Department of Computational Genomics, Wellcome Trust Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK.|Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK.|Department of Genetics, Harvard Medical School, Boston, MA 02135, USA.|Department of Computational Genomics, Wellcome Trust Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK.