果蝇胚胎中X染色体上基因表达差异的过度：对快速X假说的暗示
An excess of gene expression divergence on the X chromosome in Drosophila embryos; implications for the faster-X hypothesis
摘要：
X染色体在异配子性别中以单拷贝形式存在，这种半合子性有望推动X染色体相对于常染色体的不寻常进化模式。例如，与常染色体相比，X染色体的半合子性可能导致较低的染色体有效种群大小，这表明X染色体可能更强烈地受到遗传漂变的影响。然而，X染色体也可能经历比常染色体更强的正选择，因为隐性有益突变在X染色体上的选择更明显，在那里它们将花费更少的时间被显性的、不那么有益的等位基因掩盖--这一提议被称为更快X假说。因此，实证研究表明，X染色体上的遗传趋异增加可能表明适应性或非适应性进化。我们测量了果蝇和果蝇中的基因表达。胚胎和成虫的近交系。在胚胎中，我们发现X染色体上的基因相对于常染色体上的基因的表达差异平均高出20%以上，但相比之下，在近交系中，X染色体上的基因表达变异显著较低。此外，Muller's D元件上的基因的表达趋异沿着通向暗子组的分支显著更大，在暗子组中该元件分离为新X染色体。在成人中，分歧是最大的X染色体上的男性，但不是女性，但在两种性别的近交系港口最低水平的基因表达变异的X染色体。我们认为不同的解释，我们的结果，并得出结论，他们是最一致的框架内的更快的X假设。
英文摘要：
The X chromosome is present as a single copy in the heterogametic sex, and this hemizygosity is expected to drive unusual patterns of evolution on the X relative to the autosomes. For example, the hemizgosity of the X may lead to a lower chromosomal effective population size compared to the autosomes suggesting that the X might be more strongly affected by genetic drift. However, the X may also experience stronger positive selection than the autosomes because recessive beneficial mutations will be more visible to selection on the X where they will spend less time being masked by the dominant, less beneficial allele - a proposal known as the faster-X hypothesis. Thus, empirical studies demonstrating increased genetic divergence on the X chromosome could be indicative of either adaptive or non-adaptive evolution. We measured gene expression in Drosophila species and in D. melanogaster inbred strains for both embryos and adults. In the embryos we found that expression divergence is on average more than 20% higher for genes on the X chromosome relative to the autosomes, but in contrast, in the inbred strains gene expression variation is significantly lower on the X chromosome. Furthermore, expression divergence of genes on Muller's D element is significantly greater along the branch leading to the obscura sub-group, in which this element segregates as a neo-X chromosome. In the adults, divergence is greatest on the X chromosome for males, but not for females, yet in both sexes inbred strains harbour the lowest level of gene expression variation on the X chromosome. We consider different explanations for our results and conclude that they are most consistent within the framework of the faster-X hypothesis.
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