Differential sensitivities and the target of heat-induced recombination at the base of the X chromosome of Drosophila melanogaster.

The effect of heat on two small adjacent segments at the base of the X chromosome was examined. Recombination in the two segments delimited by recessive lethals was measured after treatment with 30 degree and 34 degree. Both segments were sensitive at 30 degree, while only the proximal one responded to 34 degree treatment. When the same segments were studied in structural heterozygotes (for deletions) the relative increase in recombination was greater, suggesting that heat exerts its effect on the "pairing" rather than the "exchange" components of crossing over. The effect of c (3) G/+ on the same segments in both homozygous and heterozygous structurals was studied. The results indicate that this meiotic mutant mediates its effect on a step different than that affected by heat.