Fig. 2.

An illustrative sequence of mutations (occurring every 100 days) in the saturating feedback model (feedback model 2). The initial parameters are taken to be α = 0.286, α₂ = 0.3, β = 0.432, β₂ = 0.3, γ = 0.323, k₀ = 0.1, m₀ = 0.1, k₁ = 0.01, and m₁ = 0.01. The mutations cause, successively, β = 0.512, α = 0.5, β = 0.697, β = 1.1. For β = 1.1 there is no steady state and unbounded growth occurs.