An adaptive hypothesis for the evolution of the Y chromosome.
An adaptive hypothesis for the evolution of the Y chromosome.
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作者：
H. Orr;Y. Kim
群体遗传学家仍然不确定驱动Y染色体进化的力量。在这里，我们考虑的可能性，退化的Y反映了它无法适应性地进化。因为绝大多数非重组原Y上的有利突变都有零固定概率，所以Y的适应性一定远远落后于重组X。在某些时候，这种差异会变得如此之大，以至于选择倾向于增加（适合）X连锁等位基因的表达，减少（不适合）Y连锁等位基因的表达。我们的计算表明，这一过程的作用远比搭便车引起的Y染色体侵蚀快，至少与背景选择在Y染色体上固定有害等位基因一样快。最重要的是，这一假说可以解释Y染色体在具有非常大种群规模的分类群（如果蝇）中的进化。
Population geneticists remain unsure of the forces driving the evolution of Y chromosomes. Here we consider the possibility that the degeneration of the Y reflects its inability to evolve adaptively. Because the overwhelming majority of favorable mutations on a nonrecombining proto-Y suffer a zero probability of fixation, the fitness of the Y must lag far behind that of the recombining X. At some point, this disparity will grow so large that selection favors an increase in the expression of (fit) X-linked alleles and a decrease in the expression of (unfit) Y-linked alleles. Our calculations suggest that this process acts far more rapidly than hitchhiking-induced erosion of the Y and at least as rapidly as the fixation of deleterious alleles on the Y by background selection. Most important, this hypothesis can explain the evolution of Y chromosomes in taxa such as Drosophila that have very large population sizes.