The effect of sexcombless in genetic mosaics of Drosophila melanogaster

Abstract

Gynandric basitarsi possessing areas heterozygous for the sexlinked mutant sexcombless (sx) and hemizygous for it, and mosaic basitarsi possessingsx/+,sx/sx and +/+ areas have been studied for the developmental expression of sx and sx/sx patches in the sex comb region. The mosaic basitarsi were obtained as the result of somatic crossing over following X-ray exposure of larvae. In order to observe the sex comb-forming potencies in these XX tissues the flies had been made homozygous for the genetra which transforms females into phenotypic males. The development of sx/+;tra/tra females is greatly prolonged over that of normal females. Five of the 63 gynandric and two of the 39 radiation-induced mosaics showed a single typical tooth, a sixth gynandric basitarsus had two teeth. In all other cases intermediate bristles, or macrochaetae, or both, have been found iny sn sx hemizygous or homozygous patches irrespective of their size. The sx-initiated distortion of bristle arrangement found in non-mosaicsx male basitarsi has also been seen in many mosaic patches. The mutant genesx acts autonomously and interferes with the process of seta-cell to tooth determination at a relatively early stage in development of a bristle organ.