Der Faktore ^ug beiDrosophila Melanogaster: Lokalisation, Frequenzänderungen in Massenzuchten und Lebensleistungen Seiner Träger im Vergleich mit einem Wildstamm

Abstract

A factor causing dark pigmentation of the abdomen in females ofD. melanogaster has been located on the third chromosome, at locus69,8±0,4 morgans.

Among 19,050 flies no crossing over was found to occur between this factor (derived from a wild population) and the geneebony. These results and those of segregation experiments point toward an allelism of the dark factor withebony. For the dark factor the symbole ^ug is used.

The compounde ^ug /e is phenotypically indistinguishable from dark individuals of genotypee ^ug/e ^ug.

In 12 mass cultures, thee ^ug allele formed a balanced polymorphism with the wild type allele. Up to the end of the experiments lasting eight months, the heterozygotes (e ^ug/+) were present in excess. The frequencies ofe ^ug/e ^ug-flies sank to the lowest value in the course of 8 weeks and thereafter remained (after a brief rise) at an almost constant level. In no case dide ^ug disappear from the populations. Varying experimental temperatures (20°, 25°, 28°C) had no effect whatever upon the selective processes, with the exception of an increase of dark females at 20°C.

The imagos of genotypese ^ug/e ^ug,e ^ug/+ and +/+ were compared with reference to fecundity, hatchability, viability of larvae and pupae, drought resistance, imaginal age attained, and sterility. The homozygous dark animals consistently show reduced vitality. Regarding fecundity, drought resistance, and imaginal age attained, heterosis effects could be demonstrated. The balanced polymorphism is explained by the relatively higher fitness of the heterozygotes.