Genetics of inbred Drosophila melanogaster

Abstract

In two inbred lines of Drosophila melanogaster, marker genes had been induced (y, wa, ex, v and f in Oregon, code “2”; and w in Karsnäs, code “K”). As well as the two original lines, two derived lines with mutual exchange of cytoplasm and genome were obtained by more than 40 generations of back-crossing of reciprocal hybrids to males from the paternal line. Both XX and XXBsYy + females were available from the four lines. Isogenic hybrids with mothers from the two original and the two derived lines were tested for recombination in the y-cx-v-f regions. Simultaneous comparisons were made between hybrids from XX mothers and both XX and XXY daughters of XXY mothers. There was no difference between the two groups of XX females. In the distal region, y-ex, there was in all tests an increasing frequency of recombination over successive broods with the pattern influenced by the maternal genotype, the origin of the cytoplasm and the presence of an extra Y-chromosome. The median region, cx-v, showed a tendency towards decreasing recombination, with some influence exerted by the cytoplasm. The sub-proximal region, v-f, showed a slight tendency towards decreasing frequencies, in early broods related to the maternal genotype. The XXY females had lower frequencies than XX females. – It was shown that the Y-chromosome in XXY hybrids had, in all four combinations, a tendency to be included in the same nucleus as the centromere of the “K”-line more often than randomly. The similarity in the increasing frequency of recombination in the distal region, y-ex, in regular and secondary non-disjunction exceptionals as well as the decreasing frequencies of both recombination in the v-f region in XXY females and secondary non-disjunction are discussed.