A unique late-replicating XY to autosome translocation in Peromyscus melanophrys.

We report on the characterization of the Peromyscus melanophrys karyotype and sex chromosome system. Classic studies reported the sex chromosome system of this species may be as complex as an X(1)X(1)X(2)X(2)/X(1)X(2)Y(1)Y(2) and provided conflicting identification of the X chromosome. Using Peromyscus maniculatus chromosome paints, we have positively identified the sex chromosomes and clarified the sex determining system that once perplexed Peromyscus researchers. The sex chromosomes are characterized by a unique autosomal translocation of DNA shared between both the X and Y chromosomes. The translocated material is late replicating and heterochromatic yet retains the active chromatin conformation. Thus, autosomal regions derived from translocations involving repeat-rich material may retain some epigenetic marks specific to the sex chromosomes despite loss of epigenetic silencing activity.