XY females in Microtus cabrerae (Rodentia, Microtidae): a case of possibly Y-linked sex reversal.

Microtus cabrerae is a species with blocks of heterochromatin on both sex chromosomes. Polymorphism caused by extensive deletions affecting these heterochromatic segments exists in both X and Y chromosomes. Of a total of 22 males and 22 females studied, four females exhibited sex pair dimorphism similar to that observed in males. C-banding techniques and preliminary data regarding inheritance support the hypothesis that these specimens are XY fertile females and that this sex reversion is most likely inherited through the Y chromosome of these females.