4 expected if two pairs of genes are respon-
sible for the result. Hoshino shows that two pairs of genes will, in fact,
account for most of the results obtained. There are certain facts not
thus accounted for, but Hoshino shows (p. 265) that “‘secondary”’

AN ANALYSIS OF THE EFFECT OF SELECTION. 45

modifiers (7. e., modifiers producing only small effects) will account
for all these facts, with a single exception. Three families were ob-
tained from F, plants that must, on the two-factor view, have been
of the same constitution. These plants were heterozygous for one
pair of genes only. They produced, in F;, the same type of later
constant (homozygous) families, but differed slightly in the flowering
times of the earlier constant families produced. According to Ho-
shino’s view, if the earlier types differed the later ones should have
differed in the same direction, because they must have received the
same ‘‘secondary modifiers.” This objection is not valid, for specific
modifiers that act only in the presence of certain other genes are well
known (see especially Bridges, 1916), and are sufficient to account
for the differences observed. This argument is the only one that
Hoshino gives to support his conclusion that contamination must
have occurred. We must then conclude that the case does not furnish
positive evidence for contamination, since it is explicable without re-
course to that hypothesis.!

11. UnspeciFIeD CasE IN SWINE.

This case is cited by Castle (1916b, p. 215), but no references or
authorities are given. It appears, however, from the legend under fig-
ure 93 (opposite p. 139) that the belted character is the one referred to.
The only data bearing on this case that I have found are presented by
Spillman (1907), and consist of information supplied largely by prac-
tical swine-breeders. Spillman himself interpreted the case as one in
which two factor-pairs are involved. The data also suggest the pos-
sibility that we are dealing with a case of ‘imperfect dominance”’ simi-
lar to those in poultry. At best, the data are meager and indefinite.

12. VARIEGATED PERICARP IN MAIZE.

The paper of Hayes (1917) referred to above should be studied
in connection with those of Emerson, particularly his full paper (Emer-
son, 1917), dealing with the same character. These two workers have
shown that there is a remarkable series of multiple allelomorphs in
this case, and Emerson has shown very clearly that some of these
allelomorphs mutate quite frequently—the only established instance
of the sort.

1We are not here directly concerned with Castle’s contention that Hoshino’s results prove
the effectiveness of selection within a pure line. I can not, however, refrain from a few comments
on that contention. Castle states (1916a, p. 324), in connection with the differences in flowering-
time between the offspring of early and late flowering sister-plants: ‘‘ From long experience in
studies of rats with such small differences as are here indicated I have no hesitation in concluding
that fluctuating variation of genetic significance is here in evidence.’’ One wonders how ex-
perience in dealing with differences in pigmentation in rats can give an observer special ability
in determining by inspection the significance of three-tenths of a day difference in the flowering
time of peas. With respect to Castle’s calculations from Hoshino’s data, it may be pointed
out that the greatest favorable difference recorded, 1.27 days, is incorrect, and should read 0.26
day. In view of the fact that there is no guarantee that the material used was homozygous,
I have thought it scarcely worth while to recalculate all the differences, or to determine their
probable errors; but it is certain that the probable error of each difference is of the same order of
magnitude as the average difference itself, 7. e., about 0.3 day.

46 AN ANALYSIS OF THE EFFECT OF SELECTION.

Hayes has, by selection from a mixed population, established four
different grades of variegation (including self-colored and colorless)
that breed true and that represent four allelomorphs. The two in-
termediate types, ‘‘mosaic” and ‘“‘pattern,’’ are the ones of special
interest in the present connection. When these two types were
crossed, the mosaic type was dominant, but there was an increase in
variability in F, and some individuals with more pigment than either
parent were obtained. The parent races had been selfed and selected
for about six generations before the cross was made. In view of the
great amount of heterozygosis that seems to be normally present in
maize, and the large number of chromosome pairs (20?), this seems to
be hardly sufficient to make certain that both races were pure for their
modifiers. ‘The increased variability of F, is therefore not surprising;
and that phenomenon would of course be expected to be followed by
a still greater increase in variability in F). Such an increase was, in
fact, observed, and is the chief basis for Hayes’s conclusion that con-
tamination may occur. The data are not sufficient to demonstrate
that new allelomorphs arise more often in heterozygotes than in homo-
zygotes; and even if it be shown that they do so, it does not follow that
there has been contamination of allelomorphs. There are too many
unknown factors involved in the production of these new allelomorphs
for such a conclusion to be valid without very careful controls.

It appears from the foregoing review that the cases cited as illustra-
tions of contamination of allelomorphs or imperfect segregation are
all explicable on the multiple-factor view, or rest on extremely indefinite
data.

One series of data bearing on the question has been presented in
this paper (p. 32), and has been interpreted as giving evidence against
contamination. Three other cases have been worked out by Muller
(1916) and Marshall and Muller (1917). Muller kept three mutant
characters of Drosophila in heterozygous condition for about 75
generations. The factors were kept constantly in flies heterozygous
for their normal allelomorphs, so that the characters remained unseen
for a long time.

Muller extracted one of these characters (dachs) from this stock,
and measured the tarsi, using the length of thorax as a standard of
comparison. Dachs flies are characterized by shortened tarsi; and
the flies from the heterozygous stock were found to have tarsi actually
a trifle shorter than those found in a stock that had been kept pure for
dachs. This result was not very conclusive, chiefly because it was
based on a very few flies.

Marshall and Muller made much more extensive studies with the
wing characters, curved and balloon, derived from the same heterozy-
gous stock. They obtained a similar result; the wings were no nearer

AN ANALYSIS OF THE EFFECT OF SELECTION. 47

the normal than were those of curved and of balloon flies that had been
kept in pure stocks. These results, taken in connection with the data
presented above for bristle number in flies from lines heterozygous
for Dichet, furnish definite evidence against contamination of allelo-
morphs in heterozygous forms.

CastTLe’s EXPERIMENTS witH Hoopep Rats.

Perhaps the best known selection experiment is that carried out by
Castle and various collaborators (Castle and Phillips, 1914, Castle
and Wright, 1916, ete.) with hooded rats. The theoretical conclu-
sions reached by Castle are not in agreement with those arrived at
by various other investigators, including the author, although for the
most part the data obtained are very similar. Castle’s results have
been discussed by Muller (1914a) and MacDowell (1916), who have
shown in detail that all the data known to them were explainable on
the multiple-factor view, without recourse to such hypotheses as
contamination of factors or production of factorial variations by selec-
tion. One point has, I think, not been sufficiently emphasized by
them, namely, that the rat experiments are hard to evaluate properly
until we are in possession of more accurate data regarding the pedi-
grees. Since these two criticisms were written, Castle (Castle and
Wright, 19f6) has given some additional data, which he has used,
in a reply (Castle, 1917) to MacDowell’s paper, as arguments against
the latter’s conclusions.

With regard to the question of pedigrees, to take up these ques-
tions in order, the main point on which information is desired is:
How closely inbred were the rats, both before and after the beginning
of the selection experiment? The following quotations contain most
of the available evidence on this matter:

“Since the entire stock is descended from a very few individuals (less than
a dozen), and we have at no time hesitated to mate together brother and
sister, provided they varied in the same direction, but have always used the
most extreme individuals (plus or minus) which were available, to mate
with each other, it follows that very close inbreeding must have occurred
throughout the experiment.’’ (Castle, 1914b.)

“Tt is impossible for a colony of 33,000 rats to be produced from an original
stock of less than a dozen animals, with constant breeding together of these
which are alike in appearance and pedigree, and with continuous selection of
extremes in two opposite directions, without the production of pedigrees
which in the course of each selection experiment interlock generation after
generation and finally become in large part identical with each other. This
has been repeatedly verified in individual cases, but is incapable of a more
generalized statement or of demonstration in generalized form. At least I
am unable to devise such demonstration.” (Castle, 1916d.)

Elsewhere (Castle and Phillips, 1914, p. 20) it is stated that part
of the original stock consisted in a mixed lot of trapped rats that “had
probably arisen by the crossing of an escaped albino rat with wild

48 AN ANALYSIS OF THE EFFECT OF SELECTION.

ones.” We do not know where the rest of the stock came from, and
we do not know how the animals used to start the selection experi-
ments were derived from these sources. We do not know how many
individuals were used to start the selection experiment; and we do not
know anything as to the relationship between the rats in the two series
(plus and minus). And, finally, we have only very indefinite data
as to what system of breeding was followed during the experiment.
All this information is very much needed, if we are to know how to
interpret the results. It is conceivable that each series was split up
into a number of separate lines, and that these have been crossed
from time to time. Such a system would result in bringing together
modifying factors more slowly than would a system of very close in-
breeding. It is, of course, very improbable that any such system has
been followed; and such an assumption is by no means necessary for
a multiple-factor interpretation of the results. But definite informa-
tion is very desirable, as is indicated by an analogous case.

In connection with certain work that the writer has been carrying
on with Mr. J. W. Gowen, pedigrees of the two famous thorough-
bred race-horses, Sysonby and Artful, have been tabulated. These
pedigrees are both practically complete for 10 ancestral generations.
They constitute a fair random sample of pedigrees in the breed, for
Sysonby was of pure English blood, while Artful had many American-
bred ancestors. The two pedigrees show no name in common until
we reach the fifth ancestral generation. In that generation there are
three names that appear in both pedigrees. But by the time we reach
the tenth ancestral generation, approximately 90 per cent of the 1,024
names in Artful’s pedigree appear also in the first ten generations of
Sysonby’s pedigree. And the result would certainly be even more
striking if the pedigrees were studied for a few more generations, or
if two English-bred horses were compared. Here, then, we have a
clear case of ‘‘interlocking” pedigrees. Yet in spite of the long in-
breeding (12 to 20 or more generations, with scarcely any out-crosses)
which the breed has undergone, there are still a large number of bay
or brown and of chestnut race-horses, besides a few grays and blacks.
Of the four Mendelian factor pairs (see Sturtevant, 1912) for which
the race was originally heterozygous, it has become homogeneous only
in that the roan factor has been eliminated.’ Clearly, selection for
any one of the colors now present would still be effective in eliminating
the others. The breed, which we may suppose to be inbred to some-
thing like the same degree as Castle’s hooded rats, is still very far
from a ‘“‘pure line.”

The new data presented by Castle and not taken up by MacDowell
consist of two points: The crosses of extracted hoodeds (from plus

‘Even in the early days roan race-horses were not at allcommon. Both roan and gray have
been selected against.

AN ANALYSIS OF THE EFFECT OF SELECTION. 49

race Xwild) to wild, and the relations of the ‘‘mutant” series to the
selected series.

When the plus race was crossed to wild, and F, hoodeds were ex-
tracted, it was found that in these extracted animals the mean grade
was lighter (less ‘‘plus’’) than that of their selected grandparents.
This, as MacDowell pointed out, is the expectation on the multiple-
factor view. But Castle now states that when these extracted hoodeds
are again crossed to wild, and hooded is extracted once more, the
twice-extracted hoodeds are about midway in mean grade between
their extracted grandparents and the uncrossed plus race. As he says,
the wild race might have been expected to bring these animals still
farther away from the plus race if modifying factors were involved.
Evidently it is very important that we know as much as possible about
the wild rats used in these experiments, in order that we may know
what they were likely to carry in the way of modifying factors. These
rats, we are told, all came from the same stock, which was trapped at
the Bussey Institution in large numbers and was reared for two gen-
erations in the laboratory. ‘‘In making the second set of crosses, the
extracted individual has, wherever possible, been crossed with its own
wild grandparent.’”? An examination of the table given shows that
not more than 102 of the 256 twice-extracted hoodeds can have been
produced in this way, unless individuals of the same sex were mated
together. Just how many of the 102, and which ones, does ‘‘ wherever
possible” include? How many wild rats were used in the original
crosses? These questions are important, because it is evident from
a study of the data that the result emphasized by Castle is due almost
entirely to the descendants of one original plus-line female; 41 of the
73 once-extracted hoodeds were F,’s from this female; and their mean
grade was 3.05, as against 3.3 for the remaining F’s, and 3.17 for the
generation as a whole. The twice-extracted hoodeds tracing to this
female were of mean grade 3.47, while those from the other original
hoodeds were again of approximately grade 3.3. Further data re-
garding the pedigree and other descendants of the mates of this female
and of her grandchildren are very much needed. Informe tion regard-
ing the ancestry of the female herself would also be interesting.

