Adaptive evolution in the Per gene family of vertebrates: neofunctionalization by positive Darwinian selection after two major gene duplications

Gene duplication and subsequent functional divergence of the descendant genes is a primary source for the emergence of evolutionary novelties. Functional divergence after gene duplication, through the operation of positive selection, can result in neofunctionalization, that is, one copy acquires a novel function. Period genes are among the master genes of circadian rhythms that are governed physiologically and behaviorally by the endogenous clock. Gene targeting experiments showed functional divergence among the three clusters of this gene family. Using molecular evolution study tools, we provided strong support for experimental findings regarding functional divergence and we also found that the members of this family have experienced episodes of positive Darwinian selection (adaptive evolution) in their evolutionary history that have resulted in obtaining new functions, that is, they have experienced neofunctionalization. Furthermore, we hypothesized that Per2 genes may be functionally more important than Per1 genes.