HUMAN INHERITANCE 189 



be due to one gene; or whether there are several 

 genes that differ in the degree to which they produce 

 the defect. We know of a good many cases in other 

 animals where there are several mutations of the 

 same gene. For instance, in Drosophila there is a 



I? 



XYc/ 



Fig. 70. — The designations as in fig. 69. Here a color-blind 

 woman mates with a normal male. All of her sons are color-blind, 

 her daughters have normal vision (but carry a factor for color- 

 blindness). In the F.^ generation, half the daughters and half the 

 sons have normal eyes and half are color-blind. 



series of ten such multiple allelomorphs for eye 

 colors that range from pure white to deejD wine-red. 



There is still another possible interpretation of 

 the different kinds of color-blindness — one which 

 a priori would seem to be the most probable — 



