Résumé
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.