It should also be pointed out that this case, accepted at its face value,
is difficult to explain on the view that the hooded-rat results are pro-
duced solely by variations in the hooded factor itself. On that view
the changes brought about by crossing are usually referred to con-
tamination of the factors in the heterozygote. But that interpretation
leaves entirely unexplained the results of the first cross to wild. If
the hooded factor is contaminated by its allelomorph, the once-
extracted hoodeds should be darker than their grandparents, whereas
in reality they are lighter, as would be expected on the multiple-factor

50 AN ANALYSIS OF THE EFFECT OF SELECTION.

view. Castle has met this objection in the following manner (Castle
and Wright, 1916):

“This suggests the idea that that loss (of ‘plus’ character) may have been
due to physiological causes non-genetie in character, such as produce in-
creased size in racial crosses; for among guinea-pigs (as among certain plants)
it has been found that F, has an increased size due to vigor produced by
crossing and not due to heredity at all. This increased size persists partially
in F,, but for the most part is not in evidence beyond F;. I would not sug-
gest that the present case is parallel with this, but it seems quite possible
that similar non-genetic agencies are concerned in the striking regression of
the first F, and the subsequent reversed regression in the second F>».”’

This comparison seems to me to be rather far-fetched, and I am
quite unable to understand the hypothesis of ‘‘non-genetic physiologi-
cal causes.’”’ That they are “physiological” is, of course, obvious;
but they depend for their appearance on the pedigree of the animal,
and they are persistent to F,, so why ‘‘non-genetic’”’? The results
from size crosses are entirely explicable on the basis of Mendelian
modifying factors, so why need one appeal to vague ‘‘non-genetic,”’
yet transmissible, factors? And is not such an appeal, in principle,
an appeal to modifying factors? It certainly involves the assump-
tion that the grade depends on transmissible material other than the
hooded factor itself.

In the tenth generation of Castle’s plus selection series there ap-
peared two rats of considerably higher grade than any individuals
of that series previously recorded. These individuals were shown
(Castle and Phillips, 1914, pp. 26-31) to differ from the plus race by
a single dominant factor. This has been taken by MacDowell to
indicate that a new modifying factor arose by mutation. But Castle
has now presented evidence indicating that the mutation occurred
in the hooded locus itself. When homozygous “mutants’”’ were crossed
to wild rats, F: consisted in self-colored rats and rats of the same grade
as the mutant series—no hooded individuals. (Castle and Wright,
1916.) Castle (1916) concludes from this evidence: ‘‘This serves
to confirm the general conclusion that throughout the entire series
of experiments with the hooded pattern of rats we are dealing with
quantitative variations in one and the same genetic factor.’’ Now,
the “mutant” variation differs from the other results obtained by
Castle in two respects: It appeared suddenly, as a definite and very
slightly variable character, and it fails, when crossed to self, to give
normal hooded in F,. Because of the first point, it is probable that
it arose during the experiment as a new variation; because of the sec-
ond, it is probable that it is a variation in the hooded factor itself.
Since these conclusions as to its nature are based entirely on the points
in which it differs from the remainder of the results, it is difficult to
see how Castle’s case for these results is in any way improved. On
the contrary, if this is the behavior to be expected of a new variation

AN ANALYSIS OF THE EFFECT OF SELECTION. 51

arising in the hooded factor, then the “‘mutant”’ variation is evidently
the only case of that sort that Castle has reported.

GENERAL CONCLUSIONS.

That many characters may be influenced by more than one pair of
genes has long been recognized, and this is the essence of the multiple-
factor view. That genes exist which require the action of other genes
before they produce visible effects has also been long known. Further-
more, that there are genes which produce very slight visible effects
is now another commonplace. Given these three facts, and the
hypothesis (which is supported by much specific evidence) that most
races are heterozygous for a number of such genes is all that is re-
quired to complete the conception that is held by most adherents of
the view that multiple factors or modifying genes are responsible for
the results of selection.

In specific cases, the existence of definite modifying genes has been
demonstrated by Dexter, Bridges, Muller and Altenburg, and the
author. All other data in question fit in with the view that selection
ordinarily acts only by isolating modifiers.

Modification of factors by selection, crossing, fractionation, or
similar means is undemonstrated in any given case, and has been
shown not to occur in other cases that are typical of the results usually
obtained. Factors do change, and more than two forms are possible
for certain loci; but there is no known method of inducing such changes,
and they are ordinarily quite rare and definite.

SUMMARY.

(1) Dichet is a dominant character, the gene being lethal when
homozygous (yellow-mouse case). The gene is in the third chromo-
some.

(2) Dicheet flies are more variable in bristle number than are not-
Dichets. This variability is partly environmental, partly genetic.

(3) Selection was effective in isolating both plus and minus Dichet
lines.

(4) A cross between two separate inbred plus lines gave no increase
in variability and no increase in parent-offspring correlation. There-
fore the two lines were presumably of very similar constitution, though
independent in origin.

(5) A eross between an inbred plus line and an inbred minus line
gave the results characteristic of such crosses—increased variability
in F, and increased parent-offspring correlation.

(6) Linkage tests demonstrated that modifying genes exist in the
selected lines. Several lines were shown to differ in one or more sec-
ond-chromosome modifiers, and at least one of these modifiers was
shown to cross over from the speck gene.

52 AN ANALYSIS OF THE EFFECT OF SELECTION.

(7) In one case at least one third-chromosome modifier was shown
to exist and to cross over from Dichzet, which must lie to the left of it.

(8) Two third-chromosome lethals were obtained. These were
shown to be new mutations, not due to fractionation of the Dichet
gene.

(9) A new allelomorph of Dichet, called Extended, appeared in a
plus selected line. It is argued that this mutation was not due to
fractionation of the Dichet gene, and was not influenced by the selec-
tion that was carried on.

(10) Another character, somatically indistinguishable from Ex-
tended, was shown to be due to a recessive second-chromosome gene.

(11) A study of unselected Dichets, and of the not-Dichxts pro-
duced by long-continued mating together of Dichets, is shown to fur-
nish evidence against the view that allelomorphs are contaminated in
heterozygotes.

(12) A general discussion of the selection problem is divided into
three parts: (a) an attempt is made to clear up certain current mis-
understandings and disagreements as to what questions are really at
issue; (b) cases cited as evidence for contamination of allelomorphs
are discussed in detail, and the conclusion is drawn that contamina-
tion is unproved and is an unnecessary hypothesis, with some direct
evidence against it; (c) certain specific objections are raised to argu-
ments made by Castle on the basis of his experiments with hooded
rats.

BIBLIOGRAPHY.

Bateson, W.
1909. Mendel’s principles of heredity. 2d impression, Cambridge.
1914. Address of the president of the British Association. Science, n. s., 40.
Bripags, C. B.
1915. A linkage variation in Drosophila. Jour. Exper. Zool., 19.
1916. Non-disjunction as proof of the chromosome theory of heredity. Genetics, 1.
Catxins, G. N., and L. H. Gregory.
1913. Variations in the progeny of a single ex-conjugant of Paramecium caudatum.
Jour. Exper. Zool., 15.
Caste, W. E.
1906. The origin of a polydactylous race of guinea-pigs. Carnegie Inst. Wash.
Pub. 49.
1911. Heredity in relation to evolution and animal breeding. New York.
1914a. Multiple factors in heredity. Science, 39.
1914b. Variation and selection; a reply. Zeitschr. Abst. Vererb., 12.
1916a. New light on blending and Mendelian inheritance. Amer. Nat., 50.
1916b. Genetics and eugenics. Cambridge, Mass.
1916c. Report in Carnegie Inst. Wash. Year Book No. 15.
1916d. Can selection cause genetic change? Amer. Nat., 50.
1917. Piebald rats and multiple factors. Amer. Nat., 51.
and A. ForBszs.
1906. Heredity of hair-length in guinea-pigs and its bearing on the theory of pure
gametes. Carnegie Inst. Wash. Pub. 49.
and P. B. Haney.
1915a. The English rabbit and the question of Mendelian unit-character constancy.
Amer. Nat., 49.
1915b. Same. Proce. Nat. Acad. Sci., 1.
and J. C. Puirures.
1914. Piebald rats and selection. Carnegie Inst. Wash. Pub. 195.
and 8. Wricar.
1916. Studies of inheritance in guinea-pigs and rats. Carnegie Inst. Wash. Pub. 241.
Dexter, J.S.
1914. The analysis of a case of continuous variation in Drosophila by a study of its
linkage relations. Amer. Nat., 48.
Emerson, R. A.
1917. Genetical studies of variegated pericarp in maize. Genetics, 2.
Hayes, H. K.
1917. Inheritance of a mosaic pericarp pattern color of maize. Genetics, 2.
Hosurno, Y.
1915. On the inheritance of the flowering time in peas and rice. Journ. Coll. Agr.
Tohoku Imper. Univ., Sapporo, Japan, 6.
Jenninas, H.S.
1916. Heredity, variation, and the results of selection in uniparental reproduction
in Difflugia corona. Genetics, 1.
JOHANNSEN, W.
1903. Ueber Erblichkeit in Populationen und in reinen Linien. Jena.
Lirttg, C. C.
1915. The inheritance of black-eyed white spotting in mice. Amer. Nat., 49.
Lutz, F. E.
1911. Experiments with Drosophila ampelophila concerning evolution. Carnegie
Inst. Wash. Pub. 148.
MacCurpy, H., and W. E. Castip.
1907. Selection and cross-breeding in relation to the inheritance of coat-pigments and
coat-patterns in rats and guinea-pigs. Carnegie Inst. Wash. Pub. 70.

53

54 BIBLIOGRAPHY.

MacDoweE tt, E. C.
1915. Bristle inheritance in Drosophila. I. Extra bristles. Jour. Exper. Zool., 19.
1916. Piebald rats and multiple factors. Amer. Nat., 50.
1917. Bristle inheritance in Drosophila. II. Selection. Jour. Exper. Zool., 23.
MarsuHat., W. W., and H. J. Mutter.
1917. The effect of long-continued heterozygosis on a variable character in Droso-
phila. Jour. Exper. Zool., 22.
MIppDLerTon, A. R.
1915. Heritable variations and the results of selection in the fission rate of Stylonychia
pustulata. Jour. Exper. Zool., 19.
Moraay, T. H., A. H. Sturtevant, H. J. Muuurr, and C. B. Brinces.
1915. The mechanism of Mendelian heredity. New York.
Motter, H. J.
1914a. The bearing of the selection experiments of Castle and Phillips on the variability
of genes. Amer. Nat., 48.
1914b. A gene for the fourth chromosome of Drosophila. Jour. Exper. Zool., 17.
1916. The mechanism of crossing over. Amer. Nat., 50.
1917. An Oenothera-like case in Drosophila. Proc. Nat. Acad. Sci., 3.
Pearson, K.
1911. On the probability that two independent distributions of frequency are really
samples from the same population. Biometrika, 8.
Spruuman, W. J.
1907. Inheritance of the belt in Hampshire swine. Science, n. s., 26.
Sturtevant, A. H.
1912. A critical examination of recent studies on color inheritance in horses. Journ.
Genet., 2.

DETAILED DATA.
TasBLe 25.—INBRED Pius Series. 864 Line.

Parents.

Genera-

tion and

culture

No.

