No. 575] 



AN APTEROUS DROSOPI1ILA 



687 



like the apterous individuals than are any of the other 

 mutants, and since the two characters belong to the same 

 group the question arose as to whether or not the factor 

 responsible for one might be simply a modification of that 

 responsible for the other. Experiment V was performed 

 to determine this point. 



Long-winged flies heterozygous for apterous were 

 crossed with vestigial winged individuals, and F, and F 2 

 generations raised. The Fj flies were all long winged, 

 which fact in itself indicates the independence of the two 

 characters, for if they were allelomorphs either apterous 

 or vestigial should have appeared. In F 2 both vestigial 

 and apterous, as well as long-winged, flies appeared, 

 showing conclusively the independence of the two 

 characters. 



Summary of Experiments 



Experiments I and II show that the apterous character 

 is a simple Mendelian recessive, which independently 

 mendelizes with miniature wings, white eyes and ver- 

 milion eyes, and hence is not sex-linked (i. e., not a mem- 

 ber of Group I). 



Experiment III shows that the apterous factor is trans- 

 mitted independently of the factor for pink eye, thus indi- 

 cating that apterous is not a member of Group III. 



Experiment IV shows a linkage ratio to result from 

 crosses involving apterous and black, the ratio being such 

 as to indicate a very close linkage between apterous and 

 black, and to identify apterous as a member of Group II. 



Experiment V shows apterous to be distinct from ves- 

 tigial wing, to which it bears a considerable degree of 

 resemblance. 



Origin and Characteristics of the Apterous Mutant 

 The description of the apterous fly has been deferred 

 up to this point in order that it might be combined with a 

 discussion of the experimental results. 



The mutant has appeared upon several occasions, but 



