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- Title
Multiple Sex Chromosomes in the Marsupials.
- Authors
SHARMAN, G. B.; McINTOSH, A. J.; BARBER, H. N.
- Abstract
DURING the past thirty years, some twenty species of marsupials have been examined cytologically. In all of them, a typical XY sex-chromosome mechanism has been reported. We have recently re-investigated the potoroo (Potorous tridactylus), a common species of rat-kangaroo in Tasmania. In the spermatogonial mitoses, the male shows thirteen chromosomes, whereas the female shows twelve in ovarian mitoses (Figs. 1 and 2). The chromosomes of the female can easily be arranged in homologous pairs, one pair (the X-chromosomes) being conspicuous by their long, nearly median, centromere constriction. In the male, ten chromosomes can be paired, but three have no similar partners. These are the X, with a long submedian constriction, the smallest of the set (Y1), and an acrocentric (Y2). The last two chromosomes are not represented in the female. In accord with these observations, five bivalents held together by from one to five chiasmata and a trivalent are formed at the first division of meiosis in the male (Fig. 3). The trivalent is made up of the X, pairing in one of its arms with Y1, and in the other arm with Y2. Orientation on the spindle is always such that Y1 and Y2 are directed to one pole, and the X to the other pole. Two types of sperm are produced, a male-determining type with seven chromosomes, and a female-determining with six. The sex-determining mechanism is, thus, of the XY1Y2 : XX type.
- Publication
Nature, 1950, Vol 166, Issue 4232, p996
- ISSN
0028-0836
- Publication type
Article
- DOI
10.1038/166996a0