The location of a mutator factor in a strain of Drosophila melanogaster by assaying male recombination.

In a set of "mutation accumulation lines," of Drosophila melanogaster that had originated from two different wild-caught lethal-carrying second chromosomes (Yamaguchi and Mukai 1974; Mukai and Cockerham 1977; Voelker, Schaffer and Mukai 1980) a correlation exists between high rates of reverse mutation at two visible loci and the ability to induce male recombination (Scobie and Schaffer 1982). The second and third chromosomes were extracted from the lines demonstrating these phenomena and tested for independent ability to induce male recombination. When the wild chromosome being tested was of male origin extracted second chromosome lines were found to induce moderate to high levels of male recombination and reduced transmission frequency of the wild chromosome (the k value). The recombinants recovered in these crosses also demonstrated a high level of double-crossover recombination without the recovery of the reciprocal double-recombinant types. In addition, identifiable portions of extracted second chromosomes of male origin have been placed on very similar, marked genetic backgrounds and tested for their ability to induce male recombination. Results of this procedure have identified two regions of the second chromosome that induce male recombination and reduce k values. These results are consistent with the hypothesis that there exist two mutator factors and the second chromosome, each associated with a "mutation accumulation line" with an unstable locus.