Tracking the fate of individual cells and their progeny by clonal analysis has redefined the concept of stem cells and their role in health and disease. The maintenance of cell turnover in adult tissues is achieved by the collective action of populations of stem cells with an equal likelihood of self-renewal or differentiation. Following injury stem cells exhibit striking plasticity, switching from homeostatic behavior in order to repair damaged tissues. The effects of disease states on stem cells are also being uncovered, with new insights into how somatic mutations trigger clonal expansion in early neoplasia.BC and PHJ are supported by a core grant from the Wellcome Trust to the Wellcome Trust Sanger Institute. PHJ acknowledges support from a Cancer Research UK Programme Grant (C609/A17257).This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.ceb.2016.07.00
