drag rien sh oe ite ite 7 seta rater nial ith inte! Se ad 3 oe 1 i ie ie) fet sts Ht nla Bc ae ih oe iH Dat MM Hie eee Ay Oa Wd i) ct Hii i ah Peat ae i caer wt ryt ace ih Pal ne nT eye 1 i h hast i i) ik nay not ia it AM oe nbs if. aa PY Santi “hae ish ie - ere) tan ce ate ae pS Ad ie iti a ¢ rf like a se eins Hite i MEI Th ee Ai aa ei ie - atte Regie yal be HONG POUR pdan pani tg vfs id oti ade isa pen etter it ate sata i . Todi ncen st : siemeh hear oe Perkin sty ey {iter Oa oe ig mca raaare sats MAMMA Spey x rotates : pep eer oath mnbnde/Soiainyerapbrene ye kgcga ine asad teesannrahaelaonsnanseskanrbeorer ssc estes bowimininheie ominiaieraalaate : ‘) Deters pnstowams LoNeiealy Leon r, jinseai tit Aa ate Siac arn hee tate ; , Lr FopanasinanasySiagancgboaenetnegl epetioes ayer asia : sine bebe recep unin onet ee ait a ‘ip rie or espe pings red preaeayyy Pihng-dnparparieere ee rie rebieshaaunpayviniesruieypittrt iene : ei Tnpe ecient s 4 TP perianal, ALBERT R. MANN LIBRARY New York STATE COLLEGES OF AGRICULTURE AND HoME ECONOMICS AT CORNELL UNIVERSITY Date Due ornell University Libra! imo 3 1924 Cornell University The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003067000 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL BY CHARLES B, DAVENPORT WASHINGTON, D. C. PUBLISHED BY THE CARNEGIE InstrTUTION or WasHINGTON 1909 . Cornell University Library OF THE Rew Dork $ Delos College of fgriculture ef See eT ISS ee OTE RTO ws 3514 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. BY CHARLES B. DAVENPORT, Drrecror oF THE STATION FoR EXPERIMENTAL EvoLurIon, Carneain InstTITUTION or WasHINGTON. WASHINGTON, D. C. PuBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON. 1909 5 , A As \ OG " CABNEGIE INSTITUTION OF WASHINGTON PUBLICATION No. 121. PAPERS OF THE STATION FOR EXPERIMENTAL EVOLUTION, No. 14. Gopies of this Book were first issued FEB ¢ 1910 PRESS OF J. B. LIPPINCOTT COMPANY PHILADELPHIA TABLE OF CONTENTS. PAGE INTRODUCTION 1.0.00. 0 ce sees ee eneeeaees Sie SERGE ean ada Gia N enc ad aauemeale RAG AAT MRRCNE ROSE 524 araitro 3 Cuapre1r I. Tam Sprit oR Y COMB 2.1... cece ccc eee eee nner eee nena n eb te tenes 5 A. Interpretation of the Y Comb........ 0. cece cece reece eee ee ene nen e eee een ent n enon tetas 5 B. Variability of the Y Comb and Inheritance of the Variations ........... 6. cece eee ence e eee 12 CHaPren. IT, PoLYDACTYLISM wii ss ce ieee noes cos eae PUR TAN DA ae Re O OEE RS EET O x 17 A. Types:of: Polydactyligm oie ci.cs css axon evs a cusestada seias spake betel ae bioemae ie neneee 17 B. Results of Hybridization........ 0... ccccc cece eee nee een enn n eter ees 18 CHrApren TL SYNDACTYLISN (yi eik pedguss 5 Seoeay Ss geey eye tees Re ee Oey 29 A; Statement: of Problema tsi. ..664.¢-sauauiincw saves ces Jnaieniaminia dn heed Waamuldee’s BE CGE Vieng Maudie ne ge 29 B.- Results of Hybridization «+ + sess ve2s.acas cuemeee 042 4es CHINA eRe ay pe Rhee ee ees reese es 32 CHaprur IV. RUMPLESSNESS: «3 scinciee nceea cee semen eee pe sea SRNR U ENE e aos HOES Cod eae Heme Te Ts 37 CHAPTER. Vz WINGLMSSNEGS 5.55.06 sicisene Sa eas Sues PENS Glace HAN Te mee GRR SHE eo cos Fea vawlee Ree 42 CHaprar VE. BOOTING jis nto sea na fA Sasa BONAR S ORS ease NUR ROE ERAS SS witela Raa OR 43 A. Types’of Booting. « csic cc ceca vadiewsar scaass ainies L204 ss eee we ewes yea cag ks ReOeERaeT EEE 43 B. Normal Variability’ a5. a4 iscapuge nad oad cape ae eng ce aie Pe CAA LO ome t BM ORiemNE ad sas 43 ©, Results of Hybridization ...:..6:2 ccc ice case gneiss secant ns pinwiniee Fo SEE TG TMi EEE Ooo wa baenined os 46 Crapren VII. (NOSTRIRE ORM sisi 5554 drei ene 4 os a a eesancedo nce De wok dep Mal pasion ddis nso aces MyM IS 59 CHapran VIL. CREST o6c5. i catngid uk ued ee eee eee eancsa Gaweed GO st en Rho poSEeR ee oulnes 67 Crapren DX. \COMB-DOP iia eax gs aulteleid- ess yews a agian RU es Medipeway eee Redeeil ets 69 Coarren XX. PromMaGe CovoRins+ s ren ee 8 1; 1 65 |729| 913] F2 6 | 936] Fe 16 5 6 | 16 2 5/.. 3] 11] 11/ 10 66 | 819 57) Fi 4 | 1420] Fe 14 3 2 4 ue 1 3 5] 1 67 |832] 505] Fi 4 /}5119| F3 14 2 2 3 3 2 eee 2 2 2| 4 68 | 729 | 935) Fz 4 | 936| Fe 14 3 5 4 0 3 2 6} 12{ 15] 3 69 | 756 | 2011| Fo 4 | 444) Fe 14 rae gee Ls Sege Ll ee 1 1 4/ 3 70 |807| 185) Fi 4 | 3894) Fs 13 4 BN cece ee 2 1 1 2; 1 71 +|756 | 1048} Fa 3 | 1390 | Fe 13 wa | $4 3 Pea eal eee ae ere 2 |) 33 72 |762| 505 3 | 444] Fe 13 1 1 3 1 1 2 2 2 3) 4 73 | 762 | 2011) Fs 4 | 2621) Fz 9/ 13 Ml ase olla sas all deat tem L 1 3) 1 74 | 813 | 2271) Fe 5 | 3904] Fs 7 | 12 1 5 5 2 2 1 3 2 4; 9 75 |820) 984] Fe ...