Abstract

Genetic and physical mapping of the guppy (Poecilia reticulata) have shown that recombination patterns differ greatly between males and females. Crossover events occur evenly across the chromosomes in females, but in male meiosis they are restricted to the tip furthest from the centromere of each chromosome, creating very high recombination rates per megabase, as in pseudoautosomal regions of mammalian sex chromosomes. We used GC content to indirectly infer recombination patterns on guppy chromosomes, based on evidence that recombination is associated with GC-biased gene conversion, so that genome regions with high recombination rates should be detectable by high GC content. We used intron sequences and third positions of codons to make comparisons between sequences that are matched, as far as possible, and are all probably under weak selection. Almost all guppy chromosomes, including the sex chromosome (LG12), have very high GC values near their assembly ends, suggesting high recombination rates due to strong crossover localization in male meiosis. Our test does not suggest that the guppy XY pair has stronger crossover localization than the autosomes, or than the homologous chromosome in the close relative, the platyfish (Xiphophorus maculatus). We therefore conclude that the guppy XY pair has not recently undergone an evolutionary change to a different recombination pattern, or reduced its crossover rate, but that the guppy evolved Y-linkage due to acquiring a male-determining factor that also conferred the male crossover pattern. We also identify the centromere ends of guppy chromosomes, which were not determined in the genome assembly.

中文翻译：

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使用GC含量比较孔雀鱼（Poecilia reticulata）及其近亲物种的性染色体和常染色体上的重组模式。

摘要

孔雀鱼（Poecilia reticulata）的遗传和物理图谱）表明，男性和女性之间的重组模式差异很大。交换事件在雌性染色体上均匀地发生，但是在雄性减数分裂中，它们被限制在离每个染色体着丝点最远的末端，从而每兆碱基产生很高的重组率，例如在哺乳动物性染色体的拟常染色体区域中。基于重组与GC偏向基因转化相关的证据，我们使用GC含量间接推断孔雀鱼染色体上的重组模式，因此高GC含量应可检测到具有高重组率的基因组区域。我们使用内含子序列和密码子的第三个位置在尽可能匹配且可能都处于弱选择下的序列之间进行比较。几乎所有的孔雀鱼染色体 包括性染色体（LG12）在内的装配末端附近都有很高的GC值，这表明由于雄性减数分裂中强烈的交叉定位，重组率很高。我们的测试未表明，孔雀鱼XY对的交叉定位比常染色体或近亲鸭嘴兽的同源染色体要强（Xiphophorus maculatus）。因此，我们得出的结论是，孔雀鱼XY对最近没有经历过进化转变为不同的重组模式，或降低了其交叉速率，但是由于获得了雄性决定因素（同时赋予了雄性交叉模式），而孔雀鱼进化了Y链。 。我们还确定了孔雀鱼染色体的着丝粒末端，这在基因组装配中没有确定。