THE MECHANISM OF SEX-DETERMINATION 43 



When the egg sends off its two polar bodies, the chro- 

 mosomes divide or separate. At the first division seven 

 chromosomes pass out (C), and seven remain in the 

 egg. At the next division the seven chromosomes in 

 the egg divide again, seven pass out and seven remain 



Pro/en 



or 



9 



X 



••• 





• • 



A 



•3. 



in the egg (D). Of these seven, one chromosome, 

 recognizable by its large size, is the sex chromosome. 



All the eggs are alike (E). There is only one kind of 

 egg, but there are two kinds of sperm. Any egg that 

 is fertilized by a sperm carrying six chromosomes pro- 

 duces an individual with thirteen chromosomes. This 

 individual is a male. 



Any egg that is fertilized by a sperm carrying seven 



