Comparative chromosome painting between two marsupials: origins of an XX/XY1Y2 sex chromosome system
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Cross-species chromosome painting was used to investigate genome rearrangements between tammar wallaby Macropus eugenii (2n = 16) and the swamp wallaby Wallabia bicolor (2n = 10♀/11♂), which diverged about 6 million years ago. The swamp wallaby has an XX female:XY1Y2 male sex chromosome system thought to have resulted from a fusion between an autosome and the small original X, not involving the Y. Thus, the small Y1 should represent the original Y and the large Y2 the original autosome. DNA paints were prepared from flow-sorted and micro-dissected chromosomes from the tammar wallaby. Painting swamp wallaby spreads with each tammar chromosome-specific probe gave extremely strong and clear signals in single-, two-, and three-color FISH. These showed that two tammar wallaby autosomes are represented unchanged in the swamp wallaby, two are represented by different centric fusions, and one by a tandem fusion to make the very long arms of swamp wallaby Chromosome (Chr) 1. The large swamp wallaby X comprises the tammar X as its short arm, and a tandemly fused 7 and 2 as the long arm. The acrocentric swamp wallaby Y2 is a 2/7 fusion, homologous with the long arm of the X. The small swamp wallaby Y1 is confirmed as the original Y by its painting with the tammar Y. However, the presence of sequences shared between the microdissected tammar Xp and Y on the swamp wallaby Y2 implies that the formation of the compound sex chromosomes involved addition of autosome(s) to both the original X and Y. We propose that this involved fusion with an ancient pseudoautosomal region followed by fission proximal to this shared region.
KeywordsCentric Fusion Chromosome Painting Tammar Wallaby Tandem Fusion Comparative Chromosome Painting
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- Ferguson-Smith MA (1995) Gene order by FISH and FACS. In Molecular Biology and Biotechnology. A Comprehensive Desk Reference, R.A. Meyers (ed) (VCH Publishers, Inc.), pp 354–359Google Scholar
- Graves JAM, Cooper DW, McKenzie LM, Hope RM, Watson JM (1993) Genetic maps of marsupial and monotreme mammals. In Genetic Maps. Locus Maps of Complex Genomes, S.J. O’Brien (ed) (Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratories Press), pp. 4.282–4.289Google Scholar
- Hayman DL, Martin PG (1974) Mammalia I: Monotremata and Marsupialia. In Animal Cyotgenetics, 4 Chordata, B. John (ed) (Berlin, Stuttgart: Gebrüder Borntraeger), pp 000–000Google Scholar
- Rofe RH (1978) G-banded chromosomes and the evolution of Macropodidae. Aust Mammal 2, 53–63Google Scholar
- Toder R, Wienberg J, Voullaire L, Maccarone P, Graves JAM (1997) Shared DNA sequences between the X and Y Chromosome in the tammar Wallaby-evidence for independent additions to eutherian and marsupial sex chromosomes. Chromosoma (in press)Google Scholar