Institute of Science and Technology Austria, Klosterneuburg, Austria.
Genetics. 2010 Dec;186(4):1389-410. doi: 10.1534/genetics.110.123240. Epub 2010 Oct 5.
Biological traits result in part from interactions between different genetic loci. This can lead to sign epistasis, in which a beneficial adaptation involves a combination of individually deleterious or neutral mutations; in this case, a population must cross a "fitness valley" to adapt. Recombination can assist this process by combining mutations from different individuals or retard it by breaking up the adaptive combination. Here, we analyze the simplest fitness valley, in which an adaptation requires one mutation at each of two loci to provide a fitness benefit. We present a theoretical analysis of the effect of recombination on the valley-crossing process across the full spectrum of possible parameter regimes. We find that low recombination rates can speed up valley crossing relative to the asexual case, while higher recombination rates slow down valley crossing, with the transition between the two regimes occurring when the recombination rate between the loci is approximately equal to the selective advantage provided by the adaptation. In large populations, if the recombination rate is high and selection against single mutants is substantial, the time to cross the valley grows exponentially with population size, effectively meaning that the population cannot acquire the adaptation. Recombination at the optimal (low) rate can reduce the valley-crossing time by up to several orders of magnitude relative to that in an asexual population.
生物特征部分源于不同基因座之间的相互作用。这可能导致正表型相互作用，其中有益的适应涉及单独有害或中性突变的组合；在这种情况下，种群必须穿过“适应谷”才能适应。重组可以通过组合来自不同个体的突变来辅助这个过程，也可以通过打断适应性组合来减缓这个过程。在这里，我们分析了最简单的适应谷，其中一个适应需要两个基因座的每个突变提供适应优势。我们提出了一个理论分析，研究了重组对跨越所有可能参数范围的适应谷穿越过程的影响。我们发现，低重组率可以使适应谷的穿越速度相对于无性繁殖的情况更快，而较高的重组率则会减缓适应谷的穿越速度，这两种情况之间的转变发生在基因座之间的重组率大约等于适应提供的选择优势的情况下。在大种群中，如果重组率较高且对单突变体的选择很强，则穿越适应谷的时间会随着种群规模呈指数级增长，这实际上意味着种群无法获得适应。与无性繁殖种群相比，最优（低）重组率可以将穿越适应谷的时间减少几个数量级。
