Accelerated adaptive evolution on a newly formed X chromosome.
Accelerated adaptive evolution on a newly formed X chromosome.
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DOI：
10.1371/journal.pbio.1000082
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发表时间：
2009-04-14
期刊：
影响因子：
9.8
通讯作者：
Zhang Z
中科院分区：
文献类型：
--
作者：
Bachtrog D;Jensen JD;Zhang Z
性染色体起源于普通的常染色体，它们的进化特征是从祖先Y染色体持续丢失基因。在这里，我们记录了性染色体进化的一个新特征：对新形成的X染色体的适应性固定的爆发。利用最近形成的新的X染色体的果蝇米兰达，我们比较模式的DNA序列变异基因位于新的X上的祖先X染色体上的基因。这种对比使我们能够在控制人口效应的同时，相对于基因组中的背景适应水平，推断新形成的X染色体上的选择。染色体范围内的同义多样性的新X减少2倍，相对于祖先X，预期在最近和经常性的定向选择。利用数据的各种特征进行的几项统计测试一致地确定了10%-15%的neo-X基因是最近适应性进化的目标，但只有1%-3%的基因在祖先X上。此外，无论是适应的速度和适应性取代的健身效果估计是大约一个数量级高的neo-X基因相对于祖先X的基因。因此，新形成的X染色体在性染色体分化的进化过程中并不是被动的参与者，而是适应性地对它们的性别偏向传递和Y染色体变性做出反应，可能是通过它们的基因内容的去男性化和剂量补偿的进化。在动物和植物中，性染色体已经从普通染色体独立进化了许多次。许多关于性染色体进化的研究都集中在Y染色体基因的退化和丢失上。在这里，我们描述了性染色体进化的另一个原理：对新形成的X染色体的适应性固定的爆发。通过采用比较群体基因组学方法，并利用最近形成的性染色体在果蝇米兰达，我们表明，适应率增加约10倍，在一个新形成的X染色体相对于背景水平的选择基因组。这表明，年轻的X染色体适应性地响应其女性偏向的传输和Y染色体变性。因此，与传统的被动参与者观点相反，X染色体在性染色体分化的进化过程中发挥着非常积极的作用。性染色体分子进化的研究主要集中在Y染色体的退化上，但新的证据强调，重要的变化发生在进化的X染色体上，以适应性进化的快速爆发的形式。
Sex chromosomes originated from ordinary autosomes, and their evolution is characterized by continuous gene loss from the ancestral Y chromosome. Here, we document a new feature of sex chromosome evolution: bursts of adaptive fixations on a newly formed X chromosome. Taking advantage of the recently formed neo-X chromosome of Drosophila miranda, we compare patterns of DNA sequence variation at genes located on the neo-X to genes on the ancestral X chromosome. This contrast allows us to draw inferences of selection on a newly formed X chromosome relative to background levels of adaptation in the genome while controlling for demographic effects. Chromosome-wide synonymous diversity on the neo-X is reduced 2-fold relative to the ancestral X, as expected under recent and recurrent directional selection. Several statistical tests employing various features of the data consistently identify 10%–15% of neo-X genes as targets of recent adaptive evolution but only 1%–3% of genes on the ancestral X. In addition, both the rate of adaptation and the fitness effects of adaptive substitutions are estimated to be roughly an order of magnitude higher for neo-X genes relative to genes on the ancestral X. Thus, newly formed X chromosomes are not passive players in the evolutionary process of sex chromosome differentiation, but respond adaptively to both their sex-biased transmission and to Y chromosome degeneration, possibly through demasculinization of their gene content and the evolution of dosage compensation. Sex chromosomes have evolved independently many times in both animals and plants from ordinary chromosomes. Much research on sex chromosome evolution has focused on the degeneration and loss of genes from the Y chromosome. Here, we describe another principle of sex chromosome evolution: bursts of adaptive fixations on a newly formed X chromosome. By employing a comparative population genomics approach and taking advantage of the recently formed sex chromosomes in the fruit fly Drosophila miranda, we show that rates of adaptation are increased about 10-fold on a newly formed X chromosome relative to background levels of selection in the genome. This suggests that a young X chromosome responds adaptively to both its female-biased transmission and to Y chromosome degeneration. Thus, contrary to the traditional view of being passive players, the X chromosome has a very active role in the evolutionary process of sex chromosome differentiation. Research on sex chromosome molecular evolution has focused on the degeneration of the Y chromosome, but new evidence highlights that important changes occur on the evolving X chromosome in the form of rapid bursts of adaptive evolution.
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影响因子：
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作者：
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通讯作者：
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DOI：
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发表时间：
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影响因子：
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