PHENOMENA OF INHERITANCE 277 



normal mother have only normal children, 

 but the father transmits to his daughters 

 and not to his sons the sex-determiner which 

 carries the factor for color blindness. But 

 since color blindness does not develop in fe- 

 males unless it is duplex {i.e. comes from both 

 father and mother) whereas it develops in 

 males if it is simplex {i.e. comes from either 

 parent) all the daughters of a color blind 



Chromosomes 



XX Parents 



(? 



Gametes 



Gametes 



<a> <m> <Q> <m> 



Fig. 62. Diagram of inheritance of color blindness through 

 the female. A color blind female transmits her defect to all 

 her sons, to half of her granddaughters and to half of her 

 grandsons. Corresponding distribution of sex chromosomes on 

 right. (After Morgan.) 



