RESUMEN
The rodent subfamily Arvicolinae, which contains about 125 species, presents some interesting exceptions concerning Sry, the sex determining gene in mammals. In some species multiple Sry copies have been described on the Y chromosome and in the Iberian vole, Microtus cabrerae, several Sry sequences have been cloned and mapped not only on the Y but also on the X chromosome. Here we present a comparative analysis of Sry sequences from a total of 22 species. Our study demonstrates for the first time that for most North American species, as previously reported for the European species, multiple copies of the Sry gene exist on the Y chromosome. Furthermore, we have sequenced and analyzed the full sequence of Sry from several European species, showing that the sequence and structure of the gene in this group of species present the main features described for Sry in other mammals. Finally, FISH analyses on some of these species demonstrated that all Sry sequences, despite their functional status, mapped on the euchromatic short arm of the Y chromosome.