272 



HEREDITY AND ENVIRONMENT 



these characters are carried by the sex chromo- 

 somes and has named them sex-linked charac- 

 ters. In the fruit fly, Drosophila,, he has 

 discovered more than twenty-five such charac- 

 ters, applying to the color of the eyes and of 

 the body, to the length of the wings, etc. A 

 typical case is shown in Figs. 59 and 60. The 

 eye color of this fly is normally red, but muta- 



Flies 



Chromosomes 



Parents 



_ 



Gametes 



FIG. 60. Reciprocal cross of Fig. 61. Parents, white-eyed 

 $ and red-eyed ^; F,, red-eyed $ and white-eyed ^ ("criss- 

 cross inheritance" ) ; F 2 , equal numbers of red-eyed 5 and <$ 

 and white-eyed 5 and g. The distribution of the sex chromo- 

 somes is shown on the right, as in Fig. 59. 



