Genetics of inbred Drosophila melanogaster XII. Effects of an X-chromosome inversion on primary and secondary non-disjunction

Abstract

Luning., K. G., Lake, S. and Linde, M. 1984. Genetics of inbred Drosophila melanogaster XII. Effects of an X-chromosome inversion on primary and secondary non-disjunction.—-Hereditas 100: 247–257. Lund, Sweden. ISSN 0018–0661. Received August 1, 1983 In an inbred line of Drosophila melanogaster. Oregon (code 2), an inversion covering the proximal half of the X-chromosome was induced (symbol: In(l) Lu-l y wd cxvf-2). It has been shown that inversion homozygotes have low frequencies of primary nun-disjunction. in the same manner as equilinear females with regular gene order of the 2–line. Intra-strain structural heterozygotes gave an excess of XO exceptionals but also a 5–fold increase of true primary non-disjunction (XXY) as compared to structural hornozygotes. Inter-strain crosses with mothers from line “K” revealed an influence both by the maternal genome and by the origin of the cytoplasm. Tests of secondary non-disjunction in structural heterozygous XXY females from both intra- and inter-strain crosses indicated highly complicated relations. When the mothers were of “2” origin the first brood showed lower frequencies of XXY exceptionals than in successive broods. whereas when the mother was of “K” origin there was a decrease after the 3rd brood (7th day). The “K”-line showed a dominance effect which was manifested by higher frequencies of XXY exceptionals. In regular daughters the Y-chromosome followed preferentially the proximal part of the X-chromosome of “K”. origin. There was no preference in the Y-chromosome distribution in intra-strain hybrids. There was a pronounced low frequency of recombinants among exceptionals. This indicates that the high frequencies of exceptionals from inversion heterozygous XXY females occur by another mechanism than in equilinear XXY females with the same genetic background.