EYE COLOR IN DROSOPHILA MELANOGASTER 



369 



TABLE 25 



The Fz offspring given by the Fi wild-type females and Fi eosin males, from the out- 

 cross of pinkish females to ivild males 



CREAM C 



While looking over the eosin stock (July 13, 1916) in search 

 of a virgin female, I noticed that a few of the flies seemed to be 

 unusually light in eye color. If this paleness were of genetic 

 origin, then the gene must be of recent mutation, for on two 

 occasions subsequent to the discovery of creams whose origin 

 might be traced back to the eosin stock, this stock had been bred 

 in such a way as to make it extremely unlikely that any cream or 

 other eye-color mutation then present could fail to be eliininated. 



A pale eye color due to a mutation within the eosin stock 

 might be an allelomorph of eosin, a specific modifier of eosin, or 

 a non-specific modifier, such as vermilion or pink. The gene 

 for the modifier might be sex-linked or be in any of the other 

 three chromosomes. Only one experiment was carried out with 

 this pale eye color, but this experiment was so planned that it 

 answered all the above points. One of the pale females was 

 mated to a star dichaete male. The Fi offspring showed at 

 once that the pale color was due neither to an allelomorph of 

 eosin nor to a sex-linked modifier, for the sons were all standard 

 eosin in eye color. Likewise the color was a strict recessive, 

 both in eosin (the sons) and in red (the daughters). 



For the production of F2, Fi wild-type females and Fi eosin 

 star dichaete males were mated together. The first point ob- 

 served in F2 was that the gene produced no visible effect by itself, 

 for in that half of the offspring that were not-eosin none of the 