| 8 14731] Fs 9} 12 iyi 5 4 2 5 Te a's 5 5| 4 76 | 728 |2272}| Fe |..Do......... 10 | 258] Fi 2] 12 2 7 9 4 4 3 2 7 7| 9 77 =+| 766 | 1043] Fz 2 |1390| Fo | PXM 10 | 12 5 5 3 2 eee | ay} we 3 2| 2 78 |762) 505 3 9 a St emer Geren (eee am ae Pe as | ee sail 33 79 | 803 | 2250| Fe 3 9 ar 5 2 2 BEN atee sf avs 4 9| 6 80 | 803 | 2254] Fe 3 9 6; 4/ 1] 2] 1 1; 3 6| 3 81 | 769 | 492] Fi 2 9 | 6 1 be eee Dl) ee alin ah eer 82 | 807 | 1043) Fa 2 9 4 2.| as 3 3 | x2 6 6|.. 83 | 769 | 2254! Fe 1 9 7 2 Delt. eee 1 2 4; 1 84 |813|] 935| Fa 3 7 2 ee 4 4 meee 7 8; 1 85 {813 |5113] Fs 3 a 5 Bit aa 1 1 1 6 8] 5 86 | 813 | 5142| Fs 3 7 7a fae eres a al | (ee 1 1| 3 87 | 813 | 5122) Fs 2 7 1 2) as 1 2 2! 3 88 | 813 | 7320| Fs |.. 2 7 6 bie neers 1 2 5| 2 89 |813 | 377) Fi |.. 1 7 ne 6 p Coa eres 1 4 3]... Totals (641) 86 | 80 | 29 | 38 | 24 | 23 | 95 | 119} 79 POLOPMA ROR atv o vunin as tem eaay pees eH aig ig a -6]13.4/12.5/ 4.5 | 5.9 | 3.7 | 3.6 |14.8/18.6|12.3 41.0 59.0 NOSTRIL-FORM. 63 TaBLE 52.—Distribution of frequency of grades of “openness” in offspring when both parents are extracted dominants (extracted DDX DD). [ABBREVIATIONS: H=Houdan; L=Leghorn; M=Minorea; P = Polish; WL= White Leghorn.] Mother. Father. Total Grade of openness in offspring. Races. Races. gr. Totals (472) Percentages, > oe ee ees ‘1 1 9 1.9 > woe: Per. soe 8 1.7 Ce CnC re a Cr Poo de cots gh WS | ww wit o | | ae NNPNE RR OOO OPWOPRN TARO EEK OR RARDWHAOHKA mons oh: me ONE RNNH OHH: Dawa: eee » Or NN 5| 7 10 5 93 19.8 aH ew: wma: wo: _ 7 Is 169 36.0 - So nN No wt TaBLE 53.—Distribution of frequency of grades of “openness”’ in offspring when both parents are heterozygous (RRXDR). Mother Father. Grade of openness in offspring. No. Races. Grade, Races. Grade, to 174 912 3799 509 3846 5025 5087 Houd. X Legh. soda I Ov siioias 9:8 Min. X Houd,. Polish X Min. . Totals (217) Percentages NNNRKONH Brah. X Tosa.. Houd. X Legh, | e OCOaeanwr 1 2 1.6 2 1.6 oo an Tas iE extracted recessives (extracted RRXRR). 54.—Distribution of frequency of grades of “openness” in offspring when both parents are Serial No, Pen Mother. Father. No. No. Gen. Races. Grade. Gen. Races. Grade. Offspring. Grade 1 Grade 2 128 129 728 827 #912 298 F2 F2 Houd. X Legh. Pol. XMin.... F2 2 F; Houd. X Legh. * Cf. Serial No. 12a, 64 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. even show the typical narrow nostril (fig. B, a). On the other hand, in the narrow-nostriled races I have never obtained any such variation. The most deviation that I have seen from grade 1 is found in my strain of Dark 12345678910 12345678910 40 Ny 30 ae e a 20 20 10 10 KRW ae _ RSE o SQLs 160 : 150 / 140 30 : 130 20 120 10 Nag ORR 110 Ni (0) INE ——— 100 b 90 ExtrDDxDD J g 80 40 70 30 WSS 60 20 Sy DRXRR (extr) 50 10 40 \ (0) 30 : : 20 RR a IN 10 0 NN 9 KN RR*RR | 10 100 v 90} KY PR*DD RS 20 80 10 KER DRxD _ ¢ 70 ~ 0 USE 60 SS 50 k 40 180 BINNS 20 S 160 10 150 0 140 130 130 120 120 110 ETRrae Ho SS 100 1 DR 100 F2 (DRX DR) 90 90 80 SSQy 80 dz S 70 60 60 = 50 50 SS 40 40 N Ne 30 30 N 20 aR 20 Oo SX IS \S 0 . (2345678910 '2345678910 Fie. B.—Polygons of frequency of grades of ‘‘openness” of nostril in offspring of various parents. a, Both parents pure bred dominants; b, both parents extracted dominants; ¢, one parent heterozygous, the other a domi- nant; d, both parents heterozygous; e, dominant by recessive; f, heterozy- gous by recessive; g, heterozygous by extracted recessive; h, extracted shart eg: i, heterozygous by dominant; k, both parents second generation ybrids, Brahma bantams that fre- quently give grade 2. The variability of the high nos- tril, the stability of the low nostril, is prima facie evi- dence that the former is due to the presence of a particu- lar factor and the latter to its absence. Next, the heterozygotes of F, (table 46), may be ap- pealed to; but they will give no critical answer. For ex- pectation, dominance being imperfect, is that the hybrids will be intermediate, and the result will be the same which- ever extreme grade is taken as dominant. The empirical mode in the distribution of the offspring is at grade 2. This implies much greater imperfection of dominance on the hypothesis that grade 10 is dominant than on the hypothesis that grade 1 is dominant; but this very fact ‘supports the former hypoth- esis, since imperfection of dominance is obviously a feature of the character with which we are dealing. The critical test is