CORRESPONDING GENES IN DROSOPHILA. 57 



to compare the maps in more detail. The three loci concerned, 

 already well known in melanogaster, are sepia, hairless, and 

 claret. In the cases of sepia and claret the mutant types of 

 simulans are closely similar in appearance to the types of the 

 same names in melanogaster, and it was a simple matter to obtain 

 sepia hybrids and claret hybrids by crossing the types concerned. 

 The evidence that these are corresponding genes is thus of the 

 same nature as in the cases of scarlet, peach, and the sex-linked 

 genes previously reported (Sturtevant, 19210, b). 



Hairless is, however, dominant in both species, so that the 

 same difficulty was encountered here as in the case of delta 

 the hybrids show the mutant character even when it is introduced 

 from only one parent. But in each species hairless, like delta, 

 is lethal when homozygous; accordingly this lethal effect was 

 used to test the correspondence of the hairless genes. Since 

 the earlier tests of delta were not as clear-cut as might be desired, 

 the new tests were carried out with flies containing both genes, 

 and served to show that both loci correspond. 



D. melanogaster females that were A/H i.e., carried delta 

 in one third chromosome and hairless in the other one were 

 crossed to simulans males that were also A/H. There resulted 

 169 hybrid offspring: 164 delta hairless, 4 delta, I hairless, o 

 wild-type. If the delta genes do not correspond, so that A/A is 

 viable, the cross should give half as many delta flies as delta 

 hairless; if the hairless genes do not correspond, the hairless 

 class should also be half as large as the delta hairless class. The 

 few delta and hairless offspring produced are evidently due to 

 crossing over in the mothers, 1.5 per cent, of whose eggs are 

 expected to carry neither A nor H. The result was checked by 

 crossing melanogaster females that were AH/+ by simulans 

 males that were A/H. From this cross, all the AH eggs should 

 give inviable zygotes, and equal numbers of delta and hairless 

 offspring should result. There were obtained the following 

 hybrids: I delta hairless, 225 delta, 226 hairless, o wild-type. 

 The one delta hairless remains unexplained, for in this case the 

 mothers carried C m , which should have prevented all crossing 

 over between A and H. This individual probably represents a 

 new mutation, though it is possible that it was really homozygous 



