MENDELIAN SEGREGATION 



15 



separation of the X chromosomes in the female there is 

 one X chromosome left in each egg. In the male there 

 is one X chromosome and another chromosome, its 

 mate, called the Y chromosome. Hence in the male 

 there are two classes of spermatozoa : one containing 

 X, the other Y. If a Y-bearing spermatozoon should 



FEMALE 



89 



MALE 



EGG 



SPERM 



CSD C5t^ 



Gametes 



98 



FEMALE 



9ff 



MALE 



Fig. S.— Diagram to slunv the history of the sex chromosomes from 



one generation to the next. 



fertilize an egg the result will be an XY individual, 

 or male. It is evident that the Y chromosome is 

 found only in the males, while an X chromosome 

 passes not only from female to female, but also from 

 female to male and from male to female. 



As will be shown now, certain factors follow the 

 distribution of the X chromosomes luid are there- 



