ANOTHER CASE OF MULTIPLE ALLELOMORPHS. 



235 



able explanation is that a mutation backwards from spot to 

 yellow took place (with no change in the black). Another 

 interpretation is that contamination had occurred. This seems 

 highly improbable since at the time there was no stock of yellow 

 black in the laboratory, and only a few experiments under way 

 in which such individuals were being produced. Nevertheless, 

 so long as there were no other characters than these in the 

 experiment by means of which the offspring could be further 

 identified, I think that one cannot be too careful in interpreting 

 such rare occurrences as mutation backwards. A third possi- 

 bility is that a cross over occurred, and if so, spot is closely 

 linked to yellow, and crossed over only in this one case out of 

 the many thousands of cases. 



In order to see whether the spot would show in the female 

 of the "compound" yellow-spot, when the compound was also 

 black, a spot black female was bred to a yellow black male. All 

 the daughters were yellow black without trace of spot. The 

 sons were spot black. These mated together gave the following 

 F 2 generation. 



OTHER CROSSES WITH SPOT. 



We have another stock of black-colored flies called ebony 

 which belongs to our third group of factors. When spot female 

 was crossed to ebony male the daughters were gray and the sons 

 were spot. These inbred gave in 2 the following results. 



Gray. 



91 

 1 06 



Spot. 



102 



73 



Ebony. 

 29 



45 



Spot Ebony. 

 24 

 28 



The analysis is the same as in the case of spot by black. The 

 double recessive is spot ebony which has a brownish color differing 

 in tint from the brown of spot black. 



There is still another black-colored mutant called sable. It is 



