242 



HEREDITY AND SEX 



substitute white eyes for haemophilia, the scheme 

 already given for white versus red eyes in flies applies 

 to this case. If, for instance, the mother with normal 

 eyes has two X chromosomes (Fig. 114), and the fac- 

 tor for haemophilia is carried by the single X in the 

 male (black X of diagram), the daughter will have 

 one affected X (and in consequence will transmit the 

 factor), but also one normal X which gives normal 



OrD 



OtD O OtD 



6 6 6 



6 6 



Fig. 116. — Pedigree of Ichthyosis from Bramwell. (After Davenport.) 



vision. The sons will all be normal, since they 

 get the X chromosomes from their mother. In the 

 next generation, as shown in the diagram (third line), 

 four classes arise, normal females, hybrid females, normal 

 males, and haemophilious males. Color blindness fol- 

 lows the same scheme, as the above diagrams illustrate 

 (Figs. 114 and 115). In the first diagram the color- 

 blind male is represented by a black eye ; the normal 

 female by an eye without color. The offspring from 



