THE DETERMINATION OF SEX 281 



known example of a sex-linked character, behaving in 

 its inheritance exactly as that of red-eye in Drosophila. 

 That color-blind females are so rare is due to the fact 

 that it requires a duplex, or homozygous, dose of the 

 determiner for color-blindness to produce a color-blind 

 female, while only a simplex, or heterozygous, dose is 



Gametes 



Gametes 



FIG. 87. General diagram for sex-linked inheritance. The under- 

 scored symbol (X) represents a sex determiner with some 

 other character (as color-blindness) linked with it. 



needed to produce a color-blind male. These facts 

 agree perfectly with the idea that the female is homo- 

 zygous and the male heterozygous with respect to sex, 

 and that the factor for color-blindness is linked with 

 the determiner for sex. Sex-linked inheritance, as 

 shown in this case, may be illustrated by the diagram 

 above (Fig. 87) in which, for the sake of simplicity, 

 only sex chromosomes and the determiners for color- 



