EFFECTS OF AUTOSOMAL INVERSIONS ON MEIOTIC EXCHANGE IN DISTAL AND PROXIMAL REGIONS OF THE X-CHROMOSOME IN A NATURAL-POPULATION OF DROSOPHILA-MELANOGASTER

We have investigated the interchromosomal effect of the naturally-occu rring paracentric inversions In(2L)t and In(3R)P on meiotic recombinat ion in two regions of the X chromosome in Drosophila melanogaster. Pre vious authors have suggested that the rate of recombination at the tip of the X chromosome may be substantially higher in some natural popul ations than values measured in the laboratory, due to the interchromos omal effect of heterozygous autosomal inversions. This suggestion was motivated by observations that transposable elements are not as common at the tip of the X chromosome as predicted by recent research relati ng reduced meiotic exchange to increased element abundance in D. melan ogaster. We examined the effects of heterozygous In(2L)t and bz(3R)P o n recombination at both the tip and base of the X chromosome on a back ground of isogenic major chromosomes from a natural population. Both i nversions substantially increased the rate of recombination at the bas e; neither one affected recombination at the tip. The results suggest that the presence of inversions in the study population does not eleva te rates of crossing over at the tip of the X chromosome. The relevanc e of these results to ideas relating transposable element abundance to recombination rates is discussed.