We have isolated about a thousandDrosophila P-element transposants that allow thein situ detection of genomic enhancer elements by a histochemical assay for β-galactosidase activity. We summarize the β-galactosidase staining patterns of over 200 such transposants in the adult. Our aim was to identify genes that are likely to be involved in the chemosensory and motor pathways ofDrosophila. Based on β-galactosidase expression patterns in the tissues of our interest, we have chosen some strains for further analysis. Behavioral tests on a subset of the transposants have, in addition, identified several strains defective in their chemosensory responses.

We studied the effect on female viability oftrans-heterozygous combinations of X-chromosome deficiencies andSxl^f1, a null allele ofSex-lethal. Twentyfive deficiencies, which together covered 80% of the X chromosome, were tested. Seven of thesetrans-hcterozygous combinations caused significant levels of female lethality. Two of the seven interacting deficiencies include the previously known sex determination genessans fills andsisterless-a. Four of the remaining uncover X-chromosomal regions that were not hitherto known to contain sex determination genes. These newly identified regions are defined by deficienciesDf(1)RA2 (7D10; 8A4-5),DJ(1)KA14 (7F1-2; 8C6),Df(1)C52 (8E; 9C-D) andDf(1)NI9 (17A1; 18A2). These four deficiencies were characterized further to determine whether it was the maternal or zygotic dosage that was primarily responsible for the observed lethality of female embryos,daughterless andextra macrochaetae, two known regulators ofSxl, influence the interaction of these deficiencies withSxl.

The geneSex-lethal (Sxl) plays a pivotal role inDrosophila sexual development. Once activated in response to the X: A ratio signal in XX embryos,Sxl participates in appropriate implementation of all known aspects of sexual differentiation. We have attempted to identify new X-linked genes involved in sex determination, especially those involved in the regulation ofSxl. Since misregulation ofSxl, or that of the genes that regulate it, leads to female-specific lethality, or synergistic female-lethal gene interactions, or both, we used these criteria to screen about 10,000 EMS-treated chromosomes for (i) recessive female-specific lethality or (ii) enhanced female lethality intransheterozygous combination withSxl. Four potentially useful mutations—Sxldlf, fl-35, fl-46, 1–43—were recovered and a few of their properties were characterized. Approximate map positions of these mutations were determined by meiotic mapping. To understand their probable position(s) in the hierarchy of genes regulating sex determination, we studied dose-dependent interactions between them and mutations in genes known to affect sex determination by generating double and triple heterozygotes. These studies suggest that (i)Sxldlf is not defective in the ‘early’ regulation or functions ofSxl, and (ii)fl-35, fl-46 and1–43 are unlikely to be a part of the X: A ratio signal, i.e. they are not needed for the transcriptional activation ofSxl. On the other hand, they could be affecting post-transcriptional processing ofSxl transcripts.

Hot water epilepsy (HWE) is a rare formof sensory epilepsy where seizures are precipitated by a stimulus of contact with hot water. While earlier studies have suggested causal role of genes for HWE, specific underpinnings are beginning to be explored only recently. We carried out a whole genome-based linkage analysis in a family where most of its members affected by HWE and found evidence of a previously unknown locus at chromosome 9p24.3-p23. Parametric two-point analysis suggested linkage with the greatest LOD score of 3.42 for the marker D9S286 at 9p24.1 at recombination fraction (θ) = 0, 90% penetrance value and 1% phenocopy rate. The highestmultipoint LODscore of 3.42was obtained for same marker at 9p24. The critical genetic interval of about 10 Mb of DNA was defined by the markers D9S917 and D9S168 corresponding to the centromere-distal and centromere-proximal recombination boundaries, respectively. This observation along with our previous findings of hot water genetic loci at 10q21.3-q22.3 (OMIM: 613339) and 4q24-q28 (OMIM: 613340), indicates unanticipated genetic heterogeneity for the disorder in families from a relatively small geographic region in the southern parts of India.