Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk|Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk|Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk|Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk|Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk|Department of Genetics, University of Cambridge, Cambridge, UK. r.auburn@gen.cam.ac.uk