F, 893 |6| 7 BOS || sata sietellicotel| state le spell Seatsy| SLO Srarel| S27 «4A OG| Nee ALON e cles « ..- {113
F, 902 |7|6 893 ASB OW SiPLF | Weeeeie cele: 61
903 | 7| 6 893 |. Di Ole Oye aie Were La ale Se ee 70
F; 926|6]|6]| 903 Be hese | erzienG ROS he eee a ppalNice3
F, 1006 | 6 | 6 926 |. US aL 2 AOE 2320 hs ea eat: ile cae, . ... {108
1013 | 6 | 6 926 |. 1 25] 24) 26) 27) 28) 21)...)...]... 152
F; 1064 | 6 | 6 | 1006 Deal Ges) | LOW moles ilecuheec 48
1081 | 6 | 6 | 1013 |. De TAN Ade eel ol tate 26
1084 | 6} 6 | 1013 |. 9} 656] 21) 9 11) 20).. 75
F, 1153 | 6 | 6 | 1064 |. ete |r| AAG re cieicltcce-< 12
1170 | 6 | 6} 1081 |. D2 |Ol xGltadth aL eacilhes. 21
PEON Ge Ba OBL ais. a)'. cis] «<1 ce) Meme: 4 a Beg er 15 f ai V2) ee ee | 87
F, PZSOWIGe! GO PLS S ye crit eei|ieere Rragel|lorare)| NetIMme htolh Reel tare Zi Sevellerers 17
7 eG MGR EL Olath is. fs\ Brora llavere L4| 620) 16 |LOG) 16 |e) sacle eee 92
ad zy (ajo (eatin es BY Sa A Vat! loca Bee Ghs 4 OLS AS WAS apes oles 68
PASS MG 1G | MLO eer eserel| evetei| (stone ~f 28), 19) LAP 2Ol 22h ASS eee wees 124
T2998) OMG] LEON re olereseilletess|\stere Rech [eres bai per} | 3 \0R3 2) | ires Fe ee 33
1309 | 6 | 6 | 1170 -| 10} 6) 4} 14) 16) 19). 69
1318 | 6 | 6 | 1191 M8), VSP Waka 60
19225) (6) Gy VIO |e | 6} 5) 7| 12) 5} 12). 47
F; 1384. |\6)|.%) | L239)... 1}. 3). 3) Zi) 8 5 alee
13905), GiGi 277i. |e. SSP De Ole Seale ll .| 25
1406) GuyGe) boise |. ace 4) 1) 4) 4 6) 5}...1. 24
1420 | 6 | 6 | 1298 }...]... 1) 2) 4 5) 5 4) Qj. 22
$421) 66) 12980). oe. 1} 13} 16] 16] 14} 21] 14]...]. 95
4422.1 6>| 6 | 1299 )...|/-.. 1} 1) 11) 6) 38] 35).. 92
1430) 75) (63) T2878 oe. 3] 2) 10) 6) L722). 31... 60
1431 | 6 | 6 | 1309 7 ea ea 3 Ha Vege 3 (0 ad | eh Ue 21
PASE) Gi thee ea ea, cre fetal easel] eee aille gets lec re flcrets lellferote]| int | eke] ON 21) eM eees | ees 27
FEBS AG Gt M28 Feil feteil te esell ereie\l's,ste'|/«/ar<i] syste ayoy|l skatsl| veda Cle dlcta| eral bballoce 13
1478 | 6 | 6 | 1298 |.../... SL 7! 10) SOL Tiles Tee seers eee 60
F, PEED 6) |) Sil) T3890 Elsie: Zeta okt 13) AON eel ee ee 15
2576) | 6 6.) VA ik: Si ah S]) GLAS eo te We: oe ee. 55
1613: |/6:| 6x) 1459) |. alive aN Ue VCO DAd er em cls 53
1629 | 7 | 6 | 1444 ]...]... Heal ie S| lead |S les less rei] ens alpaca eee 10
1690 || 7 |\'6)| 1478)... ale. OAS ale RE Od oat louelleeal eee ee 21
Fy 1663) | 6!) Ge) PSE). .4).... Seal USS alto head)! Bless elle 11
1763) |)6) })'G-))) L643; 2 a). 22 De 3 Vi] De ae 4 i eee) et | 37
BELO) | 6 || 6.) 1613) |... .|-... 1 8] 20) 14] 18} 17) 18) 15)... ee lll
En 1887 | 6} 6} L763: |. al. 2] 4 )) SG 1O| 24 AD he ciloc-olee «ileus 57
1890 | 7 | 6 | 1763 |...|... 1 3) 4 Sl Oi Ol AS ee cee sie, 58
1944.16) G6"), 18104). J... 2 dl rd || L419 GP By reer epee | Poe cll ever 65
1963! | 16.)6) | 18108)... 2) 4 Sib) Gl Ale Dee Ie ahs. cilaests 29
1982'| 6 | 6 | 1810 .). . |... EET (Oeape d Nhewe’ P )Wa )| PE 1110S al ee a a 23
Fy 2013 | 6 | 6 | 1887 2 5) 14), 16) 21) 22) 20h EN a She. ee 95
2027 | 6 | 6 | 1887 aratsllovehoilacetel! Ol eer Reol CL aes ees 47
2028 | 6 | 6 | 1890 |. kop a flaneysi teed | ce eS |e ters cltien hPa eee 34
2029 | 6 | 6 | 1890 |. C2} fe lated Ned Ven Cs) ins Cy |s C1 eh Ua ah |e 78
2060 | 6 | 6 | 1887 |. 1 Al ONY Gil cSt OleaQ eZ Tee se 2 ee 70
2061 | 6 | 6 | 1890 |. Ll Al 4h OAS LA eee leas 65
2062 | 6 | 6 | 1890 nvols|llokexelllatetei|| a SPkI) ece3| teaeah|lecbcalllnvessihare alllenza tf
2087 | 6 | 6 | 1887 |. ANA PSTD UT Oh | Wie cles 50
2098 | 6 | 6 | 1944 |. ripe) Rc ert Pe tbe 1M UP Up | 30
2105 | 6 | 6 | 1887 |. 1 4) YS) SO} OV CRE Bote. ol be ie 2 71
2115 | 6 | 6 | 1944 Lo Bes Ph ea cevcitie erates 25
PAPE ayy Galles iMies Ale sal Boellene| eacllood sac 3} 5) 3) 4 15
21422156) PGs slSSip esa so ston ees 1 LL 2|) 2319 17, 44

10ffspring not separated for sex. 22d brood of 2087.

56 AN ANALYSIS OF THE EFFECT OF SELECTION.

Taste 25.—INBRED Pius Serres. 864 Line—Continued.

Genera Parents. 1 2 3 4 5 6 7 8
tion and
culture | Grade.) Q.y 3
No. ee PIFIPIL PI SI PI SI APTI SI A[ AISI AISI QI aA] ©
Q\|a 4 B
Hig 2132) Fi] Gi) SOLS Ge a! oc a alec ce A) 2). |) BIAS ||. calbscle 15
DAVEE iy ONE OA DPE IB slo al lane a|leee clita ol lace AR a eae tears) feat 2 VP PS 9 Peet 64
STAG Gi ea ee Lean ea falllovasei)~ sop enate oleate LBS S12 lela fe evel Rul tare 53
DUST eG) LOCO. fells acatl aa zaifce rote el 2 || 8h) M6 20iesl) c4ee 72
DUO! Guu) SOGZ i ter cates jellies < cell ence Sil esc] Py wall eg al ones) ee 2] een | IG Th 4) ea let rel ee =| fc ks
Q2I9T | FS Gr) 2O9Sal ells che sel os Pas 3] 6]) SS tG Ol) BU 2 ie eralttere|| OO
ODEN | egal seLOSE a yctellieretaltccell = <tellisvecel|(exeel|f) Ll lart)] niete DD Ee exci| lava 18
DRANG G5] era ea LONI eo 4| (eh etts|| areitsi| takecal| ote oll fo-erteff fates S28) Ue LASS sie 37
Fy, 2248 Ga OHIS > V8 oles! Bro sl aoa esl [Biers [oo sat 3 V3 2a e26 Al gale 60
DOOR reall) LUG MAAl> tele cellars erlexesellie ous] |= evel] (ete iai] satel] (stone 1} 14; 9} 6) 8... 38
DIO48y | Gil e7|| 2AESOM Ss raillaie relies el|'= aise ells arei| |e ete | Nete ls esas tsi at eve || et] 28
DOTS Ney fal eek) Gel eels laseldodlisaol| oelieaale Pact Clie) 9 o4) Wer ailooa 31
DRT Ye nc (eral | Be feiss |store Alera eee loners) loa aces foe SIG] Wit Ie. 5. levee 18

aaa Ms i ek 0) IE | a Po FP Ne eee eee
1The original record sheet for 2304 has been lost, and the sexes are not noted separately on the
copy from which this count is taken.

TasiLe 26.—INBRED Pius Series. 1002 LINE.

G Parents. 1 2 3 4 5 6 7 8
enera-
tion and
culture |Grade. Cul- 3
No. ane QIPI PI PI ASI AMI SPI PIL PI SP/ PIP] PL AI PIA] ©
Q|a ; me
F, 1072 | 6 | 6 | 1002 |... 20| 14) 17} 21] 16) 26). 114
F, 1150 | 6 | 6 | 1072 5] 11) 15] 17] 42) 30) 1 121
1158 | 6 | 6 | 1072 1) 35} 30] 11} 12] 11] 10). 110
F, 1213 | 7 | 6 | 1150 4| 1] 14] 20) 32] 46) 1 1} 1/120
1233 | 6 | 6 | 1150 2) oh a6 ea 2 32
1247 | 6 | 6 | 1158 5] 5) 6} 11] 24) 29 80
1264 | 6 | 6 | 1150 2) Li 3} 5) 37)33) 2) 1 84
1278 | 6 | 6 | 1150 22) 28] 24] 20) 14) 22 130
F, 1347 | 6 | 8 1213 ool La LL) 2716 | S9lh2z i) 122
1348 | 6 | 6 | 1213 |) 1G) WL L6]e VS ASO Sy sad: S| Eeerlindo
1350 | 6 | 6 | 1247 1) 3] 54] 33] 34) 13] 12) 12) 1)...]...]...]163
1363 | 6 | 6 | 1213 ce | lee: SO Vf De ie UN 27
1374 | 6 | 6 | 1247 1} 1| 14) 14) 6] 6) 17) 13). 72
1375 | 6 | 6 | 1247 5 3 2) 22) 17| 11] 12) 23) 16).. 106
1383 | 6 | 6 | 1213 Bille Silos 3) 9} 16} 13). 44
1386 | 7 | 6 | 1264 eae 9} 9) 10) 5} 2) 9 44
1387 | 7 | 6 | 1264 site|, od | <4) 7) | Si) “iP Ushers -| 36
1388 | 6 | 6 | 1247 1). 5] 21) 15} 5) 18) 6) 8). .| 79
1389 | 6 | 6 | 1247 Di a al Sie Sark 14
1401 | 8 | 6 | 1213 15] 8} 6] 17) 19} 21)...). 86
1402 | 7 | 6 | 1213 6| 4) 8 4) 14) 9 Ij. 46
1403 | 6 | 7 | 1233 Dy} Al 2) Sh e22)e25). : 56
1404 | 6 | 7 | 1264 1 weil), lle 1} 5} 24) 22). 54
1419 | 6 | 6 | 1264 ...| 9] 6} 20) 12) 42) 35).. 1 125
1436 | 6 | 6 | 1264 1)...| 2) 6] 5) 22) 26). .: 52
F, 1479 | 7| 6 TS5O WE eal cee tected evoke insets 9| 6] 17] 7| 14] 24). 77
TAQ a Gr Ga | GAT ale rete |tscsell eceeell eceell ove taflestene 2). 6] 5] 21) 27; 2 63
PASS ei |G) PSO OM | byetellovctall eck ltevevel|ictetal atnts 5} 4) 5] 14] 18} 30). 76
1502) 565169] TSA seals crellissetalis tel tee talia ste 11; 4] 18} 9} 36) 45) 4). 127
150981168] S| LSOSe| egal soleil steel] cree] ticle | exeke 2} 1) 6 3] 39) 36; 4) 2 93
51S) 168] (Se PLSEO als ctl = ote | sell everel| ects 17| 13} 17} 15} 13] 23)...]. 98
asp ea EC Sa) Pao Sonl Pi 0%: Sa) 5) VR |e dio allono 1} 1] 8| 3] 50] 44) 6 3 Sea Lie

Tn

AN ANALYSIS OF THE EFFECT OF SELECTION. 57

TasLe 26.—INBRED Pius Series. 1002 Lins—Continued.

