1. Epigenetics Programme, Babraham Institute, Cambridge CB22 3AT, UK.
2. Centre for Trophoblast Research, University of Cambridge, Cambridge CB2 3EG, UK.
3. European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Genome Campus, CB10 1SD Hinxton, Cambridge, UK.
4. European Molecular Biology Laboratory, Genome Biology Unit, Heidelberg 69117, Germany.
5. Wellcome Trust Sanger Institute, Cambridge CB10 1SA, UK.