CHANGE IN THE BAR GENE OF DROSOPHILA 305 



of her brothers and gave according to expectation both full-eye 

 and ultra-bar sons and ultra-bar and hel^erozygous daughters. 

 Other crosses followed expectation in a similar manner. 



That she is not the result of contamination is indicated, first, 

 by the fact that she is white-eyed, and that hypothesis therefore 

 necessitates contamination by a white full-eyed fly. Trap tests 

 showed that there were no such flies free in the laboratory, though 

 other kinds were caught. In the second place, only a single such 

 individual appeared. Thirdly, the fact that she is a heterozygote 

 makes it improbable that she is a stranger in the bottle. 

 Fourthly, the general laboratory procedure is the same as that 

 pursued when the reverse mutations of bar appeared, and the 

 arguments given for those cases by May (1917) hold in this case 

 also. 



Deficiency tests were made. If a piece of the chromosome 

 carrying the ultra-bar factor has dropped out, either the forked 

 gene which is —0.5 units from ultra-bar or the fused gene which 

 is +2.5 units away or both would in all probability be carried 

 with it. When full males derived from a cross of the mutant 

 female with ultra-bar males are mated with heterozygous fused 

 females, 'they should give fused sons if there is deficiency on the 

 plus side of ultra-bar. Such crosses gave no fused or forked sons 

 and deficiency cannot be considered as the explanation of the 

 mutant. 



Mutant B. In a cross between wild red-eyed females and a 

 22-facet white male from bottle no. 150 sp., 59 of the females 

 were heterozygotes according to expectation and there was one 

 full-eyed female. This exceptional female was crossed with wild 

 red males and gave 23 full-eyed females and 25 full-eyed males. 

 Both chromosomes therefore have the full-eyed factor, and the 

 case is not due to a failure of the ultra-bar factor to dominate. 

 Dr. A. H. Sturtevant has suggested that this may be a case of 

 non-disjunction. Unfortunately the eye color was not recorded 

 at the crucial point. 



Mutant C. A single full-eyed white male appeared in the 

 white ultra-bar stock no. 158.1 on December 26, 1917. It was 

 shown by test no. 291.1 to be like ordinary full-eye, but no further 

 tests were made. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 30, NO. 3 



