io6 



MENDELISM 



the Fi male birds produced by this cross is ffPpIi 

 as before, but the female birds must be all of the 

 constitution FfPpii. The Silky cock transmits the 

 fully pigmented condition to his daughters, because 

 the gametes of the Brown Leghorn hen which con- 

 tain the factor for femaleness do not contain the 

 inhibitory factor owing to the repulsion between 



these factors. The 

 [9]FfppIi ffPPii[^] nature of the regenera- 



tion in each case is 

 in harmony with the 

 above scheme. As, 

 however, it serves to 

 illustrate certain points 

 in connection with in- 

 termediate forms we 

 shall postpone further 



Fig. 23. 



Scheme to illustrate the nature of the Fj , , 



generation from the Brown Leghorn hen consideration of it till 

 and Silky cock (cf. Fig. 22). 



we discuss these 

 matters, and for the present shall limit ourselves to 

 the explanation of the different behaviour of the Fj " 

 males and females when crossed with the Brown 

 Leghorn. And, first, the cross of Brown Leghorn 

 female by Fj male. The Brown Leghorn hen is on 

 our hypothesis FfppIi, and produces gametes Fpi and 

 fpl. The Fj cock is on our hypothesis ffPpIi, and 

 produces in equal numbers the four kinds of gametes 

 fPl, fPi, fpl, fpi. The result of the meeting of 

 these two series of gametes is given in Fig. 24. 

 Of the eight different kinds of zygote formed only 

 one contains P in the absence of /, and this is a 

 female. The result, as we have already seen, is in 

 accordance with the experimental facts. 



