More than a decade ago, fluorescent reporter studies highlighted the
stochastic nature of gene expression, and biologists then began to examine the phenotypic heterogeneity they saw in clonal cell populations, through they chalked up what they saw to noisiness in gene expression. Still, researchers wondered about the cause of the randomness they had observed. Now, biophysicists and systems biologists are looking into that question and aim to figure out how and why single cells and molecules behave the way they do, and the consequences of that behavior.