Sex-chromosome mosaicism in pouch young of marsupials Perameles and Isoodon

Abstract

In 0- to 2-day-old bandicoots (Perameles nasuta and Isoodon obesulus) both sex chromosomes were retained in all skin and gut cells examined. Elimination of one X chromosome had occurred in some spleen cells and in all liver cells examined in a 10-day-old female P. nasuta. In a 24-day-old male I. macrourus the Y chromosome was absent in all (three only) spleen cells examined and in more than half of the liver cells. Both X chromosomes were present in all corneal cells of a 55-day-old female I. macrourus, but in the same animal only one X was present in all spleen and bone-marrow cells examined. Sex-chromosome elimination in bandicoot tissues occurred at much later stages of morphogenesis than does the appearance of sex-chromatin bodies in the cells of eutherian mammal embryos. Thus sex-chromosome inactivation probably occurs much later in bandicoots than it does in eutherian mammals.