Figure 29: Estimated average number of substitutions per site in ancestral repeat sites (tAR) (red) and in fourfold degenerate (4D) sites (t4D) (blue) for each human chromosome.
From: Initial sequencing and comparative analysis of the mouse genome
a, Estimates are made from the REV model using all aligned sites of the given type in the chromosome. Dashed lines show the genome-wide averages. Human chromosome 19 is a conspicuous outlier for its very large number of substitutions in fourfold degenerate sites (also noted in ref. 259); notably, its substitution rate in ancestral repeat sites is normal. Chromosome X shows lower rates of substitution in both types of sites, consistent with the observation that the male mutation rate is approximately twice the female rate1 (see text). Variability in neutral rates among autosomes is significant, as noted in ref. 13. b, Scatter plot of tAR against t4D for 2,424 5-Mb windows in the human genome with at least 800 aligning sites. The red line is the linear regression line (r2 = 0.22; P < 10-6).