Parents, i 2 3 4 5 6 if 8
Genera-
tion and od Vic En as |
Grade. |
eae Cu lelalelalelalelalelalelajelalela|s
i ; a
Pic
F; TH2I9) | GG PASH he ccs |s ete |lctwces| a 2% LD Sait 6S} s0 e271 .| 87
1539 | 6 | 6 | 1403 |...]... svetal A) DLA) SZ S6i" i4. 88
1540 | 7 | 6 | 1402 |...]... SAAB Ser ool Lol wel) ls 31
1543)\| G)/h6: | 440 eee cie 3} 2] 11) 5) 25) 23) 3). 72
1546 | 6 | 7 | 1348 nistell aioe! hcl al|ckees TOOL Poles Dee hz.
1549 | 6 | 6 | 1375 16}...| 7] 10) 19) 26) 1).. 79
1556 | 6 | 6 | 1403 2} 2) 7| 3] 33) 26) 3] 4 80
1558 | 6 | 6 | 1383 1 Qh ese) 2EeLO) vA elie clever 38
F, TGS a Aa ar TIS Ua Uae | al yl fear [Sees one a Sl) 21 Sh od] 2a) Sass 32
EGST, | ct (UG LEOS Salle etell ssare'| esse a ctlereye 1 Gl) UY VS PA ilies. alle cell baer 37
RG 445 6) be |) PASS ey coclleetall ees |horere 16) 10) 2720) PAL OS ce odes 89
GTA |) lal Ge | Pk4 OS aE ee Srarei|'< <reillerste|lo evel] ouete 1 weet ie 1 br beae |eaeeal neh (a ae 28
TG ZOE ies | NOR | eaLers Ola eri vera | aset='|lvete\| laced fares [leretell ecevel tesases| aers ee) (ees ees lac 14
1680 | 7 | 6 | 1546 |. 1 Ailes Vis ee?) Vc 4 Re by AO DR eee | ee Pe 50
1681 | 7 | 6 | 1546 Th) 3) 24} 10} 16) 29) 221! Sa Ae aller 87
GO Z| at [ree |PALGOOWIL «cillcreney| ¢ crcl ecctelllo tates rereillsrelell eaetallenees Pet 9 13 sh 29
1694 | 7 | 6 | 1558 |. Dy Ly! 3h LO) LS) ZO ZO ce ec cilleeeilanats 81
WALZ) | TS |) W558) We es 1 AN AW LOWS Si LS] 12 | TA VS) cy ereiliceere llores levers 79
LSM Pe ca leds |) HOU Ce Me as Male | veto Sge'| ore tersifle ore] evace By) | | eal hoo 31
1734 | 6 | 6 | 1498 63) oe rr 0) 140) i a2 Ob De ete fas 75
F, 1788 | 7 | 6 | 1611 2S} OF) 25-20)" Lah lane 68
ES OBe | ela Oy NETO caratl or sted| sete: (rovevell ecehe'| eveyes ene cificys:ell lave Acoli te) | 9) fens eed (ool into 18
PSU Te live | LGO2 all al occa osc; s1| oete!| evate\] eceiel] ee; I Wi eA eas gfe 8 ee atic d 34
LSSON EGR ea |PLGS2 ers le ere |eveysil arate’ [lavenel| aves eihel ore Decors || peli | eA UA Sl persia ailtetas 33
1831 | 8 | 7 | 1692 DS] Si LE) TS SSA aioe =' [lave all lapere 89
1870 | 6 | 6 | 1731 Lj... .| 3] 2) 16) 18)}.% a al bes 41
F; 1912!| 6 | 7 | 1788 }. DH Shi 5] 3] Gf PE) POW I calto. ellee ciliveve 70
1998!! 6 | 7 | 1788 Petal) He|_ VB lore | Foye] aves «il kenene|| fener 12
1913 | 6 | 6 | 1788 1] 8} 3) 10} 2) 10) 8.. 42
1924!| 7 | 6 | 1788 |. DD 2 Al aa als 25
1999!) 76 | 1788 foie]. as 1 By A Tel Gh ST ALOW Medi| Seve sree |lerere 39
1939 | 6 | 6 | 1788 1PM a Va Val Ve et Ue ee 21
MOBS E56! SLU os rors crsrei| ler evsi|tereveitevveslletere Siete Ll ereust| feelers leceral fevers 25
1949 | 6 | 6 | 1831 |. 2| 34] 17) 21) 16) 15) 10).. 1 116
1974 | 7 | 6 | 1811 |. De Ai) 16) 39], 16) TQ eed ae ees (levee 62
1976 | 7 | 6 | 1830 |. I 3) Po) ae ed peer de aU le lien 35
1977 | 7 | 6 | 18380 |. 5| 17] 12} 18] 20] 18] 19].. 1 110
ZOOO! iG |G) PLS TO) | [eyed aces | orena|| lowers sce ei| eae eve ayate le oats 1G} es We hee 27
F, 2036 | 7 | 6 | 1939 |. 7 ess yf mate} ieee fa 2) (Vn Ue ee 45
2096 | 6 | 7 | 1977 siete ajay oct AID OuN EAC a lm 52
2101 | 6 | 6 | 1912 pV) ea eae =| Vs bat V2) a 53
2116 | 6 | 6 | 1945 Dy Shi 8] SIU STE Glia: le crolioxere 37
2117 | 6 | 6 | 1974 8| 5) 4] 6} 13) 15).. 1 52
2129 | 6 | 6 | 2000 Reel eus¥el lovee |lvate Sil Ali ever:|(eveteil teers 9
2130 | 6 | 6 | 1977 1) 9| 7] 12) OF 8 5). ; 51
2134 | 6 | 6 | 2000 Balls | levraye)| Ae di| LAL otetey|(evsyeltlerere 33
2147 | 7 | 6 | 2000 sells 24) 23) 2) iIj.. 50
Fi 2199 | 6 | 6 | 2096 |. 2) Li. .6) 12)32) 32) dh) Le. 87
2231 | 6 | 6 | 2129 |. eile LOW Lol chime hy. 29
2232 | 6 | 7 | 2117 Aly UWe26i SUL) Lee 64
2247 | 6 | 6 | 2134 |. We de COU 2al eee loa llarers 56
2308 | 6 | 7 | 2147 |. Bi] |e Nes ay i) ee 1} 33
Fy, 2338 | 6 | 7 | 2199 |. 1} 2) 34] 28) 8) 2| 2|...] 77
2354 | 7 | 7 | 2232 |. set, LE 20) <All) . < 36
2389 | 7 | 6 | 2247 |. Shy Ti Qs. 20 |

11912 and 1998, 1924 and 1999, represent two broods from the same parents.

58 AN ANALYSIS CF THE EFFECT OF SELECTION.

TaBLE 27.—INBRED Pius Series. 1002 Line. New Set.

Parents. 1 2 3 4 5 6 7 8
Genera- ———|
tion and | Grade. 4
out em elalelale|alelalela|elajelalela|s
ele y
2415 About F,
Massi|ifromi2389NlF eh) cule tac n| Lie S|) Gl 2420 "Shi saqy ane ie see 135
F, 2423 7|\6 2415 ofa} teat otel| fo cell foveal ravens cori Ly (Gl) sa SoIELO|e ceil presi er aeell rere:
2424 | 61/6 2415 iG fen) (oP (oval letra (ek) (eee fee WI | Or RG OTE ee) ae Te 78
F, 24421616 2423 pollsalicltoollecallaoc oh eral ae AN PLUG GB eres Aalders 20
2460 | 6 | 6 2423 Sollon||oo|aiollmalailogs Senleccl) “Sle tel 40ladl) oi Nh a 91
2461 | 6/6 2424 hell fove\| fetsi| felcell seetel| case Bafa |e fue fects) fetal] Pall ePale lis oe 80
2462 |5| 5 2424 erell eit | tales vail Inv cet los oie Sveteliteweillanee 4) 47) 37| 4)...]...]... 92
2472 | 7 | 6 2424 Fol1F ol [ecionol bcs ocalloa allncalleeca I TS 24 tee] Il et oe 8 78
2473 | 6/6 2424 gollo allo ollool lec lows DW osciincn|| ‘Giesolawh: S2h5 VEL 2 Sie 86
F, 2496 6 | 6 2442 So ord lanl Gal eed] lala foro coailesdlisds TOUS). a Zhe elle. 22
2503 | 6 | 7 2461 el} fotei| fauet| (asc [ts eucil evecei| teers fake cl al tOleeze| 23) tl a aes
2517 | 6 | 7 2460 azelltots|| (euailloesllleeretl ekous My) 2 2 S) SORSD) 2hieelicoel ase 87
2531 | 8 | 6 2460 syalllers)| late le fell erate le eit] avers AES A lee leo. 5 ASS | a ale 31
2547 | 7 | 7 2461 BES Sallotal| | 4 lass) foe 5| 4! 5} 46] 39) 3 1}. ..}104
2548 | 6 | 6 2472 da| lord) Fea (etal fs ool fosoc S|) “GASP 2727" Sa) eae ene 70
F, 2570 | 7 | 7 2503 eral ets)| evel ettall evetell fovereil erete X28 Tl S2ines: Deal never 79
F; 2654 | 6 | 6 2570 soiled) alleosl lees es: BB] Die 2/24 S6) A AD cai 73
F, 2758 6 | 6 2654 stall iatetl ferrell lene cual taketotl enels Pay | Veer) ieee Hes 6 We? b°-] Kava | |) EI fet 28
2767 | 7|6 2654 6-0) |Feal ato ool laa) Fansic lj...) 3] 3] 28) 24) 1). 1 61
2768 | 7|6 2654 Ac ollsalloallasaleicso| lors cece aL PAS PST ee RS eae rs 39
F, 2851 8 | 6 2767 eral otf dels Sail 'o3oil pore] etal aitogeidlcy oc] 0) NALIN Aca ee eee ak cd eee 41
2866 | 7 | 7 2768 Saf tami] loxel| loitellienetei| ice toil wt pseetlavCowell hy, -1eb1 Pave ell |cesedl | MB It cuct ot veteran oevel aeeret] MeL
Fy, 2917 6|6 2866 esalltevellleellagelterstelfeceislf, Bleeteda S| crete IMCoON TAI. Bale eiieens 79
|
TaBLeE 28.—CrossBrRED PLUs SERIES.
Genera- Mother. Father. 1 2 3 4 5 6 7 8
torn rear RE PPR |S po reeee Eee Al
culture S
No. Grade.| Culture. |Grade.} Culture. |9/|9/7)9/7] PI A) PI APIQP|AIQIAPIA
F, 937 7 Stock! 6 G02 |e cfaveisvatiexe te ely 21) 2h JO SiO) STS te alae eS:
F, 1040 6 937 6 O87 Oo elaclecloc|paterl “oem wl). Ol ose) wait 58
1041 6 937 6 C25 1 ai bee ec emesis) eel (| Pee mirc: Vege Ps} fle 5 A UB 97
1045 6 9261 6 1004! |..|..]..]..] 1] 2} 40) 38) 29] 30} 35) 22) 1)..]..]..]198
1067 6 937 6 937 : alte 5) 3) 16) 15] 17) 8]..]..]..]..] 64
F, 1074 6 1006! 6 Stock! |..|..)..)..1..]..| 26) 25) 25} 30) 34) S31) 2i..}. 172
1090 6 1041 1 LOSD. hoccdiecallls Alicia lecclbiorcll fe wteiflecote | eet eect Memo Me okra lead] eh eet Ul aa
1099 6 1041 6 1041 |..|..}..]..]..]..] 9} 4] 12] 15} 34! 30) 2) 1).. 107
1100 7 1045 6 1041, ji. .j. |. Jeet cle ot Si! 6] 12) 16) 40) 34p 2)" 3). 120
1101 6 1045 6 1045 |..)..)..]..].2] 2) 6) 10] 12) 19) 31) 28) 3)..]..]../111
1115 6 1041 6 LOADS ieee loin level ote terete cece ty OB erable oe tl te
1116 6 1045 6 OSD! *|]/57\|/ee0i))=) is ellloveifete|| LO Ole LS etapa a e2s tel eee Os
1144 6 1067 6 ROSA Gy 1] S705] ere level forall ouall etal] enete A LP) Sy SO) De ees
1145 uf 1041 6 DOB) eco leellieca| are tecall etal e s2ilterteo ls ace mens] tea) ed Ea feces) fave |p| lea

1Unselected, or from inbred plus series.
2This is probably the original extended mutant. Not included in totals.

