EYE COLOR IN DROSOPHILA MELANOGASTER 



359 



If the high value of culture 2777 were not due to a homozygous 

 not-Ci„ condition, then it should be due to the converse cause — 

 homozygosity for C„, ; that is, the eosin stock which had fur- 

 nished the other parent for our original experiment had itself 

 been carrying the linkage variation Cm. In this case every 

 cream III ebony fly from the high- value culture should be homo- 

 zygous for C,ii, and should give, when outcrossed to eosin flies 

 free from Cm, all offspring heterozygous for Cm and all daughters 



TABLE 17 



The B. C. (Fz) offspring given by continued breeding from a low crossover value line 



(2773) of table 16 



giving the low value. One such test was made and the daughters 

 all showed the low value (table 18). 



Both of these tests (tables 17 and 18) pointed to the presence 

 of Cm in the particular eosin stock used to outcross to, though 

 they were not conclusive because of being done on so small a 

 scale. Conclusive proof (in press, Carnegie Publication no. 287) 

 was soon furnished by Sturtevant, who had been trying for some 

 time to get, by crossing over a stock, which should be Cm but not 



