l82 



Outline of Genetics 



somatic characters; but in addition there are extra 

 chromosomes that determine sex, known as sex chromo- 

 somes, or heterochromosomes . In this case the male con- 

 tains only one sex chromosome, while the female con- 

 tains two. At the reduction division, when the gametes 



MATURE INDIVIDUALS 



i 



OOOO 



o • o 

 oo oo 



oo oo 

 o» ^o 

 oooo 



Zygotes 



(This type of zygote (This type of zygote 



produces a male) produces a female) 



Fig. 28. — Illustrating behavior of sex chromosomes 



are formed, the chromosome equipment is reduced one- 

 half. It is obvious that in the female each egg receives 

 one sex chromosome, and therefore all eggs are alike in 

 this feature. In the male, however, with one sex chro- 

 mosome, at the reduction division the solitary sex chro- 

 mosome goes to one pole, leaving the other pole without 



