EYE COLOR IN DROSOPHILA MELANOGASTER 



355 



From the cream males and females of culture 136 a pure stock of 

 the double recessive eosin cream was made up. This double 

 recessive will usually be referred to simply as cream, and 'not- 

 eosin' will be used in other cases. 



In order to find out in which chromosome the gene of this 

 cream lies, a second cream female (found February 28 in the 

 same culture as the first) was mated to an eosin black male of 

 the stock which had been made up to test cream II. Two Fi 

 pairs (eosin 9 x eosin cf ) gave a 9: 3: 3: 1 ratio (table 13), 

 which proves that the gene for this cream is not in the second 

 chromosome. 



TABLE 13 



The Fi and F-i offspring from the outcross of a cream III female to an eosin 



black male 



The fact that this cream is not in chromosome II makes it 

 probable that it is in chromosome III, since chromosome IV is 

 very small. To test this point a cream female from the pure 

 stock made from culture 136 was mated to an eosin ebony male 

 from the stock which had been used in testing cream II. Three 

 pairs of eosin Fi flies gave the approximation to a 2: 1 : 1 : ratio 

 observed in table 14. 



The absence of the double recessive cream ebony proved that 

 this cream was in chromosome III, and it was accordingly called 

 cream III; the Roman III being the symbol for the third 

 chromosome. 



It was decided to find approximately the locus of cream III 

 in the third chromosome. To do this it was necessary to find 



