1. Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.
2. Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
3. Committee on Genetics, Genomics and Systems Biology, University of Chicago, Chicago, IL 60637, USA.
4. Department of Genetics, Stanford University, Stanford, CA 94305, USA.
5. Department of Biology, Stanford University, Stanford, CA 94305, USA.