SEX 



103 



£.1; 



ffGg must produce gametes of two kinds, fG and fg, in 

 equal numbers. And since we are assuming repulsion 

 between F and G, the Fi female being in constitution 

 FfGg, must produce equal numbers of gametes Fg and 

 JG. For on our assumption F and G cannot enter into 

 the same gamete. The series of gametes produced by 

 the Fi moths, therefore, a.re fG,fg by the male and Fg,fG 

 by the female. The resulting F2 generation consequently 

 consists of the four classes of zygotes Ffgg, FfGg, ffGg, and 

 ffGG in equal numbers. In other words, the sexes are 

 produced in equal numbers, the proportion of normal 

 grossulariata to lacticolor is 3 : i, and all of the lacticolor 

 are females ; that is to say, the results worked out on our 

 assumptions accord with those actually produced by ex- 

 periment. We may now turn to the results which should 

 be obtained by crossing the Fi moths with the lacticolor 

 variety. And first we wiU take the cross lacticolor female 

 X Fi male. The gametes produced by the lacticolor 

 female we have already seen to be Fg and/g, while those 

 produced by the Fi male are fG and fg. The bringing 

 together of these two series of gametes must result in 

 equal numbers of the four kinds of zygotes FfGg, Ffgg, 

 ffGg, an'd ffgg, i.e. of female grossulariata and lacticolor, 

 and of male grossulariata and lacticolor in equal numbers. 

 Here, again, the calculated results accord with those of 

 experiment. Lastly, we may examine what should hap- 

 pen when the Fi female is crossed with the lacticolor 



