A population of cells shows bimodal protein distributions from intrinsic transcriptional noise
Two-state promoter model (Peccoud-Ycart 1995): gene switches between ON (transcribing) and OFF states with rates k_on, k_off. Proteins produced in bursts during ON state. When k_off ≫ k_on, bimodality emerges — cells commit to either high or low expression states, explaining phenotypic heterogeneity without genetic differences.