Practice question

Stem cell systems often maintain steady state through population asymmetry rather than invariant asymmetric division of every single cell synchronously. Individual stem cells stochastically adopt variable fates: some undergo symmetric self-renewal generating two stem cells, some undergo symmetric differentiation producing two committed progenitors, while overall population balance remains constant due to neutral competition and niche space limitation. Lineage tracing in mouse intestine, epidermis, and testis supports this probabilistic model. Consequently population-level equilibrium emerges without requiring each division to be strictly asymmetric, and niche signals modulate probabilities rather than dictate identical division rates.