FURTHER EXAMINATION OF THE KINETICS OF GONADAL DEVELOPMENT IN XY FEMALE MICE

Y-chromosomes derived from house mouse populations of Mus domesticus a re able to lead to the formation of XY females (i.e. hermaphrodite ind ividuals with both ovarian and testicular tissues) when inserted, by a ppropriate crosses, into the C57BL/6J genome, which usually carries th e Mus musculus Y chromosome. An abnormal interaction between the testi s-determining gene on the Y (of domesticus origin) and an autosomal re cessive allele (of musculus origin) needed for testicular formation is the likely explanation of this phenomenon. In the present paper we an alyse the histological kinetics of gonadal development in hermaphrodit es obtained by introducing the Y chromosomes from wild living house mi ce [from Zagreb, (Croatia) and Hohenentringen (Southern Germany)] into the C57BL/6J genome. Among 88 individuals, 9 XY hermaphrodites were d etected, 6 before birth and 3 afterwards. The percentage of the ovaria n-type tissues in the ovotestes fell drastically between day 18 of fet al life and day 20 after birth. These findings corroborate and extend those already published for other Y domesticus chromosomes and stress the possible role of Y chromosome differentiation in speciation proces ses.