214 



GENETICS 



sex or the other. They are, therefore, well described 

 by the term *' sex-limited." 



(1) Color-blindness 



This phenomenon may be illustrated by the in- 

 heritance of human color-blindness, a character which 

 appears to be linked with the determiner for sex. It 

 requires a duplex, or homozygous, dose of the deter- 

 miner for color-blindness to produce a color-blind 

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



Gametes (x 



f: 90 9@ 



Fig. 65. — General diagram for sex-limited inheritance. The underscored 

 symbol (21) 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 



