PDF(Pubmed)
Abstract：
Natural selection is less efficient in the absence of recombination. As a result, nonrecombining sequences, such as sex chromosomes, tend to degenerate over time. Although the outcomes of recombination arrest are typically observed after many millions of generations, recent neo-sex chromosomes can give insight into the early stages of this process. Here, we investigate the evolution of neo-sex chromosomes in the Spanish marbled white butterfly, Melanargia ines, where a Z-autosome fusion has turned the homologous autosome into a nonrecombining neo-W chromosome. We show that these neo-sex chromosomes are likely limited to the Iberian population of M. ines, and that they arose around the time when this population split from North-African populations, around 1.5 million years ago. Recombination arrest of the neo-W chromosome has led to an excess of premature stop-codons and frame-shift mutations, and reduced gene expression compared to the neo-Z chromosome. Surprisingly, we identified two regions of ∼1 Mb at one end of the neo-W that are both less diverged from the neo-Z and less degraded than the rest of the chromosome, suggesting a history of rare but repeated genetic exchange between the two neo-sex chromosomes. These plateaus of neo-sex chromosome divergence suggest that neo-W degradation can be locally reversed by rare recombination between neo-W and neo-Z chromosomes.
摘要：
在没有重组的情况下自然选择效率较低。因此,非重组序列，比如性染色体，随着时间的推移倾向于退化。尽管重组停滞的结果通常是在数百万代之后观察到的，最近的新性染色体可以深入了解这一过程的早期阶段。在这里，我们研究了西班牙大理石白黄油中新性染色体的表达，黑色素瘤，其中Z-常染色体融合已将同源常染色体变成非重组neo-W染色体。我们表明这些新性染色体可能仅限于伊比利亚的M.ines种群，它们出现在这个人口与北非人口分裂的时候，大约150万年前。新W染色体的重组停滞导致了过多的过早终止密码子和移码突变,与neo-Z染色体相比，基因表达减少。令人惊讶的是,weidentifiedtworegionsof~1Mbatoneendoftheneo-Wthatarebothlessdivergedfromtheneo-Zandlessdegradedthantherestofthe染色体,这表明两条新性染色体之间有罕见但重复的遗传交换史。这些新性染色体差异的平台表明，neo-W和neo-Z染色体之间的罕见重组可以局部逆转neo-W降解。
