Single cell heterogeneity that exists in a hPSC population. (A) Genetic heterogeneity can be caused by karyotypic abnormality, copy number variation, and point mutations within a hPSC population. (B) Major epigenetic heterogeneity in hPSCs occurs in DNA methylation, parental imprinting, and X chromosome inactivation. (C) Asynchronous cell cycle stages across individual cells and G1 length variation establish a major single cell heterogeneity in a hPSC population. (D) Positional heterogeneity distinguishes cells in the center of hPSC colonies from ones in the periphery. Differences in cell adhesion, receptor localization, and N-cadherin expression contribute to functional heterogeneity in a hPSC colony.