[1] Univ Nottingham, Queens Med Ctr, Inst Genet, Nottingham NG7 2UH, England
[2] Univ Edinburgh, Ctr Genome Res, Edinburgh EH9 3JQ, Midlothian, Scotland
[3] Univ Oxford, Dept Biochem, Canc Res Campaign Chromosome Mol Biol Grp, Oxford OX1 3QU, England