Abstract
Clonal populations of cells exhibit substantial phenotypic variation. Such heterogeneity can be essential for many biological processes and is thought to arise from stochasticity or intrinsic regulation in signal transduction and gene expression. Only recently have advances in single-cell analysis enabled detection of dynamic changes in transcription and biological signals at the systems level. The connection between different layers of cell-to-cell heterogeneity may reveal how it is harnessed to regulate cell-fate choice.