THE KARYOTYPES OF 2 SOUTH-AMERICAN MOUSE OPOSSUMS OF THE GENUS THYLAMYS (MARSUPIALIA, DIDELPHIDAE), FROM THE ANDES, AND EASTERN PARAGUAY

The karyotypes of Thylamys macrura, from eastern Paraguay and adjacent Brazil, and T. pallidior, from the Andean Altiplano in Argentina and Bolivia, are reported for the first time. The karyotypes of somatic ti ssues from female T. macrura and female T. pallidior consist of 2N = 1 4. However, the diploid number found in somatic cells in males of T. p allidior exhibits 2N = 13 because the Y chromosome is missing. The mis sing Y phenomenon might represent another case of chromosome mosaicism in American marsupials, although this time detected in didelphids.