Scheme illustrating the result of crossing a Brown Leghorn hen with a Silky cock (cf. Fig. 19).
When, however, the cross was made the other way, viz. Brown Leghorn hen × Silky cock, the result was different. While the F1 male birds were almost destitute of pigment as in the previous cross, the F1 hens, on the other hand, were nearly as deeply pigmented as the pure Silky
(Pl. V., 2). The male Silky transmitted the pigmentation, but only to his daughters. Such birds bred together gave an F2 generation containing chicks with the full deep pigment, chicks without pigment, and chicks with various grades of pigmentation, all the different kinds in both sexes.
Scheme to illustrate the result of crossing F1 birds (e.g. Brown Leghorn × Silky) with the pure Brown Leghorn.
In analysing this complicated case many other different crosses were made, but for the present it will be sufficient to mention but one of these, viz. that between the F1 birds and the pure Brown Leghorn. The cross between the F1 hen and the Brown Leghorn cock produced only birds with a slight amount of pigment and birds without pigment. And this was true for both the deeply pigmented and the slightly pigmented types of F1 hen. But when the F1 cock was mated to a Brown Leghorn hen, a definite proportion of the chicks, one in eight, was deeply pigmented, and these deeply pigmented birds were always females (cf. Fig. 21). And in this respect all the F1 males behaved alike, whether they were from the Silky hen or from the Silky cock. We have, therefore, the paradox that the F1 hen, though herself deeply pigmented, cannot transmit this condition to any of her offspring when she is mated to the unpigmented Brown Leghorn, but that, when similarly mated, the F1 cock can transmit this pigmented condition to a quarter of his female offspring though he himself is almost devoid of pigment.
1, 2, F1 Cock and Hen, ex Brown Leghorn Hen × Silky Cock; 3, Silky Cock; 4, Hen ex Silky Hen × Brown Leghorn Cock.