THEORY OF EVOLUTION 125 



In man there are several characters that show 

 exactly this same kind of inheritance. Color 

 blindness, or at least certain kinds of color 

 blindness, appear to follow the same scheme. A 

 color blind father transmits through his daugh- 

 ters his peculiarity to half of his grandsons, 

 but to none of his grand-daughters (fig. 38 A) . 



? * 



Diploid Nuclei XX XO 



Gametes X X X 

 Fertilization 



Zygotes XX XO 



FIG. 60. Diagram of sex determination in type with XX 

 female and XO male (after Wilson). 



The result is the same as in the case of the white 

 eyed male of Drosophila. Color blind women 

 are rather unusual, which is expected from the 

 method of inheritance of this character, but in 

 the few known cases where such color blind 

 women have married normal husbands the sons 

 have inherited the peculiarity from the mother 

 (fig. 38B) . Here again the result is the same 

 as for the similar combination in Drosophila. 



