A SEARCH FOR ADDITIONAL X-LINKED GENES AFFECTING SEX DETERMINATION INDROSOPHILA-MELANOGASTER

The gene Sex-lethal (Sxl) plays a pivotal role in Drosophila sexual de velopment. Once activated in response to the X:A ratio signal in XX em bryos, Sri participates in appropriate implementation of all known asp ects of sexual differentiation. We have attempted to identify new X-li nked genes involved in sex determination, especially those involved in the regulation of Sri. Since misregulation of Sri, or that of the gen es that regulate it, leads to female-specific lethality, or synergisti c female-lethal gene interactions, or both, we used these criteria to screen about 10,000 EMS-treated chromosomes for (i) recessive female-s pecific lethality or (ii) enhanced female lethality in transheterozygo us combination with Sri. Four potentially useful mutations-Sxl(dlf), f l-35, fl-46, l-43-were recovered and a few of their properties were ch aracterized. Approximate map positions of these mutations were determi ned by meiotic mapping. To understand their probable position(s) in th e hierarchy of genes regulating sex determination, we studied dose-dep endent interactions between them and mutations in genes known to affec t sex determination by generating double and triple heterozygotes. The se studies suggest that (i) Sxl(dlf) is not defective in the 'early' r egulation or functions of Sri, and (ii)fl-35, fl-46 and l-43 are unlik ely to be a part of the X:A ratio signal, i.e. they are not needed for the transcriptional activation of Sri. On the other hand, they could be affecting post-transcriptional processing of Sri transcripts.