SCARLET, IDENTICAL WITH SEX-LINKED VERMILION. 2O9 



then back crossed either to pinkoid or scarlet stock, as the case 

 might be. Males were used thus because there is no cros-ing 

 over in males in melanogaster. Pinkoid was found to be a second 

 chromosome gene as no star fly was pinkoid but all not-star 

 individuals were pinkoid without regard to whether or not they 

 were also dichaete. The pinkoid strain had a very low viability, 

 however, and was hard to keep going, so that it is not a satis- 

 factory character for use in genetic experiments. The strain 

 died out while efforts were being made to place the gene in the 

 second chromosome by its linkage to other second chromosome 

 genes. 



By a similar cross, scarlet was found to be in the third chromo- 

 some; as a star dichsete male, heterozygous for scarlet, back 

 crossed to a scarlet female produced dichaete flies which were 

 never scarlet, and not-dichaete flies which were always scarlet. 



Further tests were made to dichsete and to hairless in the 

 third chromosome by crossing scarlet to each and back crossing 

 the heterozygous hairless or dichaete females to pure scarlet 

 males. The results indicated that scarlet is to the left of dichaete 

 in the chromosome, though more extensive data should be ob- 

 tained. The counts from three cultures gave 534 non-crossovers 

 and 15 crossovers between dichaete and scarlet, or a percentage of 

 crossing-over of 2.7. Three cultures to test linkage to hairless 

 produced a total of 552 flies of which 140 were in crossover classes, 

 which gives a crossover value of 25.4 per cent. According to 

 unpublished data of Bridges and Goweh the crossover percentage 

 of dichaete and hairless is 18.6. The data here recorded indicate 

 that scarlet is to the left of dichaete, as scarlet gave a crossover 

 value of 25.4 from hairless and scarlet is not far enough from 

 dichaete to be to the right of hairless. However, the relative order 

 of scarlet and dichaete can be definitely settled by more data and 

 by using scarlet with two loci of known position simultaneously. 



SUMMARY. 



1. Scarlet is a new eye color identical in appearance with 

 vermilion but in the third chromosome. 



2. When scarlet is crossed to vermilion, normal red eyes result, 

 except where sons inherit vermilion from their mother. 



