European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK. rh497@cam.ac.uk|European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK. rh497@cam.ac.uk|European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK. rh497@cam.ac.uk