An Autoradiographic Study of DNA Synthesis in the Sex Chromosomes of Two Marsupials with an XX/XY1Y2Sex Chromosome Mechanism

Abstract

Potorous tridactylus and Protemnodon bicolor are marsupial species in which the sex chromosome system is XX/XY1Y2. Nearly all the long arm of the X is homologous with the Y2; the short arm of the X is unpaired in the male. During the last part of DNA synthesis in females only the short arm of one of the 2 X-chromosomes shows asynchronous synthesis of DNA. The long arm sof the X’s and homologous autosomes synthesize DNA synchronously. Some pairs of non-homologous autosomes synthesize asynchronously. The implications of this in terms of the Lyon hypothesis and the evolution of X-chromosomes are discussed.