Sundström Hannah, Webster Matthew T, Ellegren Hans
Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, SE-752 36 Uppsala, Sweden.
Genetics. 2004 May;167(1):377-85. doi: 10.1534/genetics.167.1.377.
Understanding the population genetic factors that shape genome variability is pivotal to the design and interpretation of studies using large-scale polymorphism data. We analyzed patterns of polymorphism and divergence at Z-linked and autosomal loci in the domestic chicken (Gallus gallus) to study the influence of mutation, effective population size, selection, and demography on levels of genetic diversity. A total of 14 autosomal introns (8316 bp) and 13 Z-linked introns (6856 bp) were sequenced in 50 chicken chromosomes from 10 highly divergent breeds. Genetic variation was significantly lower at Z-linked than at autosomal loci, with one segregating site every 39 bp at autosomal loci (theta(W) = 5.8 +/- 0.8 x 10(-3)) and one every 156 bp on the Z chromosome (theta(W) = 1.4 +/- 0.4 x 10(-3)). This difference may in part be due to a low male effective population size arising from skewed reproductive success among males, evident both in the wild ancestor-the red jungle fowl-and in poultry breeding. However, this effect cannot entirely explain the observed three- to fourfold reduction in Z chromosome diversity. Selection, in particular selective sweeps, may therefore have had an impact on reducing variation on the Z chromosome, a hypothesis supported by the observation of heterogeneity in diversity levels among loci on the Z chromosome and the lower recombination rate on Z than on autosomes. Selection on sex-linked genes may be particularly important in organisms with female heterogamety since the heritability of sex-linked sexually antagonistic alleles advantageous to males is improved when fathers pass a Z chromosome to their sons.
了解塑造基因组变异性的群体遗传因素对于利用大规模多态性数据进行研究的设计和解释至关重要。我们分析了家鸡（原鸡）Z染色体连锁和常染色体位点的多态性和分化模式，以研究突变、有效种群大小、选择和种群统计学对遗传多样性水平的影响。对来自10个高度分化品种的50条鸡染色体中的14个常染色体内含子（8316 bp）和13个Z染色体连锁内含子（6856 bp）进行了测序。Z染色体连锁位点的遗传变异显著低于常染色体位点，常染色体位点每39 bp有一个分离位点（θ(W)=5.8±0.8×10^(-3)），Z染色体上每156 bp有一个分离位点（θ(W)=1.4±0.4×10^(-3)）。这种差异可能部分是由于雄性生殖成功的偏态导致雄性有效种群大小较低，这在野生祖先红原鸡和家禽育种中都很明显。然而，这种效应并不能完全解释观察到的Z染色体多样性降低三到四倍的现象。因此，选择，特别是选择性清除，可能对降低Z染色体上的变异产生了影响，这一假设得到了Z染色体上不同位点多样性水平的异质性以及Z染色体上重组率低于常染色体的观察结果的支持。在雌性异配性别的生物体中，对性连锁基因的选择可能尤为重要，因为当父亲将Z染色体传给儿子时，有利于雄性的性连锁性拮抗等位基因的遗传力会提高。