AN ANALYSIS OF THE EFFECT OF SELECTION.

TABLE 28.—CrossBRED Pius Serres—Continued.

pay | 40
in|
|
|

|

Genera- Mother. Father. 1 2 3 4 5 6 7

tion and eee ores

eg Grade.} Culture.| Grade.| Culture.|9]7/9/F/9/7/ 91 7/AI\7!1 ela

F, 1129 6 1045 6 1074 |..}..]..]..]..] 1] 2! 2] 13) 14) 49) 52
1130 6 1074 6 1045 |. ail [or -| 3) 4) 11) 15) 25) 24) 1)..]..)..
1131 6 1074 7 1041 1} 14] 13) 25] 25]. .) 2
1146 7 1074 6 1074 wee[p |) 2 TG! 29) Qian.
1151 6 1072! 6 POSTS Alere|eellae lel erellea|i el | erol) A UTG LZ en Tele
1171 7 1099 7 10210) 9 ad] [I fea fo eval kb Gl oe ee eee 1] 22) 28) 6) 3
1187 7 1090 7 1100 1). Daa Pe
1188 ai 1101 ai 1100 1) 3) 8} 10) 48) 25) 1)..]..
1190 7 1101 @ 1090 |..|..]..]..].-].-] 1] 1) 15) 10} 60} 43) 1) 3)..
1196 7 1100 of LOOM We reileieillereliseiiersli eh |reel), all oe [pes 26)) L246 /eale
1197 6 1115 6 DOSIF Eee ore)|terall(elelline esas Ll! LO]ems|| 19) 1412 |eni
1204 7 1116 8 1090 5} 6] 17] 4) 40) 25) 3...

1227 6 1101 6 DULG) eles cilorei|iereifieei|inal? Li ell) $21) 663] 53) (2154

F, 1198 Us. 1101 6 DIST HER eeileci|i || Leal 721 18) LONe 8) 26) 23) .y.1 eal
1203 i 1130 7 1099 dicodiicodh 24s 1) 6) 4 1).
1253 7 1146 6 1131 8} 3) 9] 5] 22) 24) 4/1 ate
1254 7 1129 6 1115 1}. WB AS!) Odie sp cab otic aller
1262 6 1151 6 1144 1}...] 5] 2) 24) 21) 5)..].
1269 uf 1171 6 1129 3} 3) 5) 5} 20) 5 2) 2/..
1271 6 1190 7 1131 sreiffocsier|fexeres|| |g islll § Ol 2] rere ersi| ane
1284 7 1188 7 1171 2|...| 8] 8) 25) 23]..) 1
1285 a 1171 7 1190 2} 1} 5) 3) 20) 19) 3) 1
1293 7 1190 6 DTSUG jE s'|(sreifleieiltesi[ia s levelllte| noel) eel oo] 2413] baliiey.
1304 6 1151 7 TUS OR || Seal Ss kes ee) feed ce We ed Jee) etsy P| a FV
1324 ws 1204 7 AVA Wea fiassi|tsrof'soi| Leia) 25]) 2] Sita 29) (23) 2157
1325 7 1171 6 1227 3]...| 4] 6) 28) 20) 1) 1)..
1326 7 1171 6 1190 1) 1) 6) 3) 40) 18) 2| 4)..
1333 7 1227 6 LESS cl Saiioa|on)loolaallapellopailecal lors oak 4 CAX0 Maule
1345 7 1227 6 TL9OF Wereerelestioe|> sles) ei) eal Ol) adi Boles dL) Lik,
1353 is 1204 7 T2275 i \\eeeihore||tets|/oei{(ovel| Le Lh 72), Val S| SS8|- Sa! LET erly.
1305? |Not D’| 1197 8 LOSO! A erelfere||tsue]) L|'e0i|'|) Jl! (S|, Si GleLOy Olea erae.

Fy, 1334 8 1227 7 D2O3F 4 | erellleseifiate(evellletelaei|t Lean hy) ead yee pase eee
1346 7 1203 6 D208F Gl erelleceliee|tevedstelleralt af) co] LL Ossie 22s, (ed |bee
1351 7 1196 6 112187" | Sol lst foro| [eva faa) lc loca [eae add) se!) alloc alls 8
1356 8 1253 7 2 Cees teres ess | eel ers ak | veil etek (sees ale seal Ole Sipe] telat.
1357 7 1253 6 UZO5 5 1\/4.\]a-\[lerei|'= [eves ||. 4] TSG 1S) 20 aoa.
1359 7 1203 6 1204 Si[tereeiffore sift 20) ieee Ooliai| MGT EG IS. hse,
1360 u 1203 7 1WPIE lial |aallo olhao| ol laa] loca) eel ees! 4 ei Pe eal oS! Salle
1372 7 1254 6 A204 ere et=i|leieillsssi|'sonieo | Al) Gl DE TG|/ 5) Gly. eeerelin.
1373 uf 1196 7 1254 srte||le 1)...} 19} 17] 3) 3}..
1380? a 1262 8 LOGO) ecilfeic|creileveif ere |e 2]) 221 LOS] Oi Gi Slee este rltess
1425 7 1271 a USO eee aifie|oe|e | 24) (6) 19) 13! 39) 83)...
1426 7 1293 u DSOSs Piet. for) etm) vei|'=.c\|eisi|'sre.nifte eral 12 (eee || a ee Sle Zire,
1427 7 1285 7 L284 |\,1.)||-1-|s15] > 0's! 3]) 3] SiieB) 29) 16) 4) Ty.
1428 Z 1262 7 IEA 36) tte ba8| (or (el [ate deel loans tarcaal(do.ol pact. eed ned le ei
1429 7 1269 8 1293) |..}/-.]..,--[e-]--fe--| 2| 2! 8 29):27) 2) 1).
1458 7 1345 7 17423) |\ooloallon) |an| |aclignll eed lepallemel! cdlczalcy diay

F, 1457 iG 1334 U DBAS oF] [oysi| spel ovell oseif ercifistesiffarscei|iclerei|j 2 lhe) S| e alee.
1492 7 1334 cu. USSD Ee 4 fares fexni| fod} (ar || =i] evel lovevel| eke el | euay=i] terete | weed | a.m | te
1496 7 1359 7 1346 |..}..}..]..]..] 1] 13] 5] 24) 16] 48} 44) 7] 2)..
1497 7 1326 7 SEO! ||oallael lool laa aollaallaee| ual) edie Piel diya
1501 7 1356 6 TSSSO §| ese\lfo wilt |lersi|leil level (o'eraifletavel| eeare||ier=r| ale Lay ir DI ee,
1538 7 1356 i P3595 5 eicilfoc aif o7e\|(e0 =i] aheil[avel|'sisiafleravel| Ll eeere | LOG) Sieg
1541 a 1326 7 TSE Vig | lev | ebe\ffari| ose) |e llsus!| ecexeil levees lt eel eet | Ok ON Gly Sle Dia
1612 7 1428 ef 1426 |..]..]..]..].-]..] 2] 2) 6} 7] 41) 23) 4).

Fy, 1581 7 1457 7 UBYGH. Iter esl a's [ol lec iol lool Gioo| latalfo os] | LRH aU alls 2
1599 it 1492 8 1373 |..|..]..}..]..] 1] 7] 1) 15] 14! 39) 47/..] 3).
1709 8 1458 G Teoh 8 (Aci ca||6 allota| aia! [aun dial los 1)...| 10) 13) 3} 1).
1758 7 1612 8 LOSS ciflevel|ievel|/s eiflee|fereiliers «| eh|) Li ai 220 ay tea

1Unselected, or from inbred plus series.
2The o in these cultures also was the father of 1204. 1305 is not included in the totals.

oil Rod fou

60

Genera-
tion and
culture
No.

fs
F:
F,
F,

F,

F,
F,

Fs

Fy

920

922

1007
1008

1062
1063
1073
1082

1134
1135
1149

1258
1259
1260
1276
1307

1391
1415

1563
1565
1566
1577
1578

1677
1764
1799

1850
1862
1928
1930
1973

1995
2008
2018
2019
2037
2038
2039
2042
2043
2044
2045
2071
2072
2074
2140
2075
2120
2128

2165
2166
2170
2179
2181
2190
2205
2237
2257
2258
2261

AN ANALYSIS OF THE EFFECT OF SELECTION.

Taste 29.—INBRED Minus SErIzs.

Parents.

LPL LEDER AADEE PRPPEAPRAPREAPR ERROR PREERE PLO WONKNAEL PHL PEPER PRE PRE PE PP

OPRPNWWOW hE RE WWHOPRRPRAHR AHL EPR PERE RWPR WROWP TPR WNWWN PE PROP FWP POPE PP PP

Grade.| Cyl-
2 || ture

900
900

920
922

1007
1007
1007
1007

1062
1062
1063

1134
1135
1149
1149
1134

1259
1259

1391
1391
1391
1391
1391

1565
1578
1578

1677
1677
1799
1764
1764

1850
1850
1850
1850
1930
1928
1928
1850
1862
1862
1862
1930
1930
1928
1928
1862
1930
1930

2037
2037
2018
2071
2075
2044
2038
2071
2120
2128
2037

wHoDH:
4 _
©

_ bo eho
OO AWN O HAO AHwW

bo
wo

Ll lll cell seal aoe aed me
NOrFCONPN NH Or wS

10

i Hee Re od
POR ABDOrRN PHO WNP

J
ae

i!

_
DOE EOWNODOMRD PRONWNOODHNOD

900 Line.

a

_

i

KBNWNWOPRONOR TRF ONOUMREAAMNNNTAANOH NWDWNH HRW ops:

i

ee

=" .
Be eR wR ON OWI:

-_ .
KON ONROP Oo PR:

| a
40
Q
40
Q,

i

=
PPR WRN OW Wr
i

Wa w:

ow vbeNwww :

i

—

Genera- Parents. 1 2 3 4 5 6 7
tion and Gude wae a
culture |OTAade-| Cul- o~4
No. O1¢'| ture: SFSU Sao NOR Sn cHIES: Lice Shree: let ou a
F, 884 | 4] 4 868 ay 16 138]. 118 111). 74
F, 898 | 4 | 2 SSA Re |e cl thes [fet eh ay 156)... (228 194)... .|. . |109
F, 923 | 4/4 898 2} 2) 2) 32] 31; 10) 11) 6] 4). 100
935 | 4 | 4 898 i eo era 10) 39} 22) 5) 5] 2) 1; 93
936 | 4 | 4 tty 1S Balls colle col ape 1 aU att gal 1 ae 5
Ky 1047 | 2 | 2 935 1} 3] 2) 14) 24) 18) 3] 2) 2D) d.. 68
F; PANE AS) LOT. | leer ellen 8] 3}. 4; 2) 2). 19
1132 | 4 | 3 | 1047 1 1)' 3) 34; 10; 6) 8 I 4I).. 65
F; 1257 | 4 | 4 | 1117 Ol) Sl A St) Le Dea ierel|le mei 22
1Sexes not separated in this count.
TaBLe 31.—CrossBrReD MINUs SERIES.
Genera- Mother. Father. 1 2 3 4 5 6 8
tion and | 3
culture I
No. Grade.| Culture. |Grade.} Culture.| QI} PIA PIA] P| AI PIATI PIA oh ied
F, 1039 4 1920 4 1936) foal (ocl| Lisalesiios| OLl L621 bile Sil.
1069 4 1935 4 1949 |, 2). |c of. | 21 28) LL) 10} 14 8) 66
1070 4 1935 4 1G AD A aes [eat il iere|| e2oq 2Ol 2k) Dao 6k 3
F, 1087 4 1039 4 1039 |..\..]..) 2). .| 4] 59}, 438] 10) 15) 2) 4)...
1093 4 1039 2 1039 4| 35) 32) 9] 11) 2) 4)...
1094 4 1039 3 LO39/ Gilsal salle a ral St GI) ail) SAREE Dee
1125 4 1039 2 10472, | ..<]...}|. «|| -2]/. .|12}:40] 26] 9] 6f) :2) Gi...
1136 4 1069 4 AOGSY Wx lealie cece!) LIMASSWe2VT) Sl Lae a Le
1140 4 1073! 3 1047: }..|..|..| 7|..|19] 42) 26) 9) 9) 9] 2)..
1155 4 1070 4 1073! 1; 10) 7| 14; 12) 8} 1
1156 4 1069 4 1070 2) 13) 12) 4) 4) 2) 5)...
1159 4 1070 3 NOS MEAs sls aleeleaieelaeell vain cde collects lis.
F, 1168 4 1082" 4 LO9S) Blerallcterel's. e|iarleetieLe 13 LO WO Ol Sie.
1169 4 1069 3 1O8E Nessa) Da Slab SLL! VS NEKO] + 2
1184 4 1093 3 MOBS: Ws celcelteallece aha ble a) cSt” SU ST Slee
1194 3 1070 3 TO94. Wessel eciiecfier ene 229], LA) Li TSS 18) LO}.
1199 4 1087 3 JOOS Me cale delenit eh 2a ZO LE) LONA ia) aie
1209 4 1125 3 IQ5) Wesiecle cll ol) Likeiaee| 19) 10) wisi aie.
1210 4 1136 3 1093 1; 10} 9] 12) 6) 16] 6)..
1223 4 1125 2 1087 Hi Sl) 7 1S Sl Si.
1224 4 1087 3 PADS leet fesel orl lee! 2S ay OUT OT 2).
1225 4 1136 3 LOST Wishes fod) Netter (6h Dan 2) cal eS...
1231 4 1125 3 WI4O. alec icc|ecalecakel 2ule (Glo estse|)) a
1236 4 1140 2 PIS Ae seelealcalc Heinkel) Om eG mooie odie.
1241 4 1140 4 ATO SAPS Merl eral k lead | Les Ol Lae: ‘Gls
1242 4 1155 2 VIZOY jy. ye ies) Ds 4 25), 16), TE) 4 3). 6...
1243 3 1136 2 TAZO Ne alnalleatcet este c ell Shea SETI Sls
1268 4 1136 3 1125 vefeefeefecfeefecfees 5h Si) TSP 29} Gh.

