Selection for reduced crossing over in Drosophila melanogaster.

Selection was practiced for reducing crossing over between the third chromosome genes Sb and H(2) of Drosophila melanogaster; the method employed was to select the repulsion double heterozygotes Sb+/+H(2) every generation. Two replicate selection lines were maintained. After 24 generations of selection, Line 1 showed no significant difference from the control, although the regression of recombination value on generation was significant. In generation 20, Line 2 had a significantly lower recombination value than the control, as well as having a highly significant regression coefficient. No chromosome rearrangements were involved in the response. It was concluded that there was substantial genic variability in the frequency of crossing over between Sb and H(2) in the base population.