Chromosomal rearrangements are associated with higher rates of molecular evolution in mammals

Evolutionary rates are not uniformly distributed across the genome. Knowledge about the biological causes of this observation is still incomplete, but its exploration has provided valuable insight into the genomical, historical and demographical variables that influence rates of genetic divergence. Recent studies suggest a possible association between chromosomal rearrangements and regions of greater divergence, but evidence is limited and contradictory. Here, we test the hypothesis of a relationship between chromosomal rearrangements and higher rates of molecular evolution by studying the genomic distribution of divergence between 12 000 human-mouse orthologous genes. Our results clearly show that genes located in genomic regions that have been highly rearranged between the two species present higher rates of synonymous (0.7686 vs. 0.7076) and non-synonymous substitution (0.1014 vs. 0.0871), and that synonymous substitution rates are higher in genes close to the breakpoints of individual rearrangements. The many potential causes of such striking are discussed, particularly in the light of speciation models suggesting that chromosomal rearrangements may have contributed to some of the speciation processes along the human and mouse lineages. Still, there are other possible causes and further research is needed to properly explore them.