Bistability is a phenomenon frequently observed in physics, chemistry, and biology, wherein a system exhibits two equilibrium states. These states persist even when subjected to arbitrarily small perturbations. Various systems, from climate change to the cell cycle, rely on bistability and the specific characteristics it entails.

For example, several key behaviors for the cell cycle result from bistability, including relaxation oscillations marked by a slow dynamic on the “low” and “high” states and a rapid shift between them. Observations of bistability are evident in interactions between cyclin B and cyclin-dependent kinase 1 (Cdk1) or the anaphase-promoting complex/cyclosome and the complex cyclin B-Cdk1. These proteins are crucial for regulating the cell cycle since they govern the transition between interphase and the mitotic stage.

It also manifests as hysteresis, where the coexistence of two states results in different transition points depending on directionality of the trajectory. Additionally, bistability contributes to the formation of traveling waves—connections between “high” and “low” states that move at a fixed velocity through space, enabling the faster and more reliable transportation of signals compared to mere diffusion.

As such bistability is the base for many biochemical models of cell division and thus is a frequently included feature of models developed and utilized in our lab.