Induction of Crossing-over in Drosophila Males by Means of Ovarian Extract

THE frequency of gene recombination is known to be affected by extrinsic factors or intrinsic ones such as sex. Crossing-over is completely blocked in dipteran males, including those of Drosophila melanogaster , and in silkworm females. It is a puzzling problem why sex should have such an influence on crossing-over. Lack of homology between regions of the X and Y may explain the absence of crossing-over between the sex-chromosomes of the heterogametic sex, but the absence of crossing-over in the autosomes must have a different cause.