Stochastic model of HSC behavior.²⁶  HSCs in the stem-cell reserve have 3 potential fates: replication (1 HSC becomes 2 HSCs), differentiation (1 HSC becomes 1 STRC), or apoptosis (1 HSC becomes 0). These occur at average rates of λ, ν, or α, respectively. The maximum number of HSCs in the stem-cell reserve is K. If an HSC differentiates, then it enters the second compartment and contributes to hematopoiesis (becomes an STRC). The average length of time from differentiation until the clone ends its contribution is μ.