[1] European Bioinformat Inst, Hinxton CB10 1SD, Cambs, England
[2] Natl Res Council Canada, Inst Informat Technol, Ottawa, ON K1A 0R6, Canada
[3] Univ Cambridge, Cambridge Inst Med Res, Cambridge, England
[4] Univ Hertfordshire, BioComputat Lab, Hatfield AL10 9AB, Herts, England
[5] Wellcome Trust Sanger Inst, Hinxton, England