Genetic exchange in 2La inversion heterokaryotypes of Anopheles gambiae

Abstract

In the malaria vector Anopheles gambiae, alternative arrangements of chromosome 2 (2La and 2L+(a)) vary in relative frequency along clines of aridity, suggesting the action of natural selection on targets within the inversion. Our long term goal of detecting such targets depends in part on the level of genetic exchange between arrangements. Accordingly, we estimated recombination rates on 2L from the backcross progeny of 2La/+(a) heterokaryotypes and as a control, from 2L+(a) homokaryotypes. In homokaryotypes, the recombination rate was uniform at ~2.0 centimorgans per megabase (cM/Mb). In heterokaryotypes, recombination within the rearranged region was reduced to < 0.5 cM/Mb, with slightly higher but nevertheless reduced levels (< 1.0 cM/Mb) flanking the rearrangement. Yet, gene exchange was recorded between nearly all markers, including those very near the distal inversion breakpoint. These results suggest that reduced recombination is a necessary but not sufficient mechanism for genetic isolation between alternative arrangements, and that the targets of natural selection can be identified against the different chromosomal backgrounds.

Genomic Analyses of Three Malaria Vectors Reveals Extensive Shared Polymorphism but Contrasting Population Histories

“…4 A ). Although clearly distinct, the two inversion homokaryotypes share 36 polymorphisms, indicating some level of gene flow between them (presumably due to gene conversion and double crossing-over [Stump et al 2007]). The frequency of the two chromosomal orientations did not differ between Muheza and Kilifi (χ 2 probability = 0.24) and showed no obvious deviation from Hardy–Weinberg proportions (χ 2 probability = 1.0).…”

The Population Genomics of Trans-Specific Inversion Polymorphisms in Anopheles gambiae

“…Such linkage is unlikely to have persisted as a remnant of complete inversionwide linkage disequilibrium established when the rearrangement first arose. On the basis of rates of recombination estimated in the 2La rearrangement (Stump et al 2007), the recombination fraction between e2-230k and the 2Ru distal breakpoint is expected to be roughly r ¼ 0.007. Given complete linkage disequilibrium upon origin of the inversion, in which fixed differences have linkage disequilibrium values of D 0 ¼ 0.25, D t should decay in the absence of selection to 0.001 in ,800 generations (Lewontin and Kojima 1960).…”

Gene flow and gene flux shape evolutionary patterns of variation in Drosophila subobscura

“…Nevertheless, double recombinants have been observed close to the breakpoints when analyzing the offspring of heterokaryotypic females, indicating that recombination close to the breakpoint can occur, although in very low frequency (Pegueroles et al, 2010a). As recombination between heterokaryotypes is reduced inside inverted regions (Navarro et al, 1997;Stump et al, 2007, Pegueroles et al, 2010a, higher diversity levels are expected outside inverted regions than inside them. In the region where genes can freely recombine between both arrangements (SII region, Figure 1), estimates of p sil ranged from 0.004 to 0.024 for the O ST arrangement and from 0.006 to 0.023 for O 3+4 , after excluding Yrt, as it could act as an outlier for the nucleotide variability (see Results section).…”