NO. 572] MULTIPLE ALLELOMORPHS 451 



After the publication of my own and of Sturtevant's 

 paper I set to work to obtain crucial evidence in favor 

 of, or opposed to, the view that yellow and gray are 

 allelomorphic. Little, also, it appears, lias carried out 

 some new experiments which he lias recently published, 

 with the results just stated. My own data have been 

 ready for some time, but I have withheld them in order to 

 get a sufficient body of evidence 1 to make the case con- 

 vincing, especially in the light of the possibility that the 

 crossing over might occur in one sex and not in the other. 

 For, if no crossing over occurred in the male, there 

 might be crossing over in the other sex, which would not 

 reveal itself unless the experiments were delil>«-i-;it ••]>" 

 planned so that both sexes are tested. This consideration 

 seems to have been overlooked by Little, for he has 

 omitted in his confirmatory paper to give the sexes of the 

 animals used. Without a knowledge of this relation even 

 his confirmation fails to confirm (as he supposes) the 

 view that he formerly combated. 



Since Miss Durham worked with common gray and I 

 with gray white-belly, and both are ' * repelled ' ' by yellow, 

 i. e., both are allelomorphs of yellow, it follows thai these 

 two grays are also allelomorphic to each other. 



The evidence that black belongs to the same series of 

 allelomorphs is obtained in the following way : If a given 

 yellow is mated to black, and yellow and gray offspring 

 are obtained, and if then the yellow offspring are mated 

 to black again and now give yellow and black only, the 

 proof is furnished; for in the first mating yellow and 

 agouti have repelled each other, and the yellow-bearing 

 gametes have united with the black gametes of the other 

 sex to give the yellow offspring. The second mating 

 shows that black is now repelled in turn by yellow and is 

 therefore allelomorphic. 



This may be illustrated in the following way: Let 

 B Y = yellow, b = black and B = gray. These three 

 factors may be treated as allelomorphs, then: 



