Figure 1. Modeling the effects of both intrinsic and extrinsic noise.

(A) A schematic of the Telegraph process, with nodes $A$ (active) and $I$ (inactive) representing the state of the gene. Transitions between the states $A$ and $I$ occur stochastically at rates μ and λ, respectively. The parameter $K$ is the mRNA transcription rate, and δ is the degradation rate. (B) The compound model incorporates extrinsic noise by assuming that parameters θ of the Telegraph model vary across an ensemble of cells, according to some probability distribution $f(\theta ;\eta )$. (C) Variation in the parameters across the cell population leads to greater variability in the mRNA copy number distribution.