PLUMAGE COLOR. 77 



The correspondence is certainly close. The hypothesis of factors thus 

 receives additional support and the variability of the offspring in the second 

 hybrid generation is sufficiently explained. 



4. WHITE LEGHORN X BLACK MINORCA. 



As we have already seen, the gametic formula of the White Leghorn is 

 CJNWx and that of the Minorca is CJNwx, so that the ¥, generation has 

 the zygotic formula C,J,N,Wwx, or, more simply, C,J,N,Ww. These 

 heterozygotes are white because of the graying factor, but, as this factor is 

 diluted, some black shows, particularly in the females. In Fj, on account 

 of there being only 1 heterozygous factor, only 3 kinds of zygotes are formed, 

 C,J,N^W„ CJ,N,Ww, and C,J,N,w„ in the proportions 1:2:1. Since not 

 only offspring homozygous in W, but also all male heterozygotes, are 

 white and many female heterozygotes are late in revealing any pigment, 

 it is necessary to consider together individuals homozygous and heterozy- 

 gous in W. Consequently we may expect 75 per cent of the offspring to 

 show white or white-black-speckled plumage, and 25 per cent black or 

 black and white like the young Minorca. Actually, in 154 offspring (pen 

 633) I obtained 116 white + white-black + blue, and 38 black with more or 

 less white and including 4 barred, of which more later. Expectation is 

 115.5 and 38.5, respectively. 



In another experiment I crossed the Fi hybrids on a pure White Leg- 

 horn and got 41 offspring, all white except 1 that showed some black specks. 

 All results thus accord with h5^o thesis. 



5. WHITE LEGHORN X BUFF COCHIN. 

 (Plate 9.) 



These two races afford the gametic formulae CJNWx and CjnwX, 

 respectively. The Fj hybrids consequently have the zygotic formula 

 C^jNnWwXx. Such hybrids are heterozygous in all factors except C. 

 Such complex heterozygotism, combined with the well-known sex differences 

 in color of heterozygotes, leads to a very great diversity of the offspring. 

 As a matter of fact I found, as Hurst did, that the young were sometimes 

 quite white, sometimes white and buff, and sometimes showed also a Uttle 

 black. Since there are 4 heterozygous characters, there are 256 possible 

 combinations of them, which reduce to 81 different kinds of combinations. 

 Owing to the ambiguous nature of the soma in many of the heterozygotes 

 and to the relatively small number of offspring, it is useless to compare theo- 

 retical and observed distributions of plumage colors in the somas. Suffice 

 it to say that white, buff, black, and Game-colored chicks all appeared in 

 the Fj generation, as well as some with a mixture of colors, as called for 

 by the hypothesis. White, due to the powerful grajdng factor, was the 

 commonest color, buff and black were about equally common, and each 

 about one-third as abundant as white, while Games, due to the hypostatic 

 J factor, were about one-third as common as buff. All this, again, is expli- 

 cable upon our hypothesis and upon none other so far proposed. 



