In Drosophila, vitellogenins (yolk protein precursors) are synthesized by the female fat body, secreted into the hemolymph and subsequently taken up by the developing oocytes. The male fat body, on the other hand, does not do this even when immature ovaries are transplanted into the body cavity and grow. Thus, the hemolymph vitellogenins serve as an easily detectable sexually dimorphic biochemical marker.--We have examined hemolymph vitellogenins by SDS polyacrylamide gel electrophoresis in flies carrying various sex-transformation mutants (dsx, tra, tra-2 and tra-2OTF) singly and in all possible combinations. Chromosomal females homozygous for tra or tra-2 have no detectable hemolymph vitellogenins, while those homozygous for tra-2OTF exhibit appreciable levels of these proteins. Flies homozygous for dsx, both X/X and X/Y, have hemolymph vitellogenins, although the amount is consistently smaller in the latter. Indeed, X/Y; dsx/dsx is the only genotype in which hemolymph vitellogenins are detected in the X/Y flies. A clear hierarchy of epistasis exists among these sex-transformation mutants when they are examined in various combinations: dsx greater than tra, tra-2 greater than tra-2OTF. Moreover, an interaction between tra-2OTF and tra was seen in these experiments: X/X; tra-2OTF/tra-2OTF flies show the presence of only a trace of hemolymph vitellogenins when they are made heterozygous for tra. These results, combined with observations on gonad morphology, are discussed with respect to the Baker and Ridge (1980) hypothesis of sex determination.

Animals↗

PubMedDate not supplied

A sex-transformation gene in Drosophila melanogaster.

A sex-transformation gene, tra-2OTF, of Drosophila melanogaster is described. The gene is an allele of tra-2 (transformer-2, 7--70+/-), acts only on XX individuals and transforms them into morphologically nearly normal but sterile males. Neither a male-specific lethal gene mle nor the male-killing maternally transmitted infectious SR-agent have any effect on the tra-2OTF transformed flies. External as well as internal reproductive organs of tra-2OTF transformed flies, except for the gonads, are male. The gonads, which are yellowish-colored rudimentary testis-like structures in tra-2 transformed flies, are rudimentary ovaries without yellowish coloration that sometimes develop to near maturity. Numbers of bristles in each of the female pattern in tra-2OTF and tra-2OTF/tra-2 transformed flies, while these bristles are of the male pattern in tra-2 transformed flies. Furthermore, the sixth abdominal sternite, which in normal males as well as in tra-2 transformed males lacks bristles, bears numbers of bristles in tra-2OTF and tra-2OTF/tra-2 transformed flies.

Animals↗