1. Department of Genetics, Stanford University, Stanford, CA 94305, USA.
2. Medical Research Council (MRC) Centre for Causal Analyses in Translational Epidemiology, School of Social and Community Medicine, University of Bristol, Oakfield Grove, Bristol BS8 2BN, UK.
3. Department of Bioengineering and Therapeutic Sciences and Medicine, University of California San Francisco, San Francisco, CA 94143, USA.
4. Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D04103 Leipzig, Germany.
5. Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA.
6. Department of Plant and Animal Sciences, Nova Scotia Agricultural College, Truro, Nova Scotia B2N 5E3, Canada.