Premeiotic male recombination in Drosophila melanogaster.

The analysis of the cosegregation of recombinant and sex chromosomes in D. melanogaster by Hiraizumi to determine time of origin of the male recombination event(s) has been extended to include a heterologous autosome. Recombination in F1 males was measured simultaneously in marked second and third chromosomes. The results of crosses of unrelated strains in two laboratories revealed a significant excess of pairs of like-recombinant flies in the same brood that also were of the same sex and of identical genotype for the marked heterologous autosome. This nonrandom association of three chromosome pairs following meiosis, coupled with a numerical analysis that yielded estimates of the average numbers of primary spermatocytes containing either meiotic or premeiotic exchanges, provides further evidence that a large proportion of male recombination can be explained by premeiotic exchange events. Because of the additional finding of small clusters of recombinants in the same brood, it is suggested that male recombination is due to exchange in spermatogonia one or two cell divisions prior to initiation of meiosis.