Evolutionary rates in mitochondrial vs. non-mitochondrial proteins. (A) A schematic phylogeny of a mt-cy two gene family with gene duplication occurred in the vertebrate lineage. Branch lengths before the divergence between fish and tetrapods are marked as a and b for mitochondrial and cytosolic proteins, respectively. The corresponding average branch lengths after this divergence are marked as a' and b'. (B) The ratios of branch lengths for mitochondrial vs. nuclear paralogs (a/b, a'/b', and (a+a')/(b+b')) were calculated on the maximum likelihood topologies as illustrated in (A) with the exception of the TST family, for which the divergence between birds (chicken) and mammals was used. TOP1MT, TST, SHMT2 and CDS2 families had undergone relocalization from cytosol to mitochondria, while the remaining 6 families had the opposite direction of relocalizations.