Every stem cell division is a coin flip biased by signals from its niche (neighbouring support cells and growth factors like Wnt/Notch). Each event yields one of three outcomes:
p(self) = clamp(p_base + k · (niche − 0.5), 0, 1)
r < p(self) → symmetric self-renewal: 2 stem cells
p(self) ≤ r < p(self)+p_a → asymmetric division: 1 stem + 1 progenitor
r ≥ p(self)+p_a → symmetric differentiation: 2 progenitors
- Self-renewal probability — baseline chance p_base a division keeps both daughters as stem cells rather than committing them.
- Niche signal strength — models local growth-factor concentration; shifts the effective self-renewal probability up or down (a weaker niche pushes a tissue toward faster differentiation and exhaustion).
- Division mode — Symmetric-only mirrors expanding pluripotent/embryonic populations; Asymmetric-only mirrors adult tissue stem cells that keep the pool size constant while still producing progeny.
- Maturation rate — how quickly a progenitor (yellow) commits to a final lineage (neural/muscle/blood) once produced.
Real-world relevance: this same self-renewal/differentiation balance is what lets induced pluripotent stem cells (iPSCs) be expanded in culture, then coaxed into growing patient-specific organoids and cell therapies for regenerative medicine.