Recombination and response to selection in Drosophila melanogaster.

Most biologists beleive that recombination speeds response to selection for traits determined by polygenic loci. To test this hypothesis, sixteen Drosophila melanogaster populations were selected for positive phototaxis for twenty-one generations. In some populations, balancer chromosomes were used to suppress autosomal recombination, and in others the autosomes were free to recombine. Suppression of recombination had no effect on mean rate of response to selection, though it may have increased variability in the rate of response among replicate lines. Suppressed recombination lines did not shift selection response to the freely recombining X chromosomes, despite fairly large increased in X chromosome recombination. The results suggest that in populations of moderate size, sex does not accelerate short term response to selection.