Chicken W: A genetically uniform chromosome in a highly variable genome
Chicken W: A genetically uniform chromosome in a highly variable genome
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DOI：
10.1073/pnas.0405126101
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发表时间：
2004-11-09
影响因子：
11.1
通讯作者：
Ellegren, H
中科院分区：
文献类型：
--
作者：
Berlin, S;Ellegren, H
由于有效种群大小是常染色体的四分之一，因此具有雄性异配子的生物体的Y染色体预计会显示出较低的遗传多样性水平。然而，对哺乳动物、苍蝇和植物的研究表明，即使考虑到有效种群大小的差异，Y染色体多样性也低于预期。这可能是由于雄性繁殖成功率的不平衡，导致雄性有效种群规模较小，或者是由于选择在塑造非重组染色体的核苷酸多样性水平方面发挥了强大的作用。通过对10个高度分化品种的47只鸡的7643对碱基对进行重测序，估计了家鸡雌性特异性W染色体的核苷酸多样性，我们在雌性异配子系统中验证了这些假设。筛选只显示了一个单独的分离位点，这与我们之前的观察结果形成鲜明对比，我们使用类似的鸟类小组，在常染色体序列中平均每39个碱基对有一个分离位点。当考虑到性别特异性突变率和有效群体大小的差异时，观察到的W染色体多态性程度比分离位点频率的预期低28倍，比核苷酸多样性估计的预期低13倍(常染色体，6.5 x 10(-3)；W, 7.0 x 10(-5))。我们注意到，选择是唯一可以解释性别限制染色体多样性减少的因素，而不管生殖方式如何，也不管是否存在雄性或雌性异型配子。女性特异性W染色体变异性的降低不容易用性选择来解释。
The Y chromosome of organisms with male heterogamety is expected to show reduced levels of genetic diversity, because the effective population size is one-fourth that of autosomes. However, studies in mammals, flies, and plants show that Y chromosome diversity is lower than expected even when differences in effective population size are taken into account. This may be explained by skewed reproductive success among males, leading to low male effective population size, or by a strong role of selection in shaping levels of nucleotide diversity in nonrecombining chromosomes. We tested these hypotheses in a system with female heterogamety by estimating nucleotide diversity in the female-specific W chromosome of the domestic chicken by resequencing of 7,643 base pairs in 47 birds from 10 highly divergent breeds. The screening revealed only one single segregating site, which is in sharp contrast to our previous observation, using a similar panel of birds of, on average, one segregating site every 39 base pairs in autosomal sequence. When taking sex-specific mutation rates and differences in effective population size into account, the observed degree of W chromosome polymorphism is 28-fold lower than expected for the frequency of segregating sites and 13-fold lower than expected for estimates of nucleotide diversity (autosomes, 6.5 x 10(-3); W, 7.0 x 10(-5)). We note that selection is the only factor that can explain the reduced diversity in the sex-limited chromosome irrespective of mode of reproduction or whether there is male or female heterogamety. Reduced variability in female-specific W chromosomes is not easily explained by sexual selection.