Cell size distributions in lineages

Cells actively regulate their size during the cell cycle to maintain volume homeostasis across generations. While various mathematical models of cell size regulation have been proposed to explain how this is achieved, relating these models to experimentally observed cell size distributions has proved challenging. In this paper we present a simple formula for the cell size distribution in lineages as observed in e.g. a mother machine, and provide a new derivation for the corresponding result in populations, assuming exponential cell growth. Our results are independent of the underlying cell size control mechanism and explain the characteristic shape underlying experimentally observed cell size distributions. We furthermore derive universal moment identities for these distributions, and show that our predictions agree well with experimental measurements of E. coli cells, both on the distribution and the moment level.