INHERITANCE IN ORGANISMS 



567 



without an a:-chromosome unites with an egg cell, the zygote will contain 

 only one x-chromosome and will be male. In case the male possesses 

 both an x-chromosome and a ^/-chromosome, then the a:-chromosome 

 goes one way and the ^/-chromosome the other, and the result is that 



Formulc^ 6 =8+'x. 



Primary 

 Spermatocyte 



Formula 9=8+2x 



Sv Primary 

 Oocyte 



Two kinds ofsperm^ ^^L^^ ^ 

 Proc/uces 



Formu/a 6 = 8-*-2x 



One /<ino/ of egg cell 



Formula 9 = S+^x, 



Primary /^,. 

 Spermatocyte yil!( 



B 



Produces 



Formu/cf (^ = 8 + x-f-y Formu/a 9= 8^-2 x 



Primary .. 

 Spermatocyte^ 



Two /<.inds x> 

 Produces 9 



This may be reversed as in the case of A and B 



Fig. 390. — Diagrams illustrating sex determination in three different cases. 



there are again two types of sperm cells. If the sperm cell containing the 

 a;-chromosome unites with the egg cell also containing an a;-chromosome, 

 a female is produced; but if the sperm cell containing the ^/-chromosome 

 unites with an egg cell, then a male is produced, with both an rc-chromo- 

 some and a ^-chromosome. 



In other cases instead of there being two kinds of sperm cells there are 

 two kinds of egg cells. In fowls and in moths females have either one 



