Department of Statistics, The Pennsylvania State University, University Park, PA, USA.|Department of Population Health Sciences, Medical College of Georgia, Augusta University, Augusta, GA, USA.|Department of Biology, The Pennsylvania State University, University Park, PA, USA.|Department of Statistics, The Pennsylvania State University, University Park, PA, USA.|Department of Statistics, The Pennsylvania State University, University Park, PA, USA.|Wellcome Trust - MRC Cambridge Stem Cell Institute, University of Cambridge, Cambridge, UK.