The nature of genetic recombination near the third chromosome centromere or Drosophila melanogaster.

Previous studies have indicated that recombination near the third chromosome centromere is associated with negative chromosome interference, a phenomenon for which Green (1975) and Sinclair (1975) suggested gene conversion as a possible mechanism. In this report, we demonstrate that negative chromosome interference is still observed when deficiencies or translocation breakpoints are scored as the middle markers in recombination experiments and the rate of recombination is increased by interchromosomal effect. We argue that these chromosomal rearrangement breakpoints are not subject to conversion. Since neither successive premeiotic and meiotic exchanges, nor negative chromatid interference, can by themselves account for the negative chromosome interference, we conclude that a greater than expected frequency of multiple exchanges actually occurs. We further suggest that negative chromosome interference may be characteristic of all chromosomal regions normally showing very little exchange in relation to physical length.