140 THEORY OF EVOLUTION 



there are three sex chromosomes X X Y 

 wliich are homologous in the sense that in nor- 

 mal individuals the two present are mates 

 and separate at the reduction division. If in 

 the X X Y individual X and X conjugate and 

 separate at reduction and the unmated Y is free 

 to move to either j^ole of the spindle, two kinds 

 of mature eggs will result, viz., X and XY. 

 If, on the other hand, X and Y conjugate and 



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Fig. 69. Figure of the chromosome group of an XXY 

 female, that gives non-disjunction. 



separate at reduction and the remaining X is 

 free to go to either pole, four kinds of eggs will 

 result — XY — X — XX — Y. As a total result 

 four kinds of eggs are expected: viz. many 

 XY and X eggs and a few XX and Y eggs. 



These four kinds of eggs may be fertilized 

 either by female-producing sperms or male- 



