GENES IN RELATED SPECIES 



101 



sixteen normal genes are recessive to the dominant mu- 

 tant genes of the other species. 



Mutants of simulans have been mated to mutants of 

 melanogaster. In twenty cases tested, the mutant charac- 

 ter proved to be the same. 



10 



20 30 



40 



50 



60 



70 



80 



90 100 110 120 130 140 



H — Jr 



n 



t^v *$ ty 3p <ty 



KW — 1 1 ii \ +■ 



tfi 



I'll 



da 



se 



cu 





*> 



i !■■ --. 



4t 



-*-mel 



u lib 

 i — f— siml 



— H 



FTT&r- 



-m — 



-p*—- . 



^mel 



KP 



-*sim. 



Mg_ 



mel 



M 



sim. 



Fig. 59. 

 Chart showing, above, the corresponding loci of identical mutant 

 genes of the first or X-chromosome in Drosophila melanogaster and 

 in D. simulans, similarly, in the middle, of the second chromo- 

 some; and, at the bottom, of the third chromosome. (After Sturte- 

 vant.) 



This last result establishes the identity of the mutants 

 in the two types, and enables one to discover whether they 

 lie in the same linkage series, and in the same relative 

 position in each series. The chart (Fig. 59) shows by the 

 connecting dotted lines the relative position of the loci 

 of identical mutants so far worked out by Sturtevant. In 

 chromosome-I there is a remarkable agreement. In chro- 

 mosome-II only two identical loci have been determined. 

 In chromosome-III the agreement is not complete. It can 



