282 



HEREDITY AND ENVIRONMENT 



known as Daltonism, in which the affected 

 person is unable to distinguish between red 

 and green. It is known that males are more 

 frequently affected than females, and that 

 color blindness is in some way associated with 

 sex. It requires two determiners for color 

 blindness, one from the father, the other from 

 the mother, to produce a color blind female, 

 whereas only a single determiner is necessary 



Chromosomes 

 X0 M Parents 



X 6 , 



I Xl \ Gametes 



1 J? 9 



2XH 

 9 



Fi 



(S 



<Q> <Q> <D> <•> 



? 9 j e 



9 



x n 



IX 



? 



+ Gametes 



F2 



6 6 



Fig. 61. Diagram of inheritance of color blindness through 

 the male. A color blind male (here black) transmits his 

 defect to his grandsons only. The corresponding distribution 

 of the sex chromosomes is shown on the right, the one carry- 

 ing the factor for color blindness being black. (After 

 Morgan.) 



