Filatov D A
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, UK.
Genet Res (Camb). 2008 Feb;90(1):85-95. doi: 10.1017/S0016672307009056.
The most prominent feature of Y chromosomes is that they do not recombine and are usually genetically degenerate, containing only a few genes. White campion Silene latifolia has evolved sex chromosomes relatively recently, probably within the last 10-15 million years. Perhaps due to its recent origin, the Y chromosome in this species has not completely degenerated and most isolated X-linked genes have intact Y-linked homologues. A gene encoding a protein with strong homology to spermidine synthases, Slss, is the exception to this rule, as the Y-linked copy of this gene has apparently lost its function. Here I report evidence for a recent selective sweep in the X-linked copy of this gene (SlssX) that could reflect compensatory evolution in an X-linked gene that has lost a functional Y-linked homologue. The spread and fixation of an advantageous mutation in SlssX has resulted in a dramatic loss of genetic diversity and an excess of high-frequency derived polymorphisms in this gene. As the sweep has not affected the closely linked DD44X gene, the selective advantage of the mutation that has driven the sweep in the SlssX gene might have been less than 1%.
Y染色体最显著的特征是它们不会发生重组，通常在基因上会发生退化，只包含少数基因。白剪秋萝（Silene latifolia）相对较新地进化出了性染色体，可能是在过去的1000万到1500万年之间。也许由于其起源较近，该物种的Y染色体尚未完全退化，大多数分离的X连锁基因都有完整的Y连锁同源物。一个编码与亚精胺合成酶具有高度同源性的蛋白质的基因Slss是个例外，因为该基因的Y连锁拷贝显然已经失去了功能。在此，我报告了该基因（SlssX）的X连锁拷贝中近期发生选择性清除的证据，这可能反映了一个失去功能性Y连锁同源物的X连锁基因的补偿性进化。SlssX中一个有利突变的传播和固定导致了该基因遗传多样性的显著丧失和高频衍生多态性的过量。由于这次清除并未影响紧密连锁的DD44X基因，驱动SlssX基因清除的突变的选择优势可能小于1%。
