Further genetic analysis of the Segregation Distorter complex of Drosophila melanogaster: Electron microscopy studies and identification of sequences underlying the function of Enhancer of Segregation Distortion, E (SD)

The Segregation Distorter (SD) complex of genes on the second chromosome of Drosophila melanogaster has been the subject of research for over forty years since its isolation from natural populations. The interaction of the variant loci on an SD chromosome with a sensitive target called Responder ( Rsp) within a male germline results in the dysfunction of the Rsp bearing sperm. This dissertation has focused on cloning one of the SD variant loci called Enhancer of Segregation Distortion (E(SD)) utilizing three approaches that included positional cloning, RAPD-PCR to detect SD chromosome specific polymorphisms and P element mutagenesis. From these studies, I have derived a preliminary map of the genomic region to which E(SD) has been localized and identified polymorphic DNAs on SD chromosomes that may be useful in future mapping experiments. Additionally, a genetically modified P transposable element called SUPor-P has been inserted into the heterochromatin of an SD chromosome derivative that carries E(SD). Excision of the transposon from this chromosome can result in derivatives that are deleted for E(SD) function. This result indicates that the P element insert is sufficiently close to E( SD) to further mutagenize and aid in the cloning of the locus.;Two other studies were initiated during my dissertation that are presented here. The first study reexamines the ultrastructural phenotype of spermatogenesis in SD males, The original transmission electron microscopy surveys in heterozygous SD males over twenty years ago found a late maturation defect in half of the spermatids. This finding contradicts genetic and molecular data that indicates that the SD components act at an earlier stage of sperm maturation. To address this discrepancy, I reexamined spermatogenesis at the ultrastructural level in males in which SD-mediated drive is occurring in nearly all sperm. The second study was a collaborative effort in which a megabase physical map was derived for the pericentromeric Rsp locus. Other findings that include the identification of a fragment that may contain the second chromosome centromere are presented in that chapter.