136 PHYSICAL BASIS OF HEREDITY 



lined genes, which must, however, if carried by the sex- 

 chromosomes, be linked to each other. The number of 

 chromosome pairs in man is, according to Guyer, 12 (Fig. 

 55, c), but Wiuewarter describes 24 pairs (Fig. 55, d). 

 The difference would seem to be due to technic, rather 

 than to differences in different races of men. 



)l- II. He IL 



lie II, IL ^» 



? I «• 



ni 



r\t J *AI 



Fig. 54. — Types of chromosome groups found in Drosophila. A-H female groups; 

 I-L female and male groups. In A, C, F, I, J, K, and L, the X-chromosome can be identi- 

 fied, because, in the male (Alex. Metz), the Y-chromosome has a different shape from the X. 



It should be emphasized that it is to be expected for 

 new types that the number of characters that may seem 

 to give independent assortment will be found at first 

 greater than the number of chromosomes, because wher- 

 ever two genes in the same chromosome are far apart they 

 will appear to assort independently until the discovery 



