272 HEREDITY AND ENVIRONMENT 



these characters are carried by the sex chromo- 

 somes and has named them seoo-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 



w 



(5 



Parents 



I >^ I ( Gametes 



X 2? 9 



2X} 



TXT " 



X IZ 9 j 



? C? (? 



Fi 



Gametes 



F2 



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

 $ and red-eyed <?; Fj, red-eyed J and white-eyed (J ("criss- 

 cross inheritance"); Fj, equal numbers of red-eyed 5 and J 

 and white-eyed J and ^. The distribution of the sex chromo- 

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



