The Cellular Basis 185 



determiner for color blindness and if any of those receiving this 

 determiner are males they will be color blind. Consequently we 

 have the curious phenomenon of simplex color blindness appear- 

 ing only in males and being transmitted to them only through ap- 

 parently normal females. 



On the other hand if a female is color blind she has inherited it 

 from both father and mother, i.e., the character in her is duplex, 

 and in all of her children by a normal male the character will be 

 simplex; accordingly all of her sons will be color blind and all of 

 her daughters will be normal, though carrying the simplex deter- 

 miner for color blindness. 



Sex-linked Lethal Factors. One of the most interesting cases 

 of linkage is found where early death is linked with sex. In 

 Drosophila a considerable number of lethal mutant factors have 

 been demonstrated in the X chromosome and all individuals in 

 which such a factor is not balanced by a normal allelomorph die 

 early. All males that receive such a lethal die, since there is only 



Chromosomes 



Y? /rh VV 



z^y A A Parents 



I XI r | Gametes 



Gametes 



XX XO XO v* 



c? c? ?$<?<? 



FIG. 64. DIGARAM OF INHERITANCE OF COLOR BLINDNESS THROUGH THE 

 FEMALE. A color blind female transmits her defects to all her sons, to 

 half of her granddaughters and to half of her grandsons. Corresponding 

 distribution of sex chromosomes on right. (After Morgan.) 



