Accelerated evolution of genome sequences among phylogenetically diverged species with dN/dS ratio analysis

Abstract

dN/dS ratio has been widely used to estimate evolutionary acceleration of genome sequence. dN/dS is the ratio of non-synonymous substitution number in non-synonymous sites (dN) to synonymous substitution number in synonymous sites (dS). Synonymous substitution means mutations that make no difference in coding protein of the gene, and non-synonymous substitution means mutations making a difference in the coding protein. This estimator is used to measure accelerated evolution of orthologous genes of related species, which aimed to reveal evolutionary trend among phylogenetically diverged species. With comparing orthologs of six species, which were human, mouse, horse, dog, cow, and pig, I tried to find genetic evolutionary evidences supporting differences of monotocous and polytocous traits. These species were grouped into three monotocous and three polytocous species: human, horse, and cow as a monotocous group and mouse, dog, and pig as polytocous. In this study, I suggested some candidate genes supposed to correlate with evolutionary difference of the reproductive trait. Genes evolutionally accelerated in each group showed functional differences from functional annotation analysis, and dN/dS values were higher in orthologs of monotocous species than polytocous in general. I also performed dN/dS ratio analysis on ten primates including human to demonstrate genetic evolution related to brain functions. 41 genes were suggested from the analysis to go through accelerated evolution more in human than other nine primates. Functions of the genes represented possibilities of human evolution directed to improvement of memory and cognitive ability. And two of ten genes highly accelerated in human were associated neuronal disorder diseases, which also indicated evolution in human neuronal functions specifically.