Evolutionary steps of sex chromosomes are reflected in retrogenes.

It has been shown that selective pressure to compensate for the silencing of the sex chromosomes during male meiosis resulted in many X-linked genes being duplicated as functional retrogenes on autosomes. The silencing of male sex chromosomes was probably stratified during evolution, in accordance with their stratified diversification. Here I show that the timing of the retrocopying events is associated with the timing of the X-Y differentiation of the region of the X chromosome housing the parental copy of the gene.