154 OTTO L. MOEIK 



seen from the Tnblo, (Table 4), 2 cross-overs between cf and the new- 

 gene were obtained in a total of 341 males, which gives 0,6 % of crossing- 

 over between these loci. The constitution of the male cross-overs prove 

 that the new mutant gene is located to the right of cut. Its locus 

 is accordingly, based on this test, at 20,6, which is in perfect accor- 

 dance with the locus of the old singed gene, (at 20,9). 



Among the characteristics of the old singed mutant is also a 

 complete sterility of the homozygous singed females (Mohr, 1922). 

 This sterility is due to a defective condition of the eggs, which is 

 accompanied by a constant change in their form. It was therefore 

 expected that the females homozygous for the new singed gene would 

 likewise be sterile. When such females were crossed to new singed 

 or to unrelated males they proved, however, in striking contrast to the 

 old singed females, to be of normal fertility. Thus, for instance, a 

 mating of a homozygous new singed female to wild-type males gave 

 112 wild-type daughters and 102 singed sons (C. 2739). And a pure 

 stock could be maintained unselected without any difficulty. 



It was of interest to see, whether the eggs of the homozygous 

 new^ singed females showed any somatic alteration, and two such 

 females were therefore crossed to new singed and to wild-type males 

 respectively, and isolated in glass tubes with banana-agar culture 

 media. On the following day one of these females had laid 10, the 

 other 7 eggs, which on careful examination were found to be normal 

 in every respect. 



When this striking difference between the old singed and the new 

 singed gene, which both cause the same external character change, 

 had been detected, it seemed of importance to ascertain, whether the 

 old singed-new singed female compound was sterile or not. Females, 

 which carried the old singed and the fused gene in one X and 

 the new^ singed gene in the other were therefore crossed to wild-type 

 and to new singed males respectively, and it w^as found that the 

 compound was of normal fertility. Thus, the latter cross gave 29 singed 

 females; 23 singed fused and 17 singed males (C. 2768). An examina- 

 tion of the eggs, like the one mentioned above, was also in this case 

 carried out. Two compound females, which were brought into sepa- 

 rate test tubes, had on the following day laid 12 and 17 eggs respec- 

 tively, all of which were perfectly normal. 



Thus, in spile of the fact that the old and the new singed mutants 

 externally looked entirely alike, it was nevertheless clear from the 

 fertility tests of the females, that they were not identical, but only 



