SEX 



99 



original parents were lacticolor female and grossu- 

 lariata male, which on our assumptions must be 

 Ffgg and f/GG respectively in constitution. Since 

 the female is always heterozygous for F, her gametes 

 must be of two kinds, viz. Fg and fg, while those of 

 the pure grossulariata male must be all fG. When 

 an ovum Fg is fertilised by a spermatozoon fG, the 



Ffgg [9] 

 gametes | ^ | 



ffGG[^] 



[fG 

 \fG 



W]ffgg 



/^}— X- 



fs 



FfGg[f] ffGg[^] 



\%)-\-{7.)- 



Ffgg [9] 



Ffgg 

 [9] 



ffGg 



I 1 — — I 1 I 



Ffgg FfGg ffGg ffGG FfGg Ffgg ffGg ffgg 



[9] [f ] W] W] [f] [9] W] [d] 



Fig. i8. 



Scheme of inheritance in the Fi and F2 generations resulting from the cross of 

 lacticolor female with grassulccriata male. The character of each individual is 

 represented by the sex signs in brackets, the black being grossulariata in 

 appearance and the light ones lacticolor, 



resulting zygote, FfGg, is heterozygous for both F 

 and G, and in appearance is a female grossulariata. 

 The zygote resulting from the fertilisation of an 

 ovum ^ by a spermatozoon fG is heterozygous for 

 G, but does not contain F, and therefore is a male 

 grossulariata. Such a male being in constitution 

 ffGg must produce gametes of two kinds,/G and fg, 

 in equal numbers. And since we are assuming 

 repulsion between F and G, the F^ female being in 

 constitution, FfGg must produce equal numbers of 



