168 MULTIPLE ALLELOMORPHS 



probable for the cases known than is that of complete 

 linkage (in the sense defined) . No one of the reasons 

 is in itself conclusive, but taken together they weight 

 the scales heavily on one side. 



1. When two mutants that depend on "multiple 

 allelomorphs" are crossed they give in Fi a type that 

 is like one or the other of the two mutants, or an 

 intermediate type. This type is scarcely ever like the 

 original (or wild) type. In this respect they differ 

 from other recessive mutant types which when 

 crossed together give the wild type. We understand 

 why in the latter cases the wild form is recovered. 

 It is because each mutant type contains besides its 

 mutant factor the normal (dominant) allelomorph 

 of the other type. Hence the original type is re- 

 constituted in the cross, as has been already stated. 

 But when two mutant allelomorphs occupying the 

 same locus are brought together neither of them 

 brings in the normal allelomorph of the other; 

 hence the wild type is not reconstituted. If the 

 cases in which these allelomorphic factors arose 

 independently are not cases of identical loci then the 

 explanation involves the occurrence of two muta- 

 tions at the same time, as explained in the case of 

 cherry. 



2. It is a characteristic of "multiple allelomorphs" 

 that the same character is affected. Nearness of 

 factors in the chromosome will not explain this fact 

 unless nearness means the same factorial basis, for 

 in the other mutants that we have obtained, nearness 

 of factors is in no way related to the kind of character 



