Illustration of a two-checkpoint drift-diffusion+threshold model of the cell cycle.

<p>Simulation was performed by numerically solving <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192087#pone.0192087.e001" target="_blank">Eq 1</a>, twice in sequence, using the Euler-Maruyama algorithm [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192087#pone.0192087.ref056" target="_blank">56</a>] with a fixed time step Δ<i>t</i> = 0.01. Drift and diffusion constants are <i>μ</i>₁ = <i>μ</i>₂ = 0.2 and <i>σ</i>₁ = <i>σ</i>₂ = 0.1, respectively.