Before revision:  Here we consider the simplest unit of gene regulation ,  the repressed gene, which is instead characterized by nonlinear dependencies on external parameters , leading to corresponding nonlinear extrinsic noise.
After revision:  Here we consider the simplest unit of gene regulation , non-white, and nonlinear poses serious limitations to its general applicability. Here we revisit the fundamental features of linear Gaussian noise, pinpoint its limitations, and review recent new approaches based on nonlinear bounded noises, which highlight novel mechanisms to account for transitions to bimodal behaviour. We do this by considering a simple but fundamental gene expression model, the repressed gene, which is instead characterized by nonlinear dependencies on external parameters , leading to corresponding nonlinear extrinsic noise.