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Letters to Nature
Nature 432, 913-917 (16 December 2004) | doi:10.1038/nature03021; Received 17 June 2004; Accepted 8 September 2004; Published online 24 October 2004
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In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes
Frank Grützner1, Willem Rens2, Enkhjargal Tsend-Ayush1,4, Nisrine El-Mogharbel1,4, Patricia C. M. O'Brien2, Russell C. Jones3, Malcolm A. Ferguson-Smith2 & Jennifer A. Marshall Graves1
- Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, Australian Capital Territory 2601, Australia
- Centre for Veterinary Science, Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
- Department of Biological Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia
- These authors contributed equally to this work
Correspondence to: Frank Grützner1 Email: frank.gruetzner@anu.edu.au
The sequences reported in this paper have been deposited in EMBL under accession numbers AJ744847, AJ744848, AJ744849.
Abstract
Two centuries after the duck-billed platypus was discovered, monotreme chromosome systems remain deeply puzzling. Karyotypes of males1, or of both sexes2, 3, 4, were claimed to contain several unpaired chromosomes (including the X chromosome) that form a multi-chromosomal chain at meiosis. Such meiotic chains exist in plants5 and insects6 but are rare in vertebrates7. How the platypus chromosome system works to determine sex and produce balanced gametes has been controversial for decades1, 2, 3, 4. Here we demonstrate that platypus have five male-specific chromosomes (Y chromosomes) and five chromosomes present in one copy in males and two copies in females (X chromosomes). These ten chromosomes form a multivalent chain at male meiosis, adopting an alternating pattern to segregate into XXXXX-bearing and YYYYY-bearing sperm. Which, if any, of these sex chromosomes bears one or more sex-determining genes remains unknown. The largest X chromosome, with homology to the human X chromosome, lies at one end of the chain, and a chromosome with homology to the bird Z chromosome lies near the other end. This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.
- Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, Australian Capital Territory 2601, Australia
- Centre for Veterinary Science, Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK
- Department of Biological Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia
- These authors contributed equally to this work
Correspondence to: Frank Grützner1 Email: frank.gruetzner@anu.edu.au
The sequences reported in this paper have been deposited in EMBL under accession numbers AJ744847, AJ744848, AJ744849.
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