In mammals, sex is determined by the action of the testis-determining gene on the Y chromosome, SRY, which directs the differentiation of the indifferent male gonad into a testis. In the absence of a Y chromosome, and SRY, the indifferent gonad follows the default pathway and differentiates as an ovary. The determination of gonadal sex is pivotal to the sexual differentiation of the individual, as subsequent sexual development is mediated by the gonadal hormones. The European mole presents an intriguing contrast to this general mammalian pattern in that all XX females possess ovotestes.
There is an annual growth and regression of these tissues, with ovarian follicular tissue predominating during the spring breeding season and testicular-like tissues composing the bulk of the ovary during the autumnal nonbreeding season. The proliferation of testicular-like tissues in the autumn ovary is the inverse of the pattern observed in the male mole, where testicular and androgen-dependent tissues develop in the spring and regress in the autumn. buy cipro
Recently, the presence of ovotestes has been described in an additional three species of the genus Talpa: T. occi-dentalis, T. romana, and T. stankovici.