HEEEDITY AND SEX 



In Drosophila the female is apparently 



homozygous as regards some cell-structure, 



X, which in the male is never represented 



more than once. Accordingly the formula of 



FEMALE MALE 



FIG. 53. Diagram of sex-limited inheritance when the female 

 is a homozygote, as in the red-eyed Drosophila. X, sex- 

 determiner; R, red-eyes. 



the female is in such cases X X ; that of the 

 male, X . Now the sex-limited characters in 

 Drosophila seem to be bound up with the X 

 structure, not repelled by it, as is barring in 

 fowls. Accordingly, a sex-limited character 

 may be represented twice in the female Droso- 

 phila, but only once in the male; or in other 



175 



