Figure 6

Rates of synonymous and nonsynonymous codon substitutions in exon ends over different lengths of the flanked intron. Codons split between exons were excluded from the analysis. The frequencies of both synonymous and nonsynonymous codon substitutions in exon ends flanking long introns (>1 kb, the median average mouse/rat intron length) show weak negative correlation (synonymous: R = -0.0546, P = 3.06E-27, nonsynonymous: R = -0.0297, P = 4.24E-9) with intron length. The data is for mouse/rat orthologous intron pairs. Mean standard error bars are given for each substitution rate.