AN ANALYSIS OF THE EFFECT OF

Tasie 30.—InsreD Minus Series. 868 LINE.

SELECTION.

6

1Unselected, or from inbred minus series.

1

62

TaBLE 31.—Crossprep Minus Smrtes—Continued.

Genera-

tion and

culture
No.

F, 1256

1273
1274
1292
1300
1301
1316
1317
1321
1371
1377
1393
1395
1396
1397
1410
1411
1412
1433

F, 1413
1414
1434
1441
1466
1468
1469
1470
1475
1476
1477
1488
1490
1523
1525
1526
1531
1532
1545
1568
1570
1573

F, 1666
1668
1669
1687
1706
1738
1741
1759
1779

F,) 1878
1879
1881
1882
1892
1917
1943

F,, 2015
2040
2051
2076
2110

F 22189
1 9954
2272

Mother.

1168
1125
1168
1199
1194
1169
1194
1209
1194
1194
1243
1225
1241
1242
1236
1242
1241
1210
1243

1274
1292
1274
1301
1317
1292
1292
1274
1316
1273
1316
1301
1321
1321
1377
1301
1395
1393
1393
1395
1412

1433

1488
1531
1525
1526
1525
1523
1573
1545
1573

1666
1759
1706
1666
1759
1741
1779

1878
1943
1892
1943
1943

2051
2110
2110

CO FEEL EE PEP EE LE OPA EEE AREA PER PRAR ERROR RR ORR ROR ERED ll ee a

Grade.} Culture.

Father.

Grade. | culture.

1 2 3

1140
1168
1140
1168
1169
1168
1155
1169
1199
1194
1210
1210
1243
1241
1242
1242
1242
1224
1268

1223
1236
1274
1292
1317
1273
1292
1273
1316
1321
1321
1273
1292
1316
1371
1377
1301
1395
1377
1395
1412
1411

1488
1523
1531
1525
1570
1570
1568
1568
1573

1706
1706
1741
1741
1741
1759
1779

1881
1943
1882
1943
1943

2015
2110
2110

WWW NWNWNH PWWWWHWW WWWWWHWWWR WWWWWWWHWHWHWWHWhORWR WOO PRPOWHO RE RP ROO RR PR RDO OO

Mm.

bbe ce es

boop:

wo!

Loaenwny:

Noh NY: Ow: © m:. woh:

RPWNONWWNIRN ON OH

ier
Qrom:

two:

= z
© wwmwe.-

_

4

5

8) 9} 21) 16

8] 13
7 12

i
wo
aonn

»
i"

_
wo
_

_
=
. ee
AW: OP ROOWMN PEON NNEWOORhWO

ed
Re NWDWR Be eo oh IW O RH wWOW WO

ale] ale
a2) cr7|).|) le:
37) Ed Nal alloc la

OW AH ANWwWwnwwo

i .
BNO NWwWNN NNNe-

6 7

| &

al.

NONFPNRFPwWOOOH Yep

_

_ 5
SCOPRWWRONWAR WHE ROH: NWR ORO

_

VONeNOMAe oa:

CrRNW ONNWH eH ONaOsA
PY oy: bP ROR

_
wo:
PAS

Nooo:
mh ee:

wi:

tee

Oe
Ww

AN ANALYSIS OF THE EFFECT OF SELECTION. 63

TasLe 32.—Speck Minus LIne.

Parents. 1 2 3 4 5 6 7 8
ee ———— ————— eee ee
gongnd Grade. ra
ON | CP NSISISISI SIA SIE S| SS |elalelay 3

5 g rot a

rie pene. 1168
F, 133i{| 4 sae ety tere alls lease eal 30l034 liz ar7|) -8|P Glee clea eval Lee
F, 1465/4] 4 1331 Palacleclasieaieal22! 18) 1Oleon tl) 6 .| 79
1487/4] 4 1331 ..[.-|-.]+-].-|--| 28] 15] 12] 14] 10] 15]..] 1]..}..1 95
1507 | 4] 3 1331 1 | Sal pale a BS INST ST So]! SSit Ze. ol Relies
F, 1594] 4] 4 1465 ‘|..|..]..] 2}../11] 56] 51) 4) 2) 1) 1 .|128
1595 |6|] 4 1465 so lool loclloaion| ci iexl| Dea deeci cat 63
1617| 4] 4 LAS 7: © aellya tise a ecs|eya|e2|he0ln10| 3] etl) all) 56
1640| 4] 4 1465 ‘|..|..|..|..] 1] 2] 36] 29] 10) 10] 6] 1 89
1728/4] 4 T5OZ elec |ealleclelac|) 19! 7] alee!) zi) LI. a|eateal\ 59
F,1766|}4| 4 1595 .| 6] 45] 48] 4) 3] 2} 1)..]..]..]..|109
1784/4] 3 1595 ‘Pal irg || 10 Sse .| 26
1786 |4| 3 1595 A oil isl PSEA salle 26
1820/4] 4 1617 .| 6| 37] 30} 4] 2}. 79
1841} 4| 4 1640 5a 2a OR eel a 65
1861/4] 4 1640 |... .]..] 2} 24] 23} 12] 10] 1 72
F, 1906/4] 4 1786 Sel eel tel ol lal eee oe) al a 47
19071} 4] 3 1766 Al; TA) O3|aaal/ soles 43
1996'| 4| 3 TZEG eho |e | alee nelle 27 [e258 |. 58
1955 | 4] 3 1766 Weclesiealed |e. le4|ee4ieis|| Sis a 51
1978/4] 3 T7840 alesse (aaleal se lenleseleiels vaimeesieme (td .| 50
1986 | 4] 4 1820 AS}) SG psi Peal ney ae 27
2009/4] 3 1861 ~ Bae pr4 |5 | ll ee ee 31
F, 2088 | 4] 4 195500 Nee) ecler idee | 5 (184 e24i) oll 65
2093 |4| 4 TOOG I Siler [eres lee el peti fade oles 26
DT Ta|aalns 1955 ey ee fegel (Pal ha}) xed Sa] UT le 47
2197 | 4 2 1955 Be ee ees alae at Ne S| All Sa aT 31
F, 2182] 4] 3 2088 5A lel eval eel lal Hal) et) eel Mendiseallsee FAA Wallac ee
2196 |4| 4 2093 Salo rel eel ete) | 2 eel lel le el sce PAE Aba
2233} 4| 3 DIOTE Eales} alla: 10149|p43 |u| eS |ase lon sal beal esl ebay
Fy 2348} 4] 2 Ps deel ef a fae (ae (Cc mes ees | | Ped beet
NEW SET.
2414 Mass. About F2 sve] Lieve | Mien PLS PLS]! SirsiZ)\ al 44
from 2348

F, 2431/4] 4 2414 Ey) eae Mal 7
2432/4] 1 2414 27 s|ed 14
F, 2486 | 4 4 2431 1} 5] 16) 7 5) 2 36
F, 2545 4 4 2486 1} 10) 16) 3}.. 1 .| 32
3546/4) 4 2486 AL ECSU 5 eelloaalgeral|aan joel belloel evel ee
o549 | 4) 4 2486 6 [P24] 70] Sie) eaietls ea) aaa
2572 | 47| 74 2486 sailors epeiffereiiete)| PIE S|, I S|lus 1 11
F, 2598/4] 3 O545) 7 |eclecte-|\'1|- |) 6|p20||.22|) 4). 53
49601 |4| 3 2546 ol eel ee) onl el eae RC) [REN 1 34
2603 | + 3 2549 =e} fors| ete | aL ots)|) teeat| LO!) Vee 21
2606 | 4 4 2545 A eillere\lferal|leraillake\lfers!| hekOl LOU 2lpaed 18
2631/4| 3 2549 ae AVE SIAN El) ibe 37
F; 2663/4] 2 26087 - —|h.|\ Lio.) 1Ke le 2) 3l)) Tele 16
F, 2760/3] 1 2663 SAllgeliseltealloellep|| eel au Alls 7
F, 2860| 4] 4 PO NCE cS Bsellballae|| te)| ead Sllaal ee allege 7

1First and second broods from same pair.
2Two males and two females; the same flies as the parents of 2445 and 2446.

64

AN ANALYSIS OF THE EFFECT OF SELECTION.

TaBLE 33.—Cross or INBRED Pius LINEs.

Genera-

tion and

culture

No.

F, 1941 bes

F, 2053 7
2054 3 Gike
2082 6 5 | 1941 nes fe) |S He at) Pee ey fenta) tevo ci 33
2083 6 6 | 1941 Sirah opel) Lol Gl ecsrclles ciblecneiaters 28
2104 6 6 | 1941 BLD) SO) LALO} 20) eres) ee] far eral orene 81
2122 5 6 | 1941 Die Ta ea NS rs eesti, Seciloveretbepets 35

PLUS SELECTED SERIES.

F, 2160 6 8 | 2053 aval al. igarilbe< 4) 9} 16)...]. 2 32
2161 6 6 | 2053 1}. SFahai| (ekerel ete isl| oes ZN) Gil Peal) 2h) RZ retains 20
2162 6 6 | 2053 Dal 2) ES EE 2 ae elas a\ile aalllapwee 79
2164 6 6 | 2054 aU i: Vee Vii = a (ics 2 | Vs UR Tr 76
2177 6 6 | 2053 Die erelleod| al Ol ervellts 1}; 1) 43
2185 6 6 | 2083 Ol 2) TAMILS SHE Seale vsvell nara 44
2229 6 5) STO rei level wai evellleveveil ec stei| nites lIhare ei] ashe Scafell|, oreSt! CA) ecole erst araea 18
2249 6 6 | 2122 3] 7] 6] 20] 25] 1j.. 62

F, 2280 6 el Caleb alls! |na| Real ion |Goul lb pol locadllana 1} 8] 15} 2| 2 28
2282 6 Ye | PAGO MIE SSS IIE Siig alae! loro] lo eral aco loo Be) al aeellags|lsas 10
2287 6 6 | 2162 2 OHM tbs alloca! las 40
2298 6 (OAC Bll55|loGl bol aac] lao al lgeo|loan| dou 3) 25) 031) ea Gi) ot 40
2301 7 2a Salis ASS lal leral oallgo olla ool local lao) las 4 CAV eel laa lecroltooe 18
2314 6 G38 APA e Nae clSalle allie |loato oheei(te eee dl elt wo lie ek, eorel|fetrens 18
2317 6 8 | 2177 2]. ey ASRS 2) PSP eae ae 44
2332 7 CF PPP. al lS clio teoo| lariol loool sal laral load 21] 14; 9} 10} 1) 2| 57
2355 7 eee Oy Ne ollBe|laai|nallaod| ac AO yT iil) PA Rares 15

MINUS SELECTED SERIES.

