Further examination of the kinetics of gonadal development in XY female mice.

Y-chromosomes derived from house mouse populations of Mus domesticus are able to lead to the formation of XY females (i.e. hermaphrodite individuals with both ovarian and testicular tissues) when inserted, by appropriate crosses, into the C57BL/6J genome, which usually carries the Mus musculus Y chromosome. An abnormal interaction between the testis-determining gene on the Y (of domesticus origin) and an autosomal recessive allele (of musculus origin) needed for testicular formation is the likely explanation of this phenomenon. In the present paper we analyse the histological kinetics of gonadal development in hermaphrodites obtained by introducing the Y chromosomes from wild living house mice [from Zagreb, (Croatia) and Hohenentringen (Southern Germany)] into the C57BL/6J genome. Among 88 individuals, 9 XY hermaphrodites were detected, 6 before birth and 3 afterwards. The percentage of the ovarian-type tissues in the ovotestes fell drastically between day 18 of fetal 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 processes.