THE DETERMINATION OF SEX 215 



sex, and that the factor for color-blindness is linked 

 with the determiner for sex. Sex-limited inheritance, 

 as shown in this case, may be illustrated by the dia- 

 gram on the opposite page (Fig. 65) in which, for the 

 sake of simplicity, only sex chromosomes and the de- 

 terminers for color-blindness are represented. Under- 

 scored x. represents a color-blind determiner linked 

 to a sex chromosome. 



From this diagram, which agrees substantially 

 with the facts, it is apparent that a color-blind male 

 mated to a normal female will produce no color-blind 

 offspring, although the females will be "carriers" 

 of color-blindness, that is, will possess the factor in 

 simplex form and will, therefore, carry it for the female 

 in a latent condition. 



The sons of such a mating having a normal mother 

 and a color-blind father will be absolutely free from 

 the defect and cannot produce color-blindness in any 

 of their offspring when mated with a normal strain. 

 If, however, the "carrier" daughters from such a 

 parentage, who are genotypically heterozygous for 

 color-blindness but phenotypically normal, mate with 

 normal individuals, the expectation is that one half 

 of the sons, and none of the daughters will be color- 

 blind, but that one half of these daughters will carry 

 the color-blind determiner in simplex form, that is, in 

 a condition ineffective for producing color-blindness 

 in female individuals. 



All of the various possibilities in the inheritance of 

 color-blindness according to the sex-limited interpre- 

 tation are indicated in the following table : 



