x SEX 107 



(PL V. , 2) . The male Silky transmitted the pigmentation, 

 but only to his daughters. Such birds bred together 

 gave an F 2 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. 



In analysing this complicated case many other different 

 crosses were made, but for the present it will be sufficient 



(Brown Leghorn) Silky 



9 x 



( Brown Legh.) ^ X ? $ X 9 C Brown Leghorn) 



e? d ? 9 rfe?dd?999 



FIG. 21. 



Scheme to illustrate the result of crossing F t birds (e.g. Brown Leghorn X Silky) with the 

 pure Brown Leghorn. 



to mention but one of these, viz. that between the FI birds 

 and the pure Brown Leghorn. The cross between the FI 

 hen and the Brown Leghorn cock produced only birds 

 with a slight amount of pigment and birds without pig- 

 ment. And this was true for both the deeply pigmented 

 and the slightly pigmented types of FI hen. But when 

 the FI cock was mated to a Brown Leghorn hen, a definite 

 proportion of the chicks, one in eight, was deeply pig- 

 mented, and these deeply pigmented birds were always fe- 

 males (cf. Fig. 21). And in this respect all the FI males 



