The Chicken (Gallus gallus) Z Chromosome Contains at Least Three Nonlinear Evolutionary Strata
The Chicken (Gallus gallus) Z Chromosome Contains at Least Three Nonlinear Evolutionary Strata
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DOI：
10.1534/genetics.108.090324
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发表时间：
2008-10-01
期刊：
影响因子：
3.3
通讯作者：
Ellegren, Hans
中科院分区：
文献类型：
--
作者：
Nam, Kiwoong;Ellegren, Hans
鸟类具有雌性异配子体，具有Z和W性染色体。这些染色体是从不同于哺乳动物X和Y的常染色体前体染色体进化而来的。然而，以前的研究表明，性染色体进化的模式和过程在远亲生物中显示出许多相似之处。在这里，我们表明，逐步限制鸟类的原生性染色体之间的重组，导致鸡Z染色体的区域显示离散水平的分歧W同系物（配子体）。分析的12个基因落入三个水平的估计的分歧值，与最近的分歧（d（S）= 0.18-0.21）显示的6个基因在Z染色体上的一个区域对应的间隔1-11 Mb的组装的基因组序列。另外4个基因表现出中等分化（d（S）= 0.27-0.38），位于16-53 Mb区间。具有较高值的两个基因（在位置42和50 Mb处）位于具有中间趋异的4个基因的最远端的近端，表明反转事件。基因的分布和它们的分歧表明至少有三个进化层，Z和W之间的重组停止的估计时间为1.32 - 1.5亿年（层1），71-99（层2）和47-57（层3）百万年前。层1和层2形成后的倒位事件或其他形式的染色体内重排打乱了基因顺序，导致鸡Z染色体上目前所见的进化层的非线性排列。这些观察结果表明，重组的渐进限制是性染色体进化的一个整体特征，也发生在雌性异配子系统中。
Birds have female heterogamety with Z and W sex chromosomes. These evolved from different autosomal precursor chromosomes than the mammalian X and Y However, previous work has suggested that the pattern and process of sex chromosome evolution show many similarities across distantly related organisms. Here we show that stepwise restriction of recombination between the protosex chromosomes of birds has resulted in regions of the chicken Z chromosome showing discrete levels of divergence from W homologs (gametologs). The 12 genes analyzed fall into three levels of estimated divergence values, with the most recent divergence (d(S) = 0.18-0.21) displayed by 6 genes in a region on the Z chromosome corresponding to the interval 1-11 Mb of the assembled genome sequence. Another 4 genes show intermediate divergence (d(S) = 0.27-0.38) and are located in the interval 16-53 Mb. Two genes (at positions 42 and 50 Mb) with higher values are located proximal to the most distal of the 4 genes with intermediate divergence, suggesting an inversion event. The distribution of genes and their divergence indicate at least three evolutionary strata, with estimated times for cessation of recombination between Z and Wof 132-150 (stratum 1), 71-99 (stratum 2), and 47-57 (stratum 3) million years ago. An inversion event, or some other form of intrachromosomal rearrangement, subsequent to the formation of strata 1 and 2 has scrambled the gene order to give rise to the nonlinear arrangement of evolutionary strata currently seen on the chicken Z chromosome. These observations suggest that the progressive restriction of recombination is an integral feature of sex chromosome evolution and occurs also in systems of female heterogamety.