14 



MENDELIAN SEGREGATION 



mode of inheritance is explicable on the supposition 

 that it lies in the fourth pair of chromosomes. 



For an adequate understanding of the inheritance 



Fig. 7.— Normal eyes of Drosophila a, a'. Eyeless h-d; b, b' top and 

 side view of head of fly without eyes ; c, c' right and left eyes of another fly ; 

 d, small eye on right side, none on left. 



of factors in the first group it will be necessary to 

 consider the distribution of the sex chromosomes 

 (Fig. 8) . In the female of Drosophila there are two 

 X chromosomes (XX). After the conjugation and 



