250 



BREEDING 



was first suggested by Professor Castle.* According 

 to Professor Castle, sex was represented by a factor in 

 the germ-cells exactly as a Mendelian character is. 

 (The factor for maleness will be written (J, and that for 

 femaleness $.) He supposed that both male and female 

 were heterozygous for sex, i.e. both were of the zygotic 

 formula ^ ?. He accounted for the equality in the num- 

 bers of the sexes by supposing that, in about half the 

 zygotes, maleness was dominant, and in the other half 

 femaleness was dominant. He also supposed that, 

 when these heterozygotes mated, the unions between 

 like gametes were infertile, because it was his theory 

 that each sex had the formula <? ?? and it was there- 

 fore necessary to explain the non-existence of the 

 zygotes c?(? and ?$ which, according to the ordinary 

 Mendelian scheme, would result from the union of 



<J? and (J?, thus : — 



Gametes of male 



3 ? 



a3 



a 



4^ 



a> 



a 



eg 



It will be seen that this theory involves two serious 

 assumptions ; first, the altemativeness of dominance 



* Castle, W. E. "The Heredity of Sex." Bull. Mus. Comp. Zod. 

 Harvard, 903. Vol. xl., No. 4. 



