CHAPTER VII 



THE CORRESPONDENCE BETWEEN THE 



DISTRIBUTION OF THE CHROMOSOMES 



AND OF THE GENETIC FACTORS 



Attention has been called to the fact that paired 

 factors are distributed in the same way as are 

 homologous chromosomes, and that factors which 

 are assorted independently are distributed in the 

 same way as non-homologous chromosomes. In 

 proof of the latter point there is Wilson's evidence 

 for a Metapodius with three homologous m-chromo- 

 somes. It was found that the extra m goes to the 

 gamete that receives X as often as to the other 

 gamete. Miss Carothers describes in detail several 

 cases in the spermatogenesis of grasshoppers where 

 the distribution of chromosome pairs with unequal 

 members shows complete independence between 

 pairs. Not only are the pairs of factore assorted 

 independently, as are the chromosomes, but in 

 Drosophila, where the number of independently 

 assorting groups of factors has been determined, it 

 has been found that the number is identical with the 

 number of chromosome pairs. Moreover, even the 

 relative sizes of the groui:)s — ^bcth as determined by 

 the number of factors they contain and by the fre- 

 quency of crossing over witliin them — are the same 



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