af- forded by the F, generation (tables 48 and 49). By hy- pothesis, 25 per cent of the offspring are expected to be pure (“‘extracted’’) recessives, and the same number pure dominants; and also, by hypothesis, the recessives are massed at or near one grade while the domi- . nants are variable. Now, as a matter of fact, the upper 25 per cent range over 5 to 7 grades, while the lower 25 per cent are nearly massed in grade 1 NOSTRIL-FORM. 65 (21 per cent are so massed in one table, 17 per cent in the other). Therefore, in accordance with hypothesis we must regard the lower grade—narrow slit—as recessive. Similarly, heterozygous X low nostril (table 47) should give, on our hypothesis, 50 per cent low nostril. If that is recessive we should expect a massing of this 50 in the first two grades; if dominant a greater scattering. The former alternative is realized. Again, in the heterozygous x high nostril hybrid (table 50) the upper 50 per cent will be massed or scattered according as high nostril is recessive or dominant. Allowing for the 50 per cent heterozygotes in the progeny, the 50 per cent of high nostrils are scattered through at least 8 grades of the possible 10. High nostril is dominant. Finally, extracted high nostrils bred together produce off- spring (table 52) with a great range of variability (through all grades), while extracted low nostrils (unfortunately all too few) give progeny with grades 1 and 2 (table 53; fig. B, h). Accepting, then, the general prin- ciple of the greater variability of the dominant character, we have demon- strated conclusively that high nostril, or rather the factor that determines high nostril, is dominant. Comparing tables 45 to 54, we see that recessive parents are character- ized by a low grade of nostril and they, of course, tend to produce offspring with a low grade. Similarly, dominants have a high grade and tend to produce offspring of the same sori, while heterozygous parents are of inter- mediate grade and their children have nostril grades that are, on the aver- age, intermediate. Without regarding the gametic constitution, we might conclude, with Castle, that offspring inherit the grade of their parents, and consequently it would be possible to increase the grade, perhaps indefi- nitely, by breeding from parents with the highest grade. Considering the gametic constitution of the parents, it is obvious that such a conclusion is premature. To get an answer to the question it is necessary to find if there is, inside of any one table, among parents of the same gametic consti- tution, any such relation between parental and filial grades. This can be determined by calculating the correlation between the grades of parents and progeny. Such calculation I have made for table 48 with the result: index of correlation, r=0.018 + 0.032, which is to be interpreted as indicat- ing that no correlation exists; and in so far the hypothesis of Castle proves not to apply in the cases of booting and doubt is thrown on the significance of his conclusion. Finally, if we throw together the frequency distributions of all tables into one table (table 55; compare fig. B) we shall find the totals instruc- tive. Table 55 shows that, when all results are thrown together, including hybrids of all sorts, grade 2 and grade 9 are the most frequent and grade 6 is the least frequent, the frequency gradually rising towards the extremes of the series. The same result appears in the individual series that range from grade 1 to grade 10. What is the meaning of this result? It seems to.me to bear but one interpretation, namely, that there are only two centers 5 66 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. of stability—about grades 1 and 9—and true blending of these grades, giving an intermediate condition, does not occur. Otherwise, in conse- quence of the repeated hybridization, the intermediate grades must be the commonest instead of the rarest. There is alternative inheritance of the nostril height. TasBie 55.—Summary of tables 45 to 54. ABSOLUTE FREQUENCIES. Grade of openness in offspring. Table} Nature of mating (parental Nature of No. nostril). muting. 1 2 3 4 5 6 7 8 9 10 |Total 45 | Mich Xhithisacciasvawwwns oa DR Dies viaxee 2 2 1 1 6 5 8} 28 | 39 | 27] 119 AG | TUS HlOW naam ase hda ery 6 DR Rie xpac aes 13 19 9 7 2 4 1 1 arate 56 47 23 | 14 9 2 4 bts oo 53 48 90 | 140 | 86; 20] 21 18 9 13 17 6 | 420 49 117 | 171 | 129 | 54] 40 11 19 | 39] 57 | 41 | 678 50 10 13 10 5 4 1 8 6 2 61 51 71 96 73 30 39 24 23 95 | 119 68 | 638 52 ere en aed 9; 19} 18] 15 14 8 | 22] 93 | 169 | 105 | 472 53 | Heterozygous X extracted low.