The evidence for the gametic interpretations of the self-colored fowl is derived from hybridizations. It will now be presented in detail.
1. SILKIE × MINORCA (OR SPANISH).
(Plates [ 3] to [6].)
By hypothesis this cross is between cJnwx and CJNwx. The first generation should give the zygotic formula CcJ2Nnw2x2, or, more simply, CcJ2Nn. 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) 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 pigmentation 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 (cf. plates [ 1] and [2]).
Since segregation takes place in the gametes of these heterozygotes, 4 kinds of gametes are possible, namely, CJN, CJn, cJN, cJn. On mating heterozygotes together, zygotes of 16 types will be formed, as in table 57.
Table 57.—Zygotes in F2 of Silkie × Minorca hybrids and their corresponding somatic colors.
| C2J2N2 N | C2J2Nn N | CcJ2N2 N | CcJ2Nn N |
| C2J2Nn N | C2J2n2 G | CcJ2Nn N | CcJ2n2 G |
| CcJ2N2 N | CcJ2Nn N | c2J2N2 W | c2J2Nn W |
| CcJ2Nn N | CcJ2n2 G | c2J2Nn W | c2J2n2 W |
Table 58.
| Pen No. | Black. | White. | Game. | |||
| Observed. | Expected. | Observed. | Expected. | Observed. | Expected. | |
| 709 | 119 | 116 | 55 | 51 | 31 | 38 |
| 804 | 91 | 89 | 40 | 39 | 26 | 29 |
| Total. | 210 | 205 | 95 | 90 | 57 | 67 |
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 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 is more striking than to see the hens of this F2 generation with evidences of the female Game pattern ([plate 6]).