EYE COLOR IN DROSOPHILA MELANOGASTER 347 



DARK AND WHITING 



It was noticed (September 23, 1913) that in certain cultures 

 (m 100, M 101) which were part of the experiments on non-dis- 

 junction, there were present eosin males which were abnormally 

 dark in color. In the next generation more dark males appeared 

 and some of the white-eosin exceptional daughters were nearly as 

 dark as pure eosin females (no pure eosin females could occur in 

 this culture except by the very rare equational non-disjunction; 

 Bridges, '16). In subsequent generations the dark modification 

 continued to reappear in such manner and in such proportions as 

 to suggest that it was a converse case to that of cream a, that is, 

 that there was present a recessive gene, a specific darkener of 

 eosin, which does not modifj- the color of those flies which are not 

 eosin. No very extensive records of the behavior of dark were 



TABLE 6 

 The occurrence of whiting among the offspring of a pair of 'dark' eosin flies 



made, since my attention was soon diverted from this type by the 

 occurrence in the same cultures of a much more striking variation. 

 One of the dark females, supposed to be a white-eosin com- 

 pound, mated to a dark eosin brother gave a surprising result in 

 that there w^ere produced some females which were pm'e white in 

 eye color (table 6). "WTien these white females began to appear 

 they were set down as examples of equational non-disjunction, 

 but as the culture produced more and more of them it was seen 

 that they were appearing in far too great a proportion to be easily 

 explained by this rare phenomenon. Again, if the mother of ]\I67 

 were indeed heterozygous for the sex-linked white, then the white 

 sons should be equal to the eosin sons in number, instead of which 

 they were only about half as numerous. Furthermore, half of 

 the daughters should be pure eosin and half the lighter white- 

 eosin compound, while in fact they seemed aU to be pm'e eosin 



