THE DETERMINATION OF SEX 279 



during maturation and are then fertilized by a sperm 

 bearing a ^-chromosome, mature into white-eyed off- 

 spring. 



The reciprocal cross of white-eyed females with red- 



Red-eyed Female White-eyed Male 



Gametes 



Tjt "V "V V V "V V V XT 



x"o _^-, _". ** ** **_ -^ -t- .* 



FIG. 85. Criss-cross inheritance. The underscored X means the 

 presence of the genes for red eyes in the sex-chromosome. 

 The male is heterozygous. 



eyed males, gives an entirely different result (Fig. 

 86.) It will be seen that in this case the F t females 

 are red-eyed like their fathers, while the males are 

 white-eyed like their mothers. In the F 2 generation 

 half of the males and half of the females are white- 

 eyed and the others are red-eyed, due to the fact that 

 the male mechanism which has only one ^-chromosome, 