| DR XRR. .. 40 35 26 7 3 1 es é 112 54 | Extra low Xlow,............-. RRXRR.,.... 8 Be il) Mice aves a iain vase ; 16 TAGS easeus se eenece as uae eekeea's waa 378 | 512 | 361 | 141 | 133 72 85 | 277 | 407 | 249 PERCENTAGES. Grade of openness in offspring. Nature of mating (parental Nature of Table nostril). mating. No. 1 2 3 4 5 6 7 8 9 10 45 | High highwssevss se vesenr aes De Das ve xens 1.7] 1.7] 0.8) 0.8} 5.0) 4.2] 6.7) 23.5 /32.8/22.7]... AG | High Xlow. nese cnviacasisnns DR Rye ax aes 23.2 /34.0/16.1/12.5| 3.6] 7.1] 1.8] 1.8)....].... " 47 | Heterozygous Xlow........... DRXR...... 43.4|26.4/35.9| 3.8] 7.6]....] 1.9]....]....] ease] eee 48 | Heterozygous X heterozygous...}; DR XDR.....| 21.5 | 33.3 | 20.5; 4.8} 5.0) 4.3] 2.1] 3.1) 4.1] 1.2]. 49 17.3/25.2/19.0] 8.0] 5.9] 1.6/ 2.8] 5.8] 8.4) 6.1]. 50 16.4] 21.3/16.4] 8.2] 6.6| 1.6] 3.3/13.1] 9.8] 3.3]. 51 «{11.1]15.1]11.4] 4.7] 6.1] 3.8] 3.6)14.9/18.7]10.7]. 52 wees} 1.9] 4.0] 3.8] 3.2] 3.0] 1.7] 4.7/19.7| 35.8 | 22.2]. 53 | Heterozygous X extracted low.| DR XRR.....| 35.8 | 31.3 | 23.2] 6.3] 2.7) 0.9]....}....]....]...0]- 54 | Extracted low Xlow.......... RRXRR,,«::. (50.0: | 50.0 | occ | sess [eww [cons CHAPTER VIII. CREST. In my report of 1906 I called attention to the nature of inheritance of the crest in the first and second generations. The result seemed simple enough on the assumption of imperfect dominance. However, in later generations difficulties appeared, one of which was referred to in a lecture given before the Washington Academy of Sciences in 1907. I stated (1907, p. 182), that ‘when a crested bird is crossed with a plain-headed one, and the crested hybrids are then crossed inter se, the extracted recessives of the second hybrid generation are plain-headed, to be sure, but they show a disturbance of certain feathers.”” This was an illustration of the statement that recessives which are supposed to come from two pure recessive gametes show in their soma traces of the dominant type. Dr. W. J. Spillman, who was present, made the suggestion that the crest is composed of two char- acters, T and t, instead of a simple element, and that when ¢ alone is present the result will be the roughened short feathers on top of the head. Further studies demonstrate the validity of this suggestion. There are in the crest two and probably three or more factors. There is a factor that deter- mines length of the feathers and a factor that determines their erectness. There is probably also an extension factor that controls the area that the crest occupies on the head. Thus flatness of position dominates over its absence (or erectness). This is seen even in the first generation. Figs. 5, 6, 8, and 17 of my report of 1906 show this very plainly. They also show that continued growth of feather is dominant over interrupted growth. Thus in the second hybrid generation I got birds with short and erect feathers and one of these is shown in fig. 11 of the 1906 report. That shortness is recessive is proved by various matings of extracted short x short crest. Of 29 offspring none have a higher grade than 1, grade 10 being of full length. On the other hand, two parents with long feathers in the crest (grades 6 to 8) give 5 offspring of grade 1, 12 of grades 5 to 10, thus approach- ing the 1 : 3 ratio expected from two DR parents. That erectness is reces- sive is proved by various matings of extracted erect x erect crest. Of 25 offspring none has a lower grade than 4 (1 case) or 5 (1 case). On the other hand, two parents with extracted non-erect feathers give in 46 offspring 13 with feathers whose grade of erectness is 6 or higher and 33 with a grade of 5 or below—of these half of grade 0—close to the expected 1:3. The evidence is conclusive that there are two factors in crest that behave in Men- delian fashion—a factor determining the prolonged growth of the feather and a factor causing the feathers to lie repent. 