1. Perelman School of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, 2 Computational Biology Program, Fred Hutchinson Cancer Research Center, Seattle, WA, 3 RainDance Technologies, Lexington, MA, 4 Pacific Biosciences, Menlo Park, CA and 5 Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York City, NY, USA