Abstract
Crossovers in males of D. ananassae resulted in considerable variation among strains and among families. When inbred lines were used, however, the variation for families was decreased and recombination frequencies were random with respect to families. These results indicated that male crossing-over is probably controlled by polygenic systems and the chromosomes are genetically divergent.
Genetic factors which controlled male crossing-over acted on both second and third chromosomes in the present case, although there were some differences in degrees of crossing-over between them. No effects of these factors on female crossing-over were found.
Differences in frequencies of crossovers were observed between reciprocal heterozygous males, which suggested some effect of the Y chromosome on male crossing-over.
Meiotic origin of male crossing-over was suggested by the following evidence: the complementary crossover classes were balanced, the distribution of crossovers was random with respect to families, and map distances and the recombination values in males was correlated.
