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Open Access Highly Accessed Research article

The evolution of imprinting: chromosomal mapping of orthologues of mammalian imprinted domains in monotreme and marsupial mammals

Carol A Edwards1, Willem Rens2, Oliver Clarke2, Andrew J Mungall3, Timothy Hore4, Jennifer A Marshall Graves4, Ian Dunham3, Anne C Ferguson-Smith1* and Malcolm A Ferguson-Smith2

Author Affiliations

1 Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK

2 Cambridge Resource Centre for Comparative Genomics, Department of Veterinary Medicine, University of Cambridge, Cambridge CB3 OES, UK

3 Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK

4 Research School of Biological Sciences, The Australian National University, Canberra, Australia

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BMC Evolutionary Biology 2007, 7:157  doi:10.1186/1471-2148-7-157

Published: 6 September 2007

Abstract

Background

The evolution of genomic imprinting, the parental-origin specific expression of genes, is the subject of much debate. There are several theories to account for how the mechanism evolved including the hypothesis that it was driven by the evolution of X-inactivation, or that it arose from an ancestrally imprinted chromosome.

Results

Here we demonstrate that mammalian orthologues of imprinted genes are dispersed amongst autosomes in both monotreme and marsupial karyotypes.

Conclusion

These data, along with the similar distribution seen in birds, suggest that imprinted genes were not located on an ancestrally imprinted chromosome or associated with a sex chromosome. Our results suggest imprinting evolution was a stepwise, adaptive process, with each gene/cluster independently becoming imprinted as the need arose.