SYNERGISTIC INTERACTION BETWEEN PARTICULAR X-CHROMOSOME DELETIONS ANDSEX-LETHAL CAUSES FEMALE LETHALITY IN DROSOPHILA-MELANOGASTER

We studied the effect on female viability of trans-heterozygous combin ations of X-chromosome deficiencies and Sxt-(fl), a null allele of Sex -lethal. Twentyfive deficiencies, which together covered 80% of the X chromosome, were tested. Seven of these trans-heterozygous combination s caused significant levels of female lethality. Two of the seven inte racting deficiencies include the previously known sex determination ge nes sans fille and sisterless-a. Four of the remaining uncover X-chrom osomal regions that were not hitherto known to contain sex determinati on genes. These newly identified regions are defined by deficiencies D f(1)RA2 (7D10; 8A4-5), Df(1)KA14 (7F1-2; 8C6), Df(1)C52 (8E; 9C-D) and Df(1)N19 (17A1; 18A2). These four deficiencies were characterized fur ther to determine whether it was the maternal or zygotic dosage that w as primarily responsible for the observed lethality of female embryos, daughterless and extra macrochaetae, two known regulators of Sxl, inf luence the interaction of these deficiencies with Sxl.