F, 2178 4 5 | 2054 al e-crellc ste Qs Dea WS G22 a eelererstbeare 51
2197 5 5 | 2053 Lie Gl) tS ieSly wie vorieners 20
2198 4 5 | 2054 ares ee Sei, (Glue ceal lh eee| ee (eee meee 13
2212 4 5 | 2083 1}. 3] 2) 12) 13)... all sielinete 31
2250 4 4 | 2122 A SS TA OPA GEG eal ever: lee =| (asetell ater 69
2251 4 3 | 2104 ml Ce) else Dl carol overe 21
2262 4 4 | 2083 | edi] eek rel) ek etait raps 15
2271 4 3 | 2104 wale 4, 4) 2).. iL} 2

F, 2329 5 5 | 2212 Meal call ee Sl eGl Llc cillerers 16
2385 4 By E2250 eral. MES Shale AD] savel| erate 17

5 ...| 1944

F, 2069 MG ae) 6 teed Bolla 2} M9) 8) LORD 2 25" Si Pak Sh Sees 68

F, 2172 5 5 | 2069 el VA Lgl eat Sica) oll) TUE saierre 124
2173 7 7 | 2069 TE BPA) eal) WE SYA GE aN eR al lealleoc lll
2244 4 4 | 2069 Si Fl) SIS 020 ee raliccava eras iene 73

F, 2279 7 6 | 2173 sore Le Ol) acd|) Sl ese 43
2284 5 4 | 2172 4, 3) 5) 37} 39] 4) 4). 2.300. 96
2285 6 6 | 2172 PAteer AP PAIR es Gi! anil Pdloallbad 88
2330 4 4 | 2172 Halos alec iezoleeOlmiat eal. 2) 58
2331 4 4 | 2172 Tl) (Gl Gl 262-28) 40) S| El. coe 115
2403 4 4 | 2244 eel) Sa 24) FEY Sal eae aos] aco 33

F, 2409 7 © | 2279) | rls. silts Ballo ie 12} 4). 2| 1 21

F 1602 ae lpr fata 1 8| 7| 13 28 25 | 82

, 1602); 6 | qai9fl-"|-- fe eiatallecayellecseel ee

F, 1751 6 6: i) 1602) |.) ... 1 Bl Dl || OAL Gi llc orel|torstel| lscevellieters 44
1774 6 6 | 1602 1 is ie 5 TRS 3 fk RT 2 HRS | J 1 27
1791 6 COO a ete creslieci|lenaeall tered lecexsiekere 3) ek SI by J a | 31

AN ANALYSIS OF THE EFFECT OF SELECTION. 65

TaBLE 34.—Cross, Pius Line X Minus LIne.

G Parents.
eS | i 2 3 4 5 6 7 8 ’
tion and | Grade. 4
culture Cul- s
No. Q/ A] tre; OPI Q| FI PIPPI VPI PI VISTI PI Al/el|alela| &
6 |...| 2866
F, 2939{| © 4 aa Bed Bee) eee acre ference eA eres eS Ola ko OL es ole mabe
4 |...| 2860
2950{) * ‘ ae sree eee ae Pee ee ole Ve elect gol g8. 222r ce Mead tg
Fy 2999 Bl nGOalP2O39 ieee. « Bscileelssh se col ee eco Pa FOW Ol Bo. ol Beet at
3004 | 5 | 5 | 2939 |.../... Tae rai 2| 20} 261) £6loL2| TE. Gl -Blic close. > LO’
3008 | 4 | 6 | 2939 }...]... Fea) Ol) LP 4 Si) 26) 28) 2a 37]! WO...) cet a .../185
F, 3062 GRO MRSOOS le se||etesllistesilistes|(eleci [ferrell] Lieea|ie ei 21) 28) 201 Bil a] sale 70)
BUGSE Wea pet POOF. Hecate < [ecraistere || | ay A DGD SS FS]. cil clk ob 2 See 68
Raa kl the Oe Prerer mere rate] cleo elerts tl Mey RA DOteMS! WSN IBh oot te Ls ...| 86
SLOT | P46 S)1 |e OO8 |e istessilictsgsi|iaferel|lacorsii eal) 24) LALO S| A PO | Es sien 84
BOGOR on Pom CSO al yeieecrellccc ol sferctiiccstnedicaalteeaia OL. ei eelleca Qiyccullcnhs wes || Ok
S00Gs | (GCE S004 s | Sonimeelctlicsalleuelccdals oi 00t: 4IPSBI 231) 2Ol Tih 72)... el So
SETS OO) INOe OOS aerate | rots lierarail iret arete|| lfc ecll eh UIT eH ete os wrerd| 24
3077 | 4 | 2 | 3004 1) 3) 16) 25) 4) 3] 2) 1) 55
SOTST Gs MEME SOOS ol ere rallies) ate.) efesaillsiei<il stern ie cose lore <4 Ol) e420] Sol) LD] Slkvaile.a || a&
SOT9E 4a ESN LOOUSa| cee iisclecciiineleeeie 9) AUN 2ORSh Sar Ll ie ee
SOSST Sm | PSM ESOOL ler si faye ail seevalllokicl| cpece'|ieres (fecal a oily Al mPa) V7) I ek ...| 48
BOSSE SE [ose s | BOOS ac yefeiltevs [laPareilloca'|lexeresetacit aa eg LOS] Ol] PO oe, Sarat dia
3090 | 6 | 6 | 3008 cafe .S| Ole on LO 20) 23) A ee cle Sed
3096 | 5 | 5 | 3008 Gl DL] LO] 12) 241) 8 be ecl|e.e Set ecAl
3111 | 6 | 6 | 3008 2 2|e SS TA Se Sellers clfteres Sel oe
3112 | 5 | 5 | 3008 PAI Gl LOST Ole salve olleca. vee LLO
TaBLe 35.—REVERSED SELECTION, Minus To Puws.
Parents.
eae Inbred 1 2 3 a 5 6 7 8
jon and | gens. |Grade. =
culture | before Curls | Eres ee ee AS ee -
No. | reversal.| 9 | ~| *¥* |olglolalolalolalelalelelelalelal é
900. Inbred Minus Line.
F, 1086 2 Sh G HOOT Alcalliesils cher ternary 10} 13] 16] 13) 11) 5}..]..]..]..) 68
F, 1175 6) GS LOSS) Sei ealh llere|sverifievers Zed ||, Si a 26) 1S) ou eat ad
F, 1288 GF GHETTO ec slevel S alle cies) LL) SA TS ra SS) ih a ee. 66
1289 GEIS i MZ Sul rel cvelltere eral seers fever iin cel) clk Ole At eDOle velit Rieltieq tera eae
868. Inbred Minus Line.

F, 1066 3 6| 5 OSS Steal croillsrell sve ie! sve 7| 23) 16) 21] 22) 13) 10)..)..). .}..{112
F; 1142 Be GSP OCS eal sraflese [fells i0:0 3} 13) 21] 12) 8) 18) 4)...)..). a.) 74
1143 O46" | 1066). ace le el ss 2) SiS) LORS! AGE Sly teal. ate) OO
1157 CEG TOE: Paes ebs |) Docc) Ly ON a 20) 20) 29) a2) eta. TOL
Speck Minus Line.

105 1627 2 Gr) Go) 2607 Wee te hse cliss-) GO| 48) 252! 9)" 7) -. -{161
EF 1783 SoG eLG2 7A eles cscs ell Ll eSHea SSITO| 34) Cai. 40
4 1843 GHIGP LG ZT alte cits [lee lisecl]l) so] LOL Male Ole ead: oot i 51
F, 1893 GHMGnetZss se alacletlee cli die [TOW Ns! oTieesly Til. 21

Cultures in brackets are first and second broods from same pair.

66 TasLe 36.—REVERSED SeLEcTION, PLus To MINus. f
864. Inbred Line.

Parents
Genera- | Inbred 2
tion and| gens. aa 1 2 3 4 5 6 7 8 Ae
culture | before Ce —— ——— —— sn 2
No. reversal.| 9 | | ture. |O/P/Q|F) 9/1 F/I PIP| QI FI P|FI/VWA/ QI A| &
Fu 1940 10 ANS L763, [ele al eal eee eter oe gehen |S | ee ea ee (33
Fie 2089 sys aks AVS) |LOSS ih aillcvcllteelllate oi exer Voie |\ekesell Set ON) GH ANE al exeilievet| 20
2125 ANS) | 1940) |levellis-eerel|) Wl /csee| el, 8] eS] S|) Ae er rte pall)
Fig 2269 PA NRA Ve DESH cll aires | foneil devas ienane 2|...| 12| 8) 22) 18) 2) 1). .) 2) 62
1002. Inbred Line.
F,, 1522 4 AND | Sqou| real ere | ees] hs] /-tei|) DI) eal) S|! Lol sol eel. 62
F, 1686 4| 4 | 1522 - 2} 10] 13) 5) 5) 4) 7|.. 46
F, 1816 tee 4 | 4] 1686 |..]..|..] 1]...] 7] 29) 17) 5) 4) 4) 1)... 68
F, 1958 shots As eSil ih 816) Rel elle rei| shell tees etocci| oti. ork! Rl! AT eal] eel 23
F, 1908 6 ASU | TSA ahead] score ecoest] ol] 92] tegen feed 12
1997! 6 AS" MLZSE | |(Falie sl icr| ol) OL RA PES eats | Sirol en a. 37
1909 6 AD | es | Pde SA || Sy] bese fave toned] fates 5} 17] 18] 13) 10) 7] 6).. 76
New

1Two broods from the same parents.

Tas_e 37.—Tests ror Mopiryine Factors.!
900. Inbred Minus Line.

hoe Tae Parents. Ofeniias Nolet eal ee 5 Se cea aE
culture § |————;—_ characters. |_———|———_|——— 5
No. | Soma. | Stock. | Culture. WA QAI PIF PI A/ P| A/a] &
1737 és 900 VUNG aaa sac Me Sle neelost ele eel La of Gl soley 56
p Sp By phy al bev cctay sp ater snot cote es call czei| lameh feral Peres | es | Cea (> ee | le Penea| fae Det eeteal I see lene tocol eset] opera

1937 { Sp Sp Sar lackey TARE Sn Tl) a) 88) LON 6) 54 35
ALN tere 1737 SD oeebieuteee 1} 4/10) 3) 3) 4) 1 26

1970 Sp Sp ae oa Reet: 5:20), 6l) Si) 4) 41
6 sctc 1737 Spee sere A Sil FS] 2h Sp dl 26

864. Inbred Plus Line.

Sp Sp HEA ell ae ooo eet Ont lac tal Onl leoltoal (Gan lenis acalloeal|doallssalles efter

BEE 6 | seal) azese | SE SEO Ves Va} al 2} 3} aa} as} 10}. |.) 45
2023 { Sp Sp si igs Fe ae Ale4i) Si Sal 7), Gl) “Giaesiee 35
6 Piss 1921 Bp dick Ste crows alle 6) 14) 2) 2) Dy aie. 26

2024 { Sp Sp ae aes Pay ety 1). A UGieat| Sit Glpaale 32
6 Byalcke 1921 I=) 0) a NR eR ST OU) 3 fomest Poaek Sa He HY oa) ee a 23

2065 { Sp Sp aoe age? Brafcone mils PA) a $81)" Gy silos 15
6 eisters 1921 SDsecctisraesee Bello PA PA Seal faeol loo 6

2175 { Sp Sp OG jecae Hetes cate Reel Pelt eal enamel eielelass 45
5 2023 SDarcn kena MAT) Slike) cell sere 32

20912 { 6 1921 ee Lisi ieteneke (2) 0 = vel t=] pk) fee be 30
Sp Sp b REESE Rpdasismn aces 1 Ale 4) (2), 2) Slirevilins 16

21432 { 6 5 1921 INOTSDie ss «jcieysis eT Aly PG) LS ae 20
Sp Sp ahs Diasec ere Pe e2 eat areile Fall ene (Pama T Achy tec Seek Reade roe oe 18

Not-sp not-ro.|..]..|..J]..|..|..| 4) 2] 1) 4) 2] 3).. 16

2245 { 6 Seino 2065 Ie foro Khaw al leralhaellaollosl te llmolle tamed Zapf ai 2Als6 19
az Spro| 1331 2127 Sep cRe loalsallene ealselbilp cia eiisnoll Zilosal) lac 13
Tyee eee el fete lene tecl Peal (eral fe!4 fee te) easier di ac Ab Tlic 27

1JIn tables 37 and 38 the upper row in the parent columns refers to the mother of the culture in
question; the lower row to the father.
29091 and 2143 are two broods from the same parents.

