Section of Integrative Biology, The University of Texas at Austin, Austin, TX, USA.
Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
J Evol Biol. 2012 Oct;25(10):1947-1954. doi: 10.1111/j.1420-9101.2012.02591.x. Epub 2012 Aug 17.
Sex chromosomes are expected to evolve suppressed recombination, which leads to degeneration of the Y and heteromorphism between the X and Y. Some sex chromosomes remain homomorphic, however, and the factors that prevent degeneration of the Y in these cases are not well understood. The homomorphic sex chromosomes of the European tree frogs (Hyla spp.) present an interesting paradox. Recombination in males has never been observed in crossing experiments, but molecular data are suggestive of occasional recombination between the X and Y. The hypothesis that these sex chromosomes recombine has not been tested statistically, however, nor has the X-Y recombination rate been estimated. Here, we use approximate Bayesian computation coupled with coalescent simulations of sex chromosomes to quantify X-Y recombination rate from existent data. We find that microsatellite data from H. arborea, H. intermedia and H. molleri support a recombination rate between X and Y that is significantly different from zero. We estimate that rate to be approximately 10(5) times smaller than that between X chromosomes. Our findings support the notion that very low recombination rate may be sufficient to maintain homomorphism in sex chromosomes.
性染色体通常会进化为抑制重组，导致 Y 染色体退化和 X 染色体与 Y 染色体的异态性。然而，有些性染色体仍然是同态的，目前还不清楚是什么因素阻止了这些情况下 Y 染色体的退化。欧洲树蛙（Hyla spp.）的同态性染色体呈现出一个有趣的悖论。在交叉实验中从未观察到雄性的重组，但分子数据表明 X 染色体和 Y 染色体之间偶尔会发生重组。然而，目前还没有对这些性染色体发生重组的假设进行统计检验，也没有估计 X-Y 重组率。在这里，我们使用近似贝叶斯计算和性染色体的合并模拟来从现有数据中定量 X-Y 重组率。我们发现，来自 H. arborea、H. intermedia 和 H. molleri 的微卫星数据支持 X 染色体和 Y 染色体之间的重组率与零显著不同。我们估计该速率比 X 染色体之间的重组率小约 10^5 倍。我们的研究结果支持这样一种观点，即非常低的重组率可能足以维持性染色体的同态性。
