Biology Department, Duke University, Durham, North Carolina.
Mol Ecol. 2019 Mar;28(6):1302-1315. doi: 10.1111/mec.14921. Epub 2018 Dec 10.
Chromosomal inversions shape recombination landscapes, and species differing by inversions may exhibit reduced gene flow in these regions of the genome. Though single crossovers within inversions are not usually recovered from inversion heterozygotes, the recombination barrier imposed by inversions is nuanced by noncrossover gene conversion. Here, we provide a genomewide empirical analysis of gene conversion rates both within species and in species hybrids. We estimate that gene conversion occurs at a rate of 1 × 10 to 2.5 × 10 converted sites per bp per generation in experimental crosses within Drosophila pseudoobscura and between D. pseudoobscura and its naturally hybridizing sister species D. persimilis. This analysis is the first direct empirical assessment of gene conversion rates within inversions of a species hybrid. Our data show that gene conversion rates in interspecies hybrids are at least as high as within-species estimates of gene conversion rates, and gene conversion occurs regularly within and around inverted regions of species hybrids, even near inversion breakpoints. We also found that several gene conversion events appeared to be mitotic rather than meiotic in origin. Finally, we observed that gene conversion rates are higher in regions of lower local sequence divergence, yet our observed gene conversion rates in more divergent inverted regions were at least as high as in less divergent collinear regions. Given our observed high rates of gene conversion despite the sequence differentiation between species, especially in inverted regions, gene conversion has the potential to reduce the efficacy of inversions as barriers to recombination over evolutionary time.
染色体倒位塑造了重组景观，而在这些基因组区域发生倒位的物种可能表现出基因流减少。尽管在倒位杂合体中通常无法恢复倒位内的单交叉，但非交叉基因转换使倒位造成的重组障碍变得复杂。在这里，我们提供了一个关于种内和种间杂种基因转换率的全基因组经验分析。我们估计，在实验交叉中，在果蝇拟暗褐果蝇内和在其与自然杂交的姐妹种黑腹果蝇之间，基因转换以每代每 bp 1×10 到 2.5×10 个转换位点的速率发生。这项分析是对种间杂种中倒位内基因转换率的首次直接经验评估。我们的数据表明，种间杂种中的基因转换率至少与种内基因转换率估计值一样高，并且基因转换经常发生在种间杂种的倒位区内和周围，即使在倒位断点附近也是如此。我们还发现，几个基因转换事件似乎起源于有丝分裂而不是减数分裂。最后，我们观察到基因转换率在局部序列差异较低的区域更高，但在差异更大的倒位区域观察到的基因转换率至少与差异较小的直向区域一样高。鉴于我们观察到的基因转换率很高，尽管物种之间存在序列分化，尤其是在倒位区域，基因转换有可能降低倒位作为重组障碍的有效性，随着进化时间的推移。
