I 

 n 



I . / . I I / 



Jr--i 2 



n- n- N- Nn 



THE CCCLRRENCE OF COLOR BLINDNESS IN ONE FAMILY 



The above diagram illustrates the history of color-blindness as it occurred in three successive 

 §;eneraticns. Th.e father was color blind, and the impediment was inherited by his son and 

 cne daughter. The mother and one daughter had perfect eye-sight. The daughter who was 

 color blind had two sons, both with imperfect eyesight. The son also had two children, a 

 bo}^ and a girl, who both, like their mother, b.ad normal color vision. (Fig. 12.) 



tioned. For the males this is of course 

 simple, since it may be known from 

 the phenotype. all normal males (IV 3) 

 being N — and the color blind ones 

 /,— (II 1. 3; III 3; IV 1. 2). In the 

 case of the normal females, on the other 

 liand, the genotype must be ascertained 

 from the known kin. The subject's 

 mother (II 2), for example, was nor- 

 mal, but since she had both a color 

 blind son and daughter she must have 

 been Nn, that is, a "carrier" of color 

 blindness ; the son must have inherited 

 the color blindness from his mother, 



since it is transmitted only in that way, 

 and a daughter can be color blind only 

 when she inherits it from both parents. 

 The other daughter (III 5) was nor- 

 mal, but must have been heterozygous 

 (Nil) because of her father being color 

 blind. The same rule applies to the sub- 

 ject's own daughter (IV 4). The only 

 other woman described is the subject's 

 wife (III 4), who had normal vision, 

 and who probably was homozygous 

 (NN), for had she been heterozygous 

 the chances would have been even for 

 either the son or the daughter to be 



