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Cytological studies of marsupial and monotreme cells in tissue culture

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Bick, YAE (1967) Cytological studies of marsupial and monotreme cells in tissue culture. PhD thesis, University of Tasmania.

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Abstract

Recent advances in cytological techniques have made it possible to
determine chromosome numbers of animals whose karyotype had not been
known with certainty because of large chromosome numbers and small size
of some of the chromosomal complement. The discovery by Nowellithat
phytohaemagglutinin (a protein with a mucopolysaccharide prosthetic
group, obtained readily as a crude extract from the common bean) can
initiate mitotic division in blood leucocytes cultured in vitro has made
it possible to determine the karyotype of an animal from as little as a
few drops of blood. Hypotonic treatment produces excellent spreads of
chromosomes without the use of squash techniques, and the addition of
colchicine for the final two hours of the culture period increases the
number of cells arrested at metaphase and further facilitates the determination
of chromosome numbers and morphology.
In placental mammals, chromosome numbers vary over a wide range
(from 18 to 86 for the diploid number), although the DNA content has been
found to be relatively constant for all species. Marsupials are characteriZed
by large chromosomes and small numbers (2n = 10 to 22), but the DNA
content and volume accord with those of eutherian mammals.
Little information has been recorded about the chromosomes of the
monotremes. The karyotype of the platypus has been investigated by Matthey (1949) although with the techniques available at that time the
chromosome number (70 ±10) could not be ascertained with accuracy.
Matthey remarked that the karyotype in the monotrines shows a division
into macro and micro elements and is similar to that in birds and
reptiles. Van Brink (1959) published a report on the karyotype in
Echidna giving numbers for the male between 62 and 64. She recorded
one large chromosome as being unpaired, but the scarcity of divisions
in the material available did not allow for a decision between an X0
and XY heterogamety.
In most mammalian species studied there is a typical XX-XY sex
chromosome mechanism, and the male is the heterogametic sex. However,
there is an XX-XY1 Y2 mechanism in two macropod marsupials, Potorous
tridactylus and Wallabia bicolor, and at least one eutherian
mammal, Sorex araneus. A, more complex sex-determining system,
X1X1X2X2 in the female andX 1X2Yin the male, has been found in two
placental mammals and recently in an Australian marsupial, the hare wallaby. The sex-determining system in the Monotremata is completely unknown.
In this work an attempt has been made to resolve the sex-determining
system of the monotremes and to determine their karyotype. Metaphases
from colchicine-treated short-term cultures of leucocytes from
the peripheral blood of the male and female echidna and platypus gave
suitable preparations from which the chromosome number could be determined
without ambiguity. In addition, chromosome spreads from two male echidnas were obtained by subjecting testis material to trypsinization and hypotonic treatment for examination of mitosis and meiosis in spermatogenesis.
The testes of the male platypus available for this study were
small and undeveloped and no divisions were found. Good chromosome
preparations were obtained, however, from the spleen of the female
platypus.
Both the monotremes are highly protected species. Although the
platypus and echidna are much more common in Tasmania than in other
Australian states, the platypus is rarely seen, and presents a further
problem since it often dies of shock after a few hours in captivity.
The breeding season, about which little information is available, is of
short duration; and the scarcity of divisions in the gonads, which often
regress for considerable periods, make the study of testicular meiosis
extremely difficult without sacrificing large numbers of animals.

Item Type: Thesis (PhD)
Keywords: Cytology, Tissue culture
Copyright Holders: The Author
Copyright Information:

Copyright 1967 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Appendix includes published article: Y. A. E. Bick , W. D. Jackson, 1967, A Mammalian X-O sex-chromosome system in the monotreme tachyglossus aculeatus determined from leucocyte cultures and testicular preparations, American naturalist, 101(917), 79-8 © American naturalist. This is an open access journal. Other published articles have been excluded.

Date Deposited: 25 Nov 2014 00:41
Last Modified: 24 Aug 2016 00:54
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