Organisms have evolved various mechanisms to cope with the differences in the gene copy numbers between sexes caused by degeneration of Y and W sex chromosomes. Complete dosage compensation or at least expression balance between sexes has been reported predominantly in XX/XY systems, but rarely in ZZ/ZW systems. However, this often‐reported pattern is based on comparisons of lineages where sex chromosomes evolved from nonhomologous genomic regions, potentially differing in sensitivity to differences in gene copy numbers. Here we document that two reptilian lineages (XX/XY iguanas and ZZ/ZW softshell turtles), which independently co‐opted the same ancestral genomic region for the function of sex chromosomes, evolved different gene dose regulatory mechanisms. The independent co‐option of the same genomic region for the role of sex chromosomes as in the iguanas and the softshell turtles offers great opportunity for testing evolutionary scenarios on sex chromosome evolution under the explicit control of the genomic background and gene identity. We show that the parallel loss of functional genes from the Y chromosome of the green anole and the W chromosome of the Florida softshell turtle led to different dosage compensation mechanisms. Our approach controlling for genetic background thus does not support that the variability in the regulation of gene dose differences is a consequence of ancestral autosomal gene content.

中文翻译：

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剂量补偿的演变不取决于基因组背景

生物体已经进化出各种机制来应对由Y和W性染色体变性引起的性别之间的基因拷贝数差异。在XX / XY系统中主要报道了完全的剂量补偿或至少性别之间的表达平衡，但在ZZ / ZW系统中很少报道。但是，这种经常报告的模式是基于对性染色体从非同源基因组区域进化而来的谱系的比较，这些谱系对基因拷贝数差异的敏感性可能存在差异。在这里，我们记录了两个爬行动物谱系（XX / XY鬣蜥和ZZ / ZW soft），为性染色体的功能独立选择了相同的祖先基因组区域，它们进化出了不同的基因剂量调节机制。与在鬣蜥和the中相同的基因组区域对性染色体的作用的独立选择，为在基因组背景和基因特性的明确控制下测试性染色体进化的进化场景提供了巨大的机会。我们表明，功能基因的平行损失从绿色的Anole的Y染色体和佛罗里达的turtle的W染色体导致了不同的剂量补偿机制。因此，我们控制遗传背景的方法不支持基因剂量差异调节中的变异性是祖先常染色体基因含量的结果。