Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.|Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.|Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.|Center for Bioinformatics, School of Life Sciences, Peking University, Beijing, China.|Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.|Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.