SEX 



103 



gametes Fpi and fpf, the male birds produced by 

 such a cross should be heterozygous for /, i.e. in 

 constitution ffpplt, while the hen birds, though 

 identical in appearance so far as absence of pig- 

 mentation goes, should not contain this factor but 

 should be constitutionally Ffppii. Crossed with the 

 pure Silky, the F l birds of opposite sexes should 

 give an entirely different result. For while the hens 



C9] Ffppii 



gives 

 gametes 



Fpi \ 



gives 

 gametes 



ffPPii [ 9 ] Ffppii ^/fppli[<5 ] FfPPii [ f ] 



gives 

 gametes 



fPi\ 

 fPi/ 



gives 

 gametes 



f Fpi 

 I fpi 



gives 

 gametes 



gives 

 gametes 



( 



I 



FPi 

 fPp 



FfPpii 



ffPpii FfPpli FfPpii ffPpli ffPpii 



w] m [f] E^] w] 



FIG. 25. 



Scheme to illustrate the heterozygous nature of the pure Brown Leghorn hen. 

 For explanation see text. 



should give only deeply pigmented birds of both 

 sexes, the cocks should give equal numbers of deeply 

 pigmented and slightly pigmented birds (cf. Fig. 

 25). These were the results which the experiment 

 actually gave, thus affording strong confirmation of 

 the view which we have been led to take of the 

 Brown Leghorn hen. Essentially the poultry case 

 is that of the currant moth. It differs in that the 



