1. Department of Biosystems Science and Engineering, ETH Zurich, 4058 Basel, Switzerland; 2SIB Swiss Institute of Bioinformatics, 4058 Basel, Switzerland; 3European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire, CB10 1SA, United Kingdom; 4Wellcome Trust Sanger Institute, Hinxton, Cambridgeshire, CB10 1SA, United Kingdom; 5Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge, CB20RE, United Kingdom