EVOLUTIONARY, GENETIC, AND MOLECULAR ANALYSIS OF TRANSPOSABLE ELEMENT-INDUCED MUTATIONS IN DROSOPHILA MELANOGASTER (SELECTION, GEOTAXIS, ESTERASE-6, HYBRIDIZATION)

An analysis of transposable element-induced mutations in Drosophila melanogaster was performed to help assess the evolutionary importance of transposable element activity. The ability of transposable elements to increase the rate of response to selection was examined. Genetically similar selection lines that differed in the rate of transposition of members of the P family of transposable elements were generated from the progeny of reciprocal crosses between P and M strains, the mutually interacting strains in the P-M system of hybrid dysgenesis. These lines were subject to 14 generations of selection for changes in geotactic behavior. The responses to selection of the dysgenic lines was compared to the response to the nondysgenic lines. The results of the experiments failed to support the hypothesis that hybrid dysgenesis can increase the rate of response to selection. A second series of experiments investigated the cause of an unstable null allele of the Esterase-6 locus in Drosophila melanogaster. These experiments involved a screen for P element insertions into genes tightly linked to Esterase-6. Five complementation groups were identified in this screen. Three alleles of the rotated abdomen locus, and one allele at each of four lethal complementation groups were obtained. A molecular clone of the Esterase-6 gene was identified by in situ hybridization of DNA prepared from clones isolated in a screen of a series of genomic and cDNA clone libraries. The libraries had been screened with oligonucleotide probes that were constructed to encode a portion of the amino acid sequence of the Esterase-6 protein. An unstable null allele of Esterase-6 was found to result from insertion of a B104 transposable element into the 3' transcribed region of the Esterase-6 gene.