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THE POPULAR SCIENCE MONTHLY 



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Fig. 3. Diagram to show the pairs of chromosomes (a, c) and their behavior 

 at the time of maturation of the egg. Three pairs of chromosomes are represented ; 

 three from one parent, three from the other. The six possible modes of separation 

 of these three are shown in the lowest line. 



gets one of each kind of chromosome from one parent and one of each 

 kind from the other parent. At the maturation of the germ-cells the 

 maternal chromosomes and the paternal chromosomes come together in 

 pairs and appear to fuse (Fig. 3, d, e). They then separate, and after 

 two peculiar divisions one chromosome of each pair goes into the egg 

 and one into the polar body. Similarly for the sperm. There is no 

 evidence that all the maternal chromosomes go to one germ-cell, and all 

 the paternal to the other, more frequently than chance assortment calls 

 for, and we are free to suppose that a random assortment of chromo- 

 somes takes place, so that each egg and each sperm gets one of each 

 kind regardless of its parental origin (Fig. 3, lower line). 



With the acceptation of this view it appears at first sight that in a 

 given race there can not be more independent pairs of characters that 

 show assortment than there are pairs of chromosomes. Since the 

 number of chromosomes is fairly limited it might appear that we could 

 reasonably expect to make still more probable the chromosome hypoth- 

 esis by finding that the number of independent pairs of Mendelian 

 characters is not greater than the known number of chromosomes in a 

 given race ; or else we might expect to disprove the chromosome hypoth- 

 esis by showing that the number of independent pairs of characters does 



