EYE COLOR IN DROSOPHILA MELANOGASTER 341 



CREAM II 



Shortly after the discovery of the first cream (cream a) a second 

 cream appeared (September 15, 1913) among the eosin males and 

 females of a stock culture of lethal 2. Wild-type females heter- 

 ozygous for lethal 2 had been crossed to eosin miniature males, 

 and the Fi wild-type daughters again crossed to eosin miniature 

 males. The mothers of the culture which gave the creams were 

 therefore wild-type females heterozygous for eosin and miniature 



as well as lethal 2 ( ^ -^^, — ) while the fathers were eosin mini- 



\ +~i7^=r/ 



ature. The cream males and females which appeared were much 

 paler than cream a, though like cream a they were a light, trans- 

 lucent yellow with little or no pinkish tinge.^ None of the not- 

 eosin flies were different in color from normal red flies. 



A careful examination of the stock of eosin miniature failed to 

 show any flies that did not have the standard eosin ej^e color and 

 no lighter eye color has ever subsequently shown itself in this 

 stock. It is evident that the gene for the modification had been 

 present in the wild-type flies of the lethal 2 stock, but had been 

 unsuspected so long as eosin was not present as a base. The 

 demonstration that the cause of the observed dilution of eosin was 

 a gene behaving in inheritance like the other mutant genes was 

 easily made. 



One of these cream nlales was outcrossed to a wild female. 

 Among the F2 flies the creams reappeared, and, as in the parallel 

 case of cream a, the not-eosin flies were all indistinguishable from 

 one another and from wild flies in color. The F2 result resembled 

 that obtained with cream a, except that, as stated, the new cream 

 was considerably paler; and it was further discovered that be- 

 sides the creams approximately 50 per cent of the eosin males 

 were intermediates between eosin and this cream, that is, cream 

 II diluted eosin even in heterozygous form, so that the eosin sons 

 were visibly as well as genetically in the ratio 1 eosin : 2 eosin 



* Colored figures of the unmodified eosin, and of cream II, of cream b, and of 

 pinkish are being published by Bridges and Morgan in Carnegie Publication no. 



287. 



