164 MULTIPLE ALLELOMORPHS 



native views of identical loci and of complete linkage 

 the method of origin of the mutant allelomorph is a 

 matter of prime importance. Emerson has described 

 one type (^'variegated" corn) in which a mutation 

 (to red) occurs frequently. This mutation is of 

 such a sort, as Emerson points out, that, on the 

 theory of complete linkage, it must involve the muta- 

 tion of two factors at the same time. On the theory 

 of multiple allelomorphs only one mutation is 

 necessary each time the change occurs. Fortunately 

 we have complete information concerning the origin 

 of the types of Drosophila that fall into this category. 

 One of these may now be given in detail before 

 attempting to decide between the claims of the rival 

 explanations. 



In 1911 a few males with white eyes arose in a 

 culture of red eyed flies. From them the stock of 

 white eyed flies was obtained by the usual procedure. 

 In 1912, in a culture of w^hite eyed flies having also 

 miniature wings and black body color, a male ap- 

 peared that had eosin eyes. He also had miniature 

 wings and black body color, so that there could be no 

 question of his origin from this particular stock. 

 The eosin stock is descended from this male. 



In 1913, in a cross between vermilion eyed flies and 

 wild flies several males appeared in F2 whose eyes 

 were quite different from vermilion. Analysis of 

 the case showed that a mutation had taken place in 

 the stock having vermilion eye color. The new color 

 proved to be a double recessive, for vermilion and 

 for a color called cherry. The new mutation had 



