  Cellular behavior is governed by gene regulatory processes that are
intrinsically dynamic and nonlinear, and are subject to non-negligible amounts
of random fluctuations. Such conditions are ubiquitous in physical systems,
where they have been studied for decades using the tools of statistical and
nonlinear physics. The goal of this review is to show how approaches
traditionally used in physics can help in reaching a systems-level
understanding of living cells. To that end, we present an overview of the
dynamical phenomena exhibited by genetic circuits and their functional
significance. We also describe the theoretical and experimental approaches that
are being used to unravel the relationship between circuit structure and
function in dynamical cellular processes under the influence of noise, both at
the single-cell level and in cellular populations, where intercellular coupling
plays an important role.
