Compared to other enhancers, heart enhancers are not subject to more frequent GC-biased gene conversions. Heart enhancers (A) are not preferentially localized to genomic regions with higher recombination rates and (B) do not contain more A/T to G/C substitutions in the mouse lineages. The values of upper quartile, median, and lower quartile are indicated in each box, whereas the bars outside the box indicate semi-quartile ranges. Pairwise comparisons showing significant differences are connected with gray lines (*0.01<P≦0.05 and ***P≦0.001 by Mann-Whitney U test). FB, forebrain; MB, midbrain; LB, limb; HT, heart.