67 68 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. The area of the head occupied by the crest is also variable. This was estimated in tenths for each of the parents and offspring. Two principal centers of variation appeared, at 3 and at 8, or roughly one-third and two- thirds the full area. The results, being based on estimates, are not wholly satisfactory, but so far as they go they indicate that when both parents have a crest that belongs to the lower center of variation their offspring belong chiefly if not exclusively to that center; but when they both belong to the upper center of variation a minority of the offspring belong to the lower center. Provisionally it may be concluded that extensive crest is dominant over the restricted crest or that there is an ‘extension factor.” CHAPTER IX. COMB-LOP. In races having a large single comb this is usually erect in the male, but in the female lops over to the right or left side of the head. This lop is determined before hatching; indeed, in the male it may be ascertainable only in the embryo or in the recently hatched chick. The position of the comb is permanent throughout the life of the pullet and hen and, if pressed to the opposite side, it quickly returns to its original position. At one time I entertained the hypothesis that its position was determined by the pres- sure of the foot against the head while the chick was still within the shell; but after finding the comb lying both to the right and to the left when in contact with the foot I abandoned this hypothesis as untenable. It seemed possible that this position is hereditary, and so data were collected to test this hypothesis. It is not always easy to decide definitely, even for the female, as to the direction of the lop; for the anterior part of the comb may lop to the right, the posterior part to the left, or vice versa. In that case one selects the larger or better defined lopping portion to designate as the lop. This is usually the posterior portion of the comb. However, such doubtful cases may be omitted from consideration here, as there are plenty of examples of well-defined lop on both sides of the head. TaBLE 56. Both parents with right lop. Mother left lop, father right. Offspring. Offspring. No. of | No. of No. of | No. of Pen No. | mother. | father. Pen No. | mother. | father. Right. Left. Right. Left. 817 6188 3900 7 8 831 1980 4213 9 17 817 6406 3900 12 17 904 3901 7840 4 3 831 1011 4213 7 16 904 7645 7840 6 3 831 3040 4213 13 10 19 23 831 4219 4213 4 21 4213 6 15 ; a sed 4222 4 7 Mother right lop, father left. 833 | 4361 | 4222 s by 903 | 3946 | 8463 2 0 833 | 7519 | 4222 Fi - 903 | 4079 | 8463 7 2 904 | 4714 | 7870 S é 903 | 4082 | 8463 UW 6 67 109 20 8 Summary. Both parents with left lop. Offspring. Parents. Total. | Right} Left. 841 3867 3890 3 9 P.ct.| P. ct 841 4663 3890 9 7 Both with right lop....,-- 176 38 62 903 9824 8463 6 5 Both with left lop......... 39 46 54 Mother left lop, father right| 42 45 55 18 21 Mother right lop, father left 28 71 29 69 70 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. From table 56 it appears, summing all cases, that there are more left- lopping offspring than right-lopping as 161 to 124 or as 56.5 per cent to 43.5 per cent and that this excess holds whether both parents are right- lopping, or both left-lopping, or the mother left and the father right. Only in the case when the mother is right-lopping is there a majority of offspring of the same sort, but here the numbers are too inconsiderable to carry much weight. Although there is not clear evidence of any sort of inherit- ance, it is probable that the position of the lop is not determined by a single factor, but by a complex of factors. The conclusion that right and left conditions are not simple, alter- native qualities accords with the results obtained by others. Thus Larrabee (1906) finds that the dimorphism of the optic chiasma of fishes (in some cases the right optic nerve being dorsal and in others the left) is not at all inherited, but in each generation the result is strictly due to chance. This is, perhaps, the same as my conclusion that the hereditary factors are complex. Lutz (1908) finds that in the mode of clasping the hands inter- digitally the right thumb is uppermost in 73 per cent of the offspring when both parents clasp with right thumb uppermost, but in only 42 per cent of the offspring when both parents clasp with left thumb uppermost. The mode of clasping is inherited, but not in simple Mendelian fashion. CHAPTER X. PLUMAGE COLOR. A. THE GAMETIC COMPOSITION OF THE VARIOUS RACES. Plumage color, like hair color, varies greatly among domesticated animals. This diversity is, no doubt, in part due to the striking nature of color variations, but chiefly to the fact that the requisite variations are afforded in abundance. The principal color varieties, in poultry as in other domesticated animals, are melanism, xanthism, and albinism. In addition, poultry