yS Heredity and Eugenics 



and X, and those of the male are X-L and — , then the 

 following combinations should result: 



This expected result accords with that actually obtained 

 by Morgan. 



Color-blindness in man is a sex-limited character, the 

 inheritance of which resembles that of white eyes or short 

 wings in Drosophila, rather than of barring in poultry. 



Color-blindness is much commoner in men than in 

 women. A color-blind man, however, does not transmit 

 color-blindness to his sons, but only to his daughters, the 

 daughters, however, are themselves normal provided the 

 mother was; yet they transmit color-blindness to half 

 their sons. A color-blind daughter could be produced, 

 apparently, only by the marriage of a color-blind man with 

 a woman who transmitted color-blindness, since the daugh- 

 ter to be color-blind must have received the character from 

 both parents, whereas the color-blind son receives the charac- 

 ter only from his mother. 



Color-blindness is apparently due to a defect in the 

 germ cell — absence of something normally associated there 

 with an X-structure, which is represented twice in woman, 

 once in man. Color-blindness follows, therefore, in trans- 

 mission, the scheme show^n in Fig. 38, 



