Recombination and selection in the maintenance of the adaptive value of inversions

A huge amount of data seem to confirm the adaptive value of inversions in Drosophila. The inhibition of recombination in heterokaryotypes mediated by inversions seems fundamental in maintaining their adaptive role. This study shows that recombination is highly suppressed in Drosophila subobscura because of chromosomal inversions, not only inside the inversions but also outside them. It seems that the region outside the inversion where recombination is inhibited is asymmetrical and independent of the inversion length. Despite the difficulty of crossovers taking place near inversion breakpoints, the only two recombination events detected inside inversions were located close to the breakpoint. Thus, selection could be largely responsible for the recombination reduction maintaining sets of adaptive alleles inside the inverted region. Heterokaryotype descendants were always in higher frequency than inbred or outbred homokaryotypes, regardless of the geographical origin of the chromosome, suggesting that chromosomes carrying the same arrangement, although with a different set of alleles for neutral markers, could be submitted to the same selection processes.