OF MUTANT CHARACTERS. 



275 



between nick and vestigial. The possil)ility of this ronneofion wan 

 strengthened by the fact that one other back-cross culture ('2:V2S) had 

 given black nick in about the same frequency as hiui the (jthcr two, 

 but the remaining blacks were here vestigkil instead of simply bhick! 



Table 123.— Pi, black nick d" X star 9; B.C., F, .^^tar female X black nick 



{black vestigial <^ in case of 246 L 



The italicized numbers refer to vestigial. 



In the next generation, made from star females and black nick 

 males (from 2329), there was one culture giving black nicks and l)lack8 

 (2422), and one giving black nicks and black vestigials (24 IG). 



VESTIGIAL-NICK COMPOUND. 



It was now realized that probably not one of the nicks had failctl to 

 be heterozygous for vestigial, and it was suspected that the prescMice 

 of vestigial might be a necessary condition for the development of the 

 nick character. It was concluded that the mutant "nick" might be 

 an allelomorph of vestigial, which by itself gave no visible difference 

 from the wild-type (most of the many black not-nicks being homozy- 

 gous for the mutant gene), but which gave the visible character "nick " 

 when compounded with vestigial 



(-ir) 



The original male was by inference black vestigial in one second 

 chromosome and black nick in the other. One of the Fi flics Imd car- 

 ried the black nick second chromosome and a wild second chromosome, 

 while the other carried the black vestigial second chromosome and a 

 wild-type second chromosome. The Fo culture shoukl then give 3 

 wild-type flies to 1 fly that would be a vestigial-nick compound and 

 would show the nick character. 



The second set of F2 cultures gave one precisely like the first and 

 one which gave no nick whatever, but instead gave vestigials. In tiiis 

 case both Fi flies were of the type that received the black \(>siigi;d 

 second chromosome of the black nick father. 



