title: The evolution of imprinting: chromosomal mapping of orthologues of mammalian imprinted domains in monotreme and marsupial mammals.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK. cae28@cam.ac.uk
authors.forename: Carol A
authors.initials: CA
authors.lastname: Edwards
authors.forename: Willem
authors.initials: W
authors.lastname: Rens
authors.forename: Oliver
authors.initials: O
authors.lastname: Clarke
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Mungall
authors.forename: Timothy
authors.initials: T
authors.lastname: Hore
authors.forename: Jennifer A Marshall
authors.initials: JA
authors.lastname: Graves
authors.forename: Ian
authors.initials: I
authors.lastname: Dunham
authors.forename: Anne C
authors.initials: AC
authors.lastname: Ferguson-Smith
authors.forename: Malcolm A
authors.initials: MA
authors.lastname: Ferguson-Smith
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial; D015342:DNA Probes; D019143:Evolution, Molecular; D018392:Genomic Imprinting; D017404:In Situ Hybridization, Fluorescence; D007614:Macropodidae / Q000235:genetics*; D010987:Platypus / Q000235:genetics*; D049951:X Chromosome Inactivation