ANOTHER CASE OF MULTIPLE ALLELOMORPHS IN 



DROSOPHILA. 



T. H. MORGAN. 



It has been shown 1 that the factor for white eye color and the 

 factor for eosin eye color are allelomorphs. Each arose as a 

 mutation, but unlike other original and independent muta- 

 tions they do not give, when crossed, the wild type (red eye) 

 by recombination. Each factor has the same normal allelo- 

 morph in the wild fly, and each factor gives the same linkage 

 ratio as the other one with any sex-linked factor. The factor 

 for eosin, the factor for white and their normal allelomorph 

 form a system of triple allelomorphs. Only two of these factors 

 can exist at any one time in the same female, and, since they are 

 sex-linked, only one at a time in a male. In consequence, a 

 red-eyed female may be heterozygous for white or for eosin, 

 but never for white and for eosin. 



Another similar case has also appeared. In certain crosses, 

 involving yellow body color, a yellowish male appeared that was 

 characterized by a light spot on the upper surface of the posterior 

 end of the abdomen (Figs. 3 and 4). When the yellow stock was 

 examined another male of the same kind was found there. It is 

 evident that in the first case the new type must have come from 

 the original yellow stock. The mutation probably occurred in 

 the stock one or more generations before it was discovered. 



It was natural to assume that such a peculiar spot could be 

 transferred to gray or to black flies. The original male and 

 later many of his offspring that bore the same character were 

 mated to gray and to black flies. The first generation was 

 always normal gray. In the second generation the yellows and 

 the yellow blacks ("browns") were spotted, but never any of 

 the gray or the black flies. Thinking that the spotting was 

 closely linked to the yellow factor and might cross over if enough 

 flies were bred I continued the experiment for four or five months. 



1 Morgan and Bridges, Journ. Exp. Zool., XV., 1913. 



