Prior studies of recombination which monitor exchange events in exceedingly short intervals (i.e., separable sites within a cistron) reveal that the basic event in recombination involves a non-reciprocal transfer of information, termed conversion. As a logical consequence of the model suggested by the work in Drosophila, the present investigation examined recombination between rosy mutant alleles (ry:3-52.0) in Drosophila melanogaster in a paracentric inversion (In(3R)P18) heterozygote, which placed the rosy region approximately at the center of the inverted region. Comparison of the results of this study with experiments carried out in standard chromosome homozygotes reveals a dramatic suppression of classical crossovers between the rosy mutant alleles in the inversion heterozygote. However, conversions continue to occur for all rosy mutant alleles in all heterozygous combinations in the inversion heterozygote. Moreover, the order of magnitude of conversion frequencies seen in the inversion heterozygote does not change from that seen in the standard chromosome homozygote study. The significance of these observations with reference to the role of rearrangements as barriers of information transfer is discussed. Particular attention is directed to the elaborate inversion polymorphisms seen in natural populations, and to notions concerning their role in the evolution of adaptive gene complexes.
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