Department of Zoology, Charles University in Prague, Vinicná 7, 128 44, Prague 2, Czech Republic.
J Mol Evol. 2010 Feb;70(2):129-36. doi: 10.1007/s00239-009-9315-5. Epub 2009 Dec 27.
Theory predicts that sexually antagonistic mutations will be over- or under-represented on the X and Z chromosomes, depending on their average dominance coefficients. However, as little is known about the dominance coefficients for new mutations, the effect of sexually antagonistic selection is difficult to predict. To elucidate the role of sexually antagonistic selection in the evolution of Z chromosome gene content in chicken, we analyzed publicly available microarray data from several somatic tissues as well as somatic and germ cells of the ovary. We found that the Z chromosome is enriched for genes showing preferential expression in ovarian somatic cells, but not for genes with preferential expression in primary oocytes or non-sex-specific somatic tissues. Our results suggest that sexual antagonism leads to a higher abundance of female-benefit alleles on the Z chromosome. No bias toward Z-linkage for oocyte-enriched genes can be explained by lower intensity of sexually antagonistic selection in ovarian germ cells compared to ovarian somatic cells. An alternative explanation would be that meiotic Z chromosome inactivation hinders accumulation of oocyte-expressed genes on the Z chromosome. Our results are consistent with findings in mammals and indicate that recessive rather than dominant sexually antagonistic mutations shape the gene content of the X and Z chromosomes.
理论预测，根据其平均显性系数，性拮抗突变在 X 和 Z 染色体上的表现程度会过高或过低。然而，由于对新突变的显性系数知之甚少，因此性拮抗选择的影响难以预测。为了阐明性拮抗选择在鸡 Z 染色体基因组成进化中的作用，我们分析了来自几种体组织以及卵巢体细胞和生殖细胞的公开可用的微阵列数据。我们发现，Z 染色体富含在卵巢体细胞中优先表达的基因，但在初级卵母细胞或非性别特异性体组织中优先表达的基因则不然。我们的结果表明，性拮抗导致 Z 染色体上雌性有利等位基因的丰度更高。对于卵母细胞富集基因没有偏向 Z 连锁的现象，可以解释为与卵巢体细胞相比，卵巢生殖细胞中的性拮抗选择强度较低。另一种解释是，减数分裂 Z 染色体失活阻碍了 Z 染色体上卵母细胞表达基因的积累。我们的结果与哺乳动物的发现一致，并表明是隐性而非显性的性拮抗突变塑造了 X 和 Z 染色体的基因组成。
