Dating evolutionary strata on the human sex chromosomes reveals complex history of X-Y recombination suppression

In mammals, distinct evolutionary strata – regions with similar X-Y divergence among sequences, but different from neighboring regions – evolved following a series of inversion events that suppressed recombination between the sex chromosomes. However, little is known about when these strata were formed. Here, using a phylogenetic method and taking advantage of the growing number of mammalian genome sequences, we present bounds of when X-Y recombination was suppressed across the X chromosome.