Data from: Gene expression, chromosome heterogeneity and the fast-X effect in mammals

The higher rate of non-synonymous over synonymous substitutions (dN/dS) of the X chromosome compared with autosomes is often interpreted as a consequence of X hemizygosity. However, other factors, such as gene expression, are also known to vary between X and autosomes. Analysing 4800 orthologues in six mammals, we found that gene expression levels, associated with GC content, fully account for the variation in dN/dS between X and autosomes with no detectable effect of hemizygosity. We also report an extensive variance in dN/dS and gene expression between autosomes.

相较于常染色体（autosomes），X染色体（X chromosome）的错义替代与同义替代率之比（dN/dS）更高，该现象既往多被归因于X染色体的半合子状态（hemizygosity）。不过，已知X染色体与常染色体之间还存在其他差异因素，例如基因表达水平。本研究通过分析6种哺乳动物的4800个直系同源基因（orthologues），发现与GC含量（GC content）相关的基因表达水平，完全解释了X染色体与常染色体之间dN/dS的差异，且未检测到半合子状态的可观测影响。此外，本研究还发现常染色体之间的dN/dS与基因表达水平存在广泛差异。