Sex Chromosome Mosaicism in Liver, Thymus, Spleen and Regenerating Liver of Perameles Nasuta and Isoodon Macrourus

Abstract

An X chromosome disappears from female cells and the Y chromosome disappears from male cells during development in some somatic tissues of the bandicoots P. nasuta and l. macrourus leaving the cells with a 2n = 13 (Le. XO) chromosome complement. In order to determine time of disappearance of the relevant sex chromosome, counts were made from dividing cells in liver, thymus and spleen of both species at various stages of development. Histological studies of liver and thymus were made at the same developmental stages. Frequencies of 2n = 14 cells (Le. those containing both sex chromosomes) were high in the liver and thymus of animals 1-4 days old but were low at 15 days of age when haematopoietic cells predominated. While most cells of thymus and spleen remained 2n = 13, the frequency of 2n = 14 cells rose again in the liver of animals aged over 20 days at which time blood-forming activity was considerably diminished. It is suggested that blood-forming cells of both species of bandicoot discard a sex chromosome at an early stage of differentiation.