GENETICS 171 



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divide as do the other chromosomes) must result in some sperm-cells 

 having an even number of chromosomes and others an odd number. 



For example, let us say there are 21 chromosomes in the original 

 germ-cell from which the sperm is to develop. One of the newly form- 

 ing sperm would possess ten and the other eleven chromosomes. The 

 regular somatic number of chromosomes in such an organism would be 

 twenty-two. The egg will, therefore, regularly divide and throw off 

 eleven to obtain the haploid number. Those eggs which are then fer- 

 tilized by a sperm containing ten chromosomes become males (as the 

 diploid number in such a case would again be twenty-one) and those 

 eggs fertilized by a sperm containing eleven would possess the full 

 somatic number of twenty-two chromosomes and become a female. 



This means that in those cases where there are X-chromosomes, 

 the odd chromosome never pairs in the maturation division with another 

 chromosome, nor does it produce a tetrad. It simply passes undivided 

 to the daughter sperm. 



References : 



L. Doncaster, "An Introduction to the Study of Cytology." 



W. E. Agar, "Cytology." 



W. E. Castle, "Genetics and Eugenics." 



East and Jones, "Inbreeding and Outbreeding." 