show the dominant white, or “gray” white, first recognized in poultry by Bateson and Saunders (1902), which is also found in many mammals, as, for instance, in goats, sheep, and cattle. Besides these uniform colors, we find numerous special feather-patterns, such as lacing (or edging of the feather), barring, penciling, and spangling. Also, there are special patterns in the plumage as a whole, such as wing-bar, hackle, saddle, breast, and top of head (crest). Now, all of these color characters are inherited each in its own definite fashion. In studying the color varieties of poultry we must first of all, as in flower color (Correns, 1902), mice (Cuénot, 1903), guinea-pigs and rabbits (Castle), various plants and animals (Bateson and his pupils), recognize the existence of certain “factors.”’ In poultry the factors that I have determined are as follows: C, the color factor, absence of which results in albinism. J, the Jungle-fowl pattern and coloration. N (nigrum), the supermelanic factor. X, the superxanthic or “ buff ” factor. W, the graying (white) factor. We have now to consider how these factors are combined in birds of the different races. 1, WHITE. Albinos.—These seem to be of two different origins:* White Cochins and white Silkies. The white Silkies that I have studied have the gametic formula cJ nwa; 1. e., they have the Jungle-fowl marking, but lack the “color enzyme,” supermelanic coat, the graying factor, and the xanthic factor. “Grays.”—White Leghorns and their derivatives belong to this class. Its gametic formula is: CJNWz. This indicates that the race contains the * Bateson and Punnett (1908, p. 28) recognize three “kinds ’’ of recessive whites—that of the Silkie, that of the Rose-comb bantams, and that of “white birds that have arisen in the course of our experiments.’’ White Cochins have perhaps been one of the ancestors of Rose-comb bantams; Bateson’s new white lay recessive in the White Dorking and when mated to the White Silkie throws Game-colored offspring. 71 72 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. color enzyme, as well as the Jungle pattern and the supermelanic coat. But all of these are rendered invisible by the graying factor W. The super- xanthic factor is missing. 2, BLACK. The uniform black birds that I have studied are of several sorts. The Black Minorca and White-faced Black Spanish have the gametic formula CJNwz. Owing to the absence of the graying factor and the presence of the color factor these appear as pigmented birds, but the supermelanic coat, N, obscures the Jungle coloration, so that the bird appears entirely black. Nevertheless the black is not of uniform quality, but just those parts of the feathers of the wing, back, hackle, saddle, and breast that are red in the Jungle fowl are of an iridescent black, while the portion that is not red in the Jungle is of a dead black. The Black Cochin has the gametic formula CINwz. This differs from the formula of the Minorca only in this respect: the Jungle pattern is present, but not the pigmentation that is usually associated with it. The Black Game (“Black Devil’’) that I used in a few experiments seemed to have the same gametic formula as the Minorca, only the super- melanic coat was less dense. 3. BUFF. For this color I used Buff Cochins, the original buff race. The gametic formula of this race proves to be CjnwX—the Jungle-fowl pattern being absent. B, EVIDENCE. The evidence for the gametic interpretations of the self-colored fowl is derived from hybridizations. It will now be presented in detail. 1. SILKIE X MINORCA (OR SPANISH). (Plates 3 to 6.) By hypothesis this cross is between cJnwx and CJNwz. The first generation should give the zygotic formula CcJ,Nnw,z,, or, more simply, CeJ,Nn. This formula resembles closely that for the Minorca; but it differs in this important respect, that the coloring factor and the supermelanic factor are both heterozygous, and hence diluted. Actually I found, as Darwin (1876) did, that the chicks of this first hybrid generation were all wholly black. In this respect they differed markedly from the chicks of the Silkie, which are pure white, and also from the chicks of the Minorca, which are prevailingly black, but have white belly and outer primaries. The white in the young chicks of Minorcas is extremely variable in amount, but never wholly absent; in time, as the bird grows older, it is replaced by black, so that the adult male and female Minorcas have a wholly black plumage. The reason for the precocious development of black pigment over the belly and primaries of the hybrid chicks is probably the presence of an extension factor (cf. Castle, 1909) PLUMAGE COLOR. 