AN ANALYSIS OF THE EFFECT OF SELECTION. 67

TasLe 38.—Tessts ror Mopriryina Factors.
864. Inbred Plus Line.

Sees Parents. Offspring) 1 | 2] 3 | 4 | 5 6 |7|\4q
tion and quae 2
culture |= |————_—__—_- ea lar al oe al ae She
No. Soma.| Stock. | Culture. QP PIA VIA) PIAL PIS] QI APIQ|A
So ile Sep cetera Neraeerse eR || ha alla ea] 10] al) 37
1946 { 6 |x See: eNOS | Looe... 5a] Se 2) DV Vs a
6) lanean lienaden |fiNotepeleclseoledteelusiias|i13| ell cz) el) al 45
2030 { Spalt Guy pesas. LiiSosesks ~ lo}. -} 2) 2] 2] 15] 14) 2} a} a} a) |] 38
Sp Sp Suet INGY ES Neliga h-oleeltocllociloglieec|la el -<jlame 410k) [ae 17
2032 { 5a ee TOSS Gee INCI leclee leat w2lkez|) ol .Slh al) DieelPas
Sp Sp cee INOt-BD alee alevalise|(eccHtetel|iarere | aeLead LES IS\te 9
aus { SE hehe | PASO MSDS ss: eee c\enlclct@caleec eMie aisanls ares ieall ta
AS || seehlal| Ones, lh Ohana ..{.-[.-[.-1.-{ 7] 28] 16] 10} 15] 6] 2|..|..] 84
2086. { Fea (BETS (es da en S| | fs =
5 cee eoRenlliNotsen alli aiselelscleeliealie Sibesll al) cal os) gellcclita
eae Were 1380 | 2088 NWSpeecealmcfe(eo|.le--.| 231 9! a) 1) al alah [a7
i { 5 |.... | 2086 |f{Not-sp.|..|..]..|..|.-| 1) 13] 9} 8] 6...| 2l..|..| 39
z Sp se| 1331 | 2127 |\Sp..... aleecleclec|| Healy zieesh tialk cle Meliss
sare { & \-2.5. || 9246 | |fNot-sp.||..|.-loc}--[ecfe<{e2a) 11] il 5] 3]. 3lec|..|/ 40
Spisellelgai! le 2933) Spies sleclecleclecleclsclhamitezieeell alieal) Siecle Mo
an { 4 |.... | 2246 pNeeza abel: Va) zie) Tle cele 20
Sp se] 1331 | 2233 |\Sp..... Oe ee eal ala eal Wal eG) eal ea ee \..| 17
Spi4|.... | 2246 | Sp..... Sl eaecloeleeleatlimes| S|) 21) 6] vaall ialcalie itis
2376 ee 1331 | 2233 | ....... A) ih | Fie aR A eel
sae jie bess I 22464 I Spica. Pel lal ale )tgl) walliselt 7|') 20 4/9216 |/40,
Sp se | 1331 PPR SY TNE Gece cr |oo| lox | lena eet sxe [eel = ake oll aterailicx ons |faitebet] (a cherie le elle cane
Crossbred Plus Line
res (er sa ea een Oe 3 fat es ess ee a
Sp Sp Eerie Not-sp. Bales fhe ai ee 16
2078 { .... | 1948 eee 2 1} 3] 4. 7
; Sp Spy lidasceen eee a avers 5} 7] 5] 13] 5). 35
2141 .... | 1948 |{Sp 1) 10/ 5] 5] 3] 2 al. 28
Crossbred Minus Line.
8 rey ba 2 cel ee ee el fel ape (Ey Lt a J 1} 2} 1) 3] 3 10
aa { Bene sant ise eee [ce Ales | Weohees yay | ed a ee
p 5 2201 |{Not-sp 1] -2|...| 11] 2| 5] 6 27
2382 Ateies 1331 | 2182 |\Sp. 3} 2} 2] al al. 1
PSO a age a zea halen Pol sles |e”
92959 { Sp Sp Hotere Not-sp Pllepalle ee cH ay ]) cae 23
2 4 2131 |\Sp... 2} 6| 3| 7 2 ai..|..| ot
5 2259 |{Not-sp ray ll 0) eat 20
2378 { Spit Sp: | oS-a) [\Sp. 9} 2| 3} 7] 2l...1..|..| 23
Sp 5 2259 |{Not-ro 2| 12) 8| 3] 3| 2] 4]..)..| 31
ake {tes 1331 | 2233 |\Ro 2} 13] 7]...| 4}...| 3/..|..] 29
2395 { 5 2259 Not-sp 6|- *Sy ey) Ike pia 13
Spro | 1331 | 2233 |\Sp.....]..|.. ll eten| | |! allel Gail |. | os
2396 { 5 N. 2259 |{Not-sp Aly 25 lees ||. Si: Bios 18
Sp ro | 1331 2233 Spoece:\|. alae SLOW 31)! <Bline Lie 20
2397 { et Sees 2259 fe 22), 4 er AES. 20
Sp ro | 1331 2233 Sp 1 13} 10) 3). Bier 28

1sp se ro. 2ro. 3 Includes one O male.

68

Tasie 38.—Tests ror Mopiryinc Facrors—Continued.
1002. Inbred Plus Line.

Genera-

tion and

culture
No.
2025 o028 { Sp if
2153 { Bee
2150 { a
2333 { Bees
2433 { 2 ie ro
2471 { epee
2481 { ae
2488 { Bie
2516 en
2436 Bi
2480 BP
2475} &
a5ist { x
2476 an
2519 a
2607 { my
2669 { =
2698 a
2699 aR
gria{| 8P
2682 26
2665 a
o7sor { oy os
2803? { ee
2633 {| SP
2690 { eye
e704 {| SP
2811 { anes

12475 and 2518 are two broods from same parents.

Parents.

1002
1331
1331
1331
1331
1002
1331
1331
ee
1331
1331
1331
1002

1331

Soma. | Stock. | Culture.

1924
1906
2009
2025
2025
1978

2153
2182

2415
2414
2431
2433
2433
2433
2432
2471
2432
2414
2415
2436
2436
2436
2436
2436
2548
2607
2607
2607
2607
2607

2607
2596

2669
2663
2711
2663
2570
2601
2633

2633
2704
2663

3 4 5 6 7 8 f

Offspring 3
characters. aolelelelelalelalele S
Rv axeccpiateleceteretete eral AA) ea OLOl) az) eee Ole -| 50
Not-sp....... DL) sd] 4) 6h 10) 8h St... 33
Spite istiedewvs 9) 83) 210} e8iiS|) elle 40
Not-sp....... 7 5) 2) 6] 2) 2)... 23
Sp)s.a:.0 ssstelessre bao is BS Ss Ue ellos 27
Not-sp not-ro “esl. 6}. 5) Wi sie 30
Not-sp ro 6 fie) femme) a Ue | i 13
Sp not-ro..... Bi) Gi) (G2) ie 6: 26
Bp "50 \. Giesis:srs1- AVG 3| 2h ealiy 2. .| 18
sooc he saeodde «| 2) 3] 12] 11) 22) 25) 1 .| 76
INOt=SDi<:c)sislere Pe) i ie) et) yd ayo (as ee 27
Spouses 21) FSO], ya sae alee | 24
Not-spt.....5-|53 4, 4) 6) 8| 6 5) 2)... .|140
SDs crcittersetaleve 2} 4) 4! 3) 6) 10] 4).. 33
Not-8Dis36 2m |ee 4, 12) 3) 2) 7] 14] 5)/.. .| 49
Spee cisrerscretersl| re 1; 10) 8} 3) 4) 2) 1j..}. -|138
Not-sp....... 16} 13} 3] 12) 2] 1)... 47
Spine feicieeeers BSS 5] Ay SS]) Sa ee sliece 31
SFarvcctersceecteral ers 2} 15) 10) 11) 14) 4] 4) 1]. 61
Not-sp......- aye orerei[ ereieil ever} me | MLO) +2 kare 21
Spisferkica. tes Seeltaters | ethee| feverell | RO] leter allen cif coat 8
Not-sp....... eee) 2) Pe SOSGIE airalereyie cl 4
SDisrverctetereretstoxs AN e..|) (Olek) SOlRe Li ios). 17
Not-sp wssres «| 1) 2) 4] -4). 9) 15 Salk-aletel| Oo
Specs -| 3] 4) 2] 1) 13) 14 dalle Bl] xs
Not-sp.....-- 6) Foes WO roc) Ieee) Meee ad O74 me SE Vee 24
SDs ciees S| epee Paeeee 4 ese Vic: | Feet Vd eel ee /asrn) (0 Ot
Not-sp......- | hie Wh 21) Wi DSI ea los 35
iS} Nagao Aoriths Oo Hel) col Lecce Gl) LOW She 28
Josie echo tecestaltes 1}...| 3] 4! 2) 18) 10).. 39
{Not-sp wea ae selleciel| ecieecinolLGl ok 34
Boies ee Aol aif 4) Tol fale eel 28
Not-sp......- tN BR er 13) 17] 1]..|. 32
Spisgeretesterncrets 2} 3) -15] 12). .|. .). 32
Not-sp......- a) Say ae eee 17
SB sieve chetc.eveca soesi| ore Ss] evel evel are eval eral eieyal ovoxe Cer laciloalle 25
IN ehr) Saocekeds|| sl lod) acl sal lets! lo) toa assis 1) 10) 15) 1 27
Speci ciate Dy ieveeille ee 3] 12] 9}.. 25
{Not-sp....... asa ol) S| eae Otis 35
Sp: ped. . tease Ze Sh 32h) Sel) a) zie .| 28
Not-sp not-ro 2) SG)? 6} ALi) 4) 2h eh... 23
Not-sp ro DMG S|) Vee Sl) Wl VZiee 29
Sp not-ro..... rN eae «|| P| in| a 2 em) 19
Spero sere DH Sly Sail), aah 15]! AG aire 32
Sp not-ro..... Os US 1 5 sj i Be ee 21
Sperone prac 8| 5) 5) 11) 14) 6).. 49
Sp not-ro..... 2). 2) iy 4) ee A 13
Spires eiitere RASS Sl A SS Qe 16
SA SE AI HOOO (ool lor Heallecre|| ALI EZ] MS pesls.. 12
Not-sp......- Faces) fa) fall Ota. 17
Specie. ficaers Riel) ee) FAN 16). cilins 13
Not-sp....... Societal SQic4..) eOerSl ci 22
Spdeiancsciaes Palisa fecl salle Heel) TBlieverell) 16]) xelire 13
Not-sp not-ro.|..]..|.. Rellisralisetele col) eu PP) Ga ee 18
No Gp Orso eia|(ore evel eel fore | ese eet] mabe | femme Te mk | foe | Sirdar peed .| 34
Sp’ not-rosceeclerelerol eee eritiecd! tS] ml) 2) 3|) Oley 15
SP! LO siete leretore)| etel| less Pel evaltera loc erect way) aL ||) ceS]| mull eS 23

22789 and 2803 had the same male parent.

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QH Sturtevant, Alfred Henry

Sy Al An analysis of the effects
S88 of selection
BioMed

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