HEEEDITY AND SEX 



reduction division. Thus, in the barred Rock, 

 calling barring B, the male of pure race is 

 plainly B B and every sperm is B. But the 

 female clearly contains only one B and can- 



FEMALE 



MALE 



FIG. 52. Diagram of sex-limited inheritance when the female 

 is a heterozygote, as in barred fowls. X, female sex deter- 

 miner; B, barring. 



not be made to contain two. Perhaps a second 

 B is kept out by some structural element, X, 

 the distinctive structural element of the female 

 individual. Then the eggs will be of two 

 sorts: B and X. Since the sperms are all B, 

 the first type of egg when fertilized will con- 

 tain B B, a homozygous barred individual and 



173 



