64 



HEREDITY AND SEX 



With these white-eyed females it is possible to make 

 the reciprocal cross (Fig. 36). A white-eyed female 

 was mated to a red-eyed male. All of the daughters 

 had red eyes and all the sons had white eyes. These 

 were then inbred and gave red-eyed males and females, 



XX 



X 



XX XXX 



Fig. 35. — Sex-linked inheritance of white and red eyes in Drosophila. 

 Parents, white-eyed $ and red-eyed 9 ; -^i. red-eyed $ and 9 ; F2 red- 

 eyed 9 , red-eyed $ and white-eyed $ . To right of flies the history of the 

 sex chromosomes XX is shown. The black X carries the factor for red 

 eyes, the open X the factor for white eyes ; the circle stands for no X. 



and white-eyed males and females in equal numbers 

 (Fig. 36). 



The heredity of this eye color takes place with the 

 utmost regularity, and the results show that in some 

 way the mechanism that is involved is closely bound 

 up with the mechanism that produces sex. 



