CHAPTER VII 

 MULTIPLE ALLELOMORPHS 



The meaning of the term multiple allelomorphs 

 may be illustrated by the following example : 



1. If a white-eyed male of Drosophila is mated to 

 a red-eyed female, the F 2 ratio of 3 reds to 1 white is 

 explained by Mendel's law, on the basis that the 

 factor for red is the allelomorph of the factor for 

 white. 



2. If an eosin-eyed male is mated to a red-eyed 

 female, the F 2 ratio of 3 reds to 1 eosin is also ex- 

 plained if eosin and red are allelomorphs. 



3. If the same white-eyed male is bred to an eosin- 

 eyed female, the F 2 ratio of 3 eosins to 1 white is 

 again explained by making eosin and white allelo- 

 morphs. 



There are here three factors, any two of which 

 may meet, and whenever they do, they behave as 

 allelomorphs. They form a system of triple allelo- 

 morphs. 



On the chromosome hypothesis the explanation of 

 this relation is apparent. A mutant factor is located 

 at a definite point in a particular chromosome; its 

 normal allelomorph is supposed to occupy a corre- 

 sponding position (locus) in the homologous chromo- 

 some. If another mutation occurs at the same place, 



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