Evidence for Newly Induced Genetic Activity Responsible for Male Recombination Induction in DROSOPHILA MELANOGASTER.

The T-007 second chromosomal line of Drosophila melanogaster, previously shown to contain a major element, Mr, responsible for male recombination induction, also contains the genetic capability to induce male recombination activity into (nonhomologous) third chromosomes. This newly induced male recombination activity maps to the centromeric region of two third-chromosome lines that were subjected to mapping experiments. The ability of these third chromosome lines to induce male recombination accounts for previous observations concerning the ability of Mr(+) genotypes (derived from Mr/Mr(+) heterozygous females) to induce male recombination for only a few generations, when only second chromosomes were selected and backcrossed. The occurrence of this effect, and a similar effect induced in the homologue of T-007, suggests a possible explanation of how natural populations of D. melanogaster have come to contain such high frequencies of these "male recombination" second and third chromosomes, despite their numerous deleterious effects.