A genetic and molecular analysis of the Triplo-lethal locus of Drosophila melanogaster

Douglas R Dorer, Thomas Jefferson University


Most cases of lethality associated with aneuploidy in Drosophila melanogaster are caused by the cumulative effects of the incorrect dosage of a large number of genes. A unique exception to this is the Triplo-lethal locus, Tpl. Individual flies bearing either one or three copies of Tpl usually die as late embryos with no obvious morphological abnormalities. Little is known about the biology of Tpl, though mutational analysis of the locus has indicated that it consists of functionally redundant genetic information or is in some other way resistant to point mutations. This thesis includes a description of a recombinational hotspot associated with hypomorphic alleles of Tpl. Transposon insertions are proposed to be responsible for both the Tpl mutations and the site-specific increase in recombination frequency. Mutants recovered from a P x M dysgenic cross and from the mobilization of single P element inserts near Tpl are described. In addition to cytologically visible duplications and deficiencies, the dysgenic crosses produce cytologically normal hypomorphic alleles. Also, it had been previously observed that duplications for a region of the X chromosome could suppress the triplo-lethal phenotype of Tpl. The cytogenetic characterization of the locus known as Isis which is responsible for this phenomenon is reported here. The molecular cloning of portions of the 83E chromosomal region which contains Tpl is described. An entry point into the region was provided by a P element insertion in a hypomorphic mutant chromosome. This insertion was found to be located within the gene for a putative RNA helicase, RM62. Two Tpl duplication breakpoints were mapped which have ruled out RM62 by itself as being responsible for Tpl. Cloning the 83E region has made it possible to correlate molecular polymorphisms with events associated with the recombinational hotspot.

Subject Area

Genetics|Molecular biology

Recommended Citation

Dorer, Douglas R, "A genetic and molecular analysis of the Triplo-lethal locus of Drosophila melanogaster" (1992). ETD Collection for Thomas Jefferson University. AAI9227563.