73 derived from the Silkie. Certain it is that the ordinary Jungle pattern develops pigment on the belly and on the wings, as well as on other parts of the plumage. The hybrid chicks may be said to have the extended pig- mentation dominant over interrupted pigmentation. In the adult hybrids a difference appears between the coloration of the male and female, even as Darwin pointed out. For the latter retains its uniform blackness, while the former gains red on the wing-bar, and saddle and hackle lacing (plate 4). Now, since all the factors present in the Minorca, and none others, are present in the hybrids, why should the male hybrids show red, and why should the males show red and not the females? The answer to the first question is, I think, clear. While the Jungle pattern of black and red is completely obscured by the undiluted N factor of the Minorca, it is only incompletely covered by the diluted, heterozygous N factor of the hybrid. Hence the red appears in greatly reduced amount, as compared with the Jungle-fowl. In the female Jungle-fowl there is little red and consequently none shows in the female hybrid. Thus the difference in the sexes of the hybrids corresponds to the sexual dimorphism of the Jungle- fowl; but the hybrids are, as indicated, very unlike the Jungle-fowl in coloration (cj. plates 1 and 2). Since segregation takes place in the gametes of these heterozygotes, 4 kinds of gametes are possible, namely, C/N, CJn, cJN, cJn. On mating heterozygotes together, zygotes of 16 types will be formed, as in table 57. TaBLE 57.—Zygotes in F, of Silkie X Minorca hybrids and their corresponding somatic colors. | CoJ2Ne2 N C2J2Nn N CeJ2N2 N CeJ2No N ) C2J2Nn N C2Jonz G CeJ2Nn N CeJonz G | CeJ2Ne N CeJ2Nn N c2J2N2 WwW e2J2Nn Ww | CeJ2Nn =N CeJzn2 G e2J2Nn Ww cadens Ww In the foregoing table there is given after each combination a letter: N standing for black, the appearance of the soma; G standing for Game- colored, and W standing for white. No distinction is made between pure blacks and those that, while black as chicks, subsequently show some red in the male. Such a distinction was impracticable because most of the color Tas ie 58. Black. White. Game. Pen No. Observed. | Expected. | Observed. | Expected. | Observed. | Expected. cit 119 116 55 51 81 38 Sera 91 89 40 39 26 29 Total.... 210 205 95 90 57 67 determinations are made on the young chicks. It appears that in 16 progeny expectation is 9 black, 4 white, and 3 Game-colored. Actually 362 offspring were obtained, with the results shown in table 58. Nothing 74 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL, is more striking than to see the hens of this F, generation with evidences of the female Game pattern (plate 6). Comparing observed results in the distribution of colors in the F, generation with expectation, it is seen that the proportions are close, and this closeness of observation with expectation is evidence for the correct- ness of the hypothesis. The hypothesis may be further tested in later generations by breeding together the different sorts of individuals obtained in F,. In pursuance of such a test I mated various pure black hens with pure black cocks and those of F,, and, as was to have been expected, obtained families of different sorts, simply because even pure blacks have differing gametic constitutions. Thus in pen 824 I mated an extracted black cock with 3 black hens. All were apparently of the zygotic constitution C,J,Nn, forming gametes CJN and CJn. Mated together these should give the three black combinations C,J,N,, C,J,Nn, C,J,nN, to one Game, C,J,n,. Actually there were obtained 64 black and 23 Game, 66 to 22 being expec- tation. In another pen (pen 804) an F, cock was mated to various black F, hens. The families fall into 2 classes. The cock, of course, produced gametes CJN, CJn, cJN, cJn. With four females like him (Nos. 3902, 3908, 5431, 6043) I got: black 40, white 18, Game 14; expected, black 38, white 17, Game 13. Three females (Nos. 4715, 4716, 5099) evidently pro- duced gametes CJN, CJn. Expectation is that blacks and Games shall be produced in the proportions of 3 to 1. Actually 30 : 14 were obtained where 33:11 was expected. All of these results accord closely with the hypothesis. The whites obtained in F, are of 3 types, but in all alike the color factor ig missing. Hence it can not reappear in the offspring, and, consequently, no colored offspring are to be expected. But, first, it must be stated that the extracted whites of the F, generation are not always of a pure white. Indeed, the parent Silkies are in some cases not perfectly white, but show traces of “smoke.”’ There are different degrees of albinism; the coloring enzyme may be absent to small traces. This variability in degree of albinism is familiar to all students of albinism in man. My breeding of extracted whites was done in pen 817 and consisted of a pure white cock (No. 3900) and 2 hens. Of these 1 (No. 6046) was pure white and produced in a total of 15 only white offspring, but among those that were described as unhatched I have recorded traces of pigment in 24 per cent of the cases. The second hen (No. 3899) had black flecks in the white plumage. She had 20 offspring, of which 2 (unhatched) are recorded as having N down, 2 as “blue,” and 3 others show traces of black pigment. Thus, 7 birds in 20, or 35 per cent of all, show more or less black, even as the albinic mother does. On the whole, however, omitting from present consideration the phenomenon of incomplete albinism, we may say that 2 pure albino parents produce only albinic offspring, while imperfectly albinic parents produce some imperfectly albinic offspring. PLUMAGE COLOR. 75 2, SILKIE X WHITE LEGHORN. By hypothesis this cross is between cJnwxz and CJNWz. The first generation should give the zygotic formula CcJ VnWw2z,, or, more simply, CeJ,NnWw. This formula resembles closely that of the White Leghorn, except that the coloring and graying factors and that for supermelanism are all heterozygous and hence diluted; only the J ungle coloration remains unchanged. Actually, the first generation yielded a lot of white birds like the Leghorn, but with this difference, that, as the males became mature, they gained red on the wing-bar and to a slight extent on the lacing of the saddle. The females gained a faint blush of red on the breast. Thus red appeared, in small amount, in just those places in the respective sexes which are red in the Jungle-fowl. The explanation of its appearance that I have to suggest is that, both on account of the diluting of the super- melanic coat and of the graying factor, the red of the undiluted underlying Jungle coloration is revealed. Since the hybrids are heterozygous in respect to 3 pairs of characters, when segregation occurs each parent produces 8 kinds of gametes, as fol- lows: CJUNW, CJNw, CJnW, CJnw, cJNW, cJNw, cJnW, cJnw. When both parents produce these 8 kinds of gametes we may expect, in 64 offspring, the proportions of the several types shown in table 59. Tasie 59.—Probable frequency in 64 progeny. Zygotic formula.| White.| Ye |Game. | Black. |) zygotic formuta,| White.| Vite | Game, | Black. CoJ2N2We.,.... 1 a ah “a CeJ2N:Ww..... 4 er ‘3 s04 CoJ2N2Ww..... 2 ee =e ie CeJ2Now2...... ae pis asta 2 CoJoNeows2....022) 0 +: aA ai 1 CeJoNnW2..... 4 oe ay Be CoJ2Nn We. 2 ns fe ike CeJ2NnWw.... o 8 C2J2Nn Ww. 4 os CeJoNnw2...... 4 C2JoNnw2...... ate 2 CeJon2W2...... 2 CzJon2W2...... 1 a ace ay CeJon2Ww..... ae 4 - CoJon2Ww....--| ++ 2 ha es CeJanaw2....---| ++ mG 2 CoJon2w2....0.. oe ‘est 1 eae C2oJ2—. 0-6-0 6e 16 ns a CeJ2N2W2 2 ot < Total (64)..} 34 18 9 3 While, if the progeny were all to survive to maturity, we might expect to get the proportions of white and of white-and-red progeny called for, yet, since the red color appears in most cases at an age ajter the chicks are described, it will be necessary in comparing experience with calculation to combine the first two classes as whites. We then find the proportions given in table 60. TaBie 60. In the actual 85 In 64 individuals. Color. calculated. Calculated. | Observed. WHI 6s fesecstiscsions 52 69 68 Game............. 9 12 16 Blacks. «scene's «cine 3 4 1 76 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. The proportion of whites agrees closely with expectation. If this is not the case with the other two classes, the discrepancy must be attributed in part to insufficient observations and in part to the difficulties of precise classification in the early stages. The result is so close, however, as to lend strong support to our hypothesis as to the gametic constitution of the parents. Nothing is more striking, and to the unprejudiced mind more convincing, than the appearance of typically Game-colored birds in the grandchildren of wholly white parents. 3. SILKIE