Department of Genetics, Stanford University, Stanford, CA 94305-9010, USA. coopergm@stanford.edu <coopergm@stanford.edu>|Department of Genetics, Stanford University, Stanford, CA 94305-9010, USA. coopergm@stanford.edu <coopergm@stanford.edu>|Department of Genetics, Stanford University, Stanford, CA 94305-9010, USA. coopergm@stanford.edu <coopergm@stanford.edu>