  In this work we propose a model for gene expression based on the theory of
random dynamical systems (RDS) and show that it has a "modularity property" in
the following sense: given any collection of genes that are linked in a
transcriptional network, if each of them is individually described by a certain
class of RDS then there is a natural, and essentially unique, prescription for
coupling them together, respecting the network topology, in such a way that the
collective system formed by all genes is a RDS as well. Moreover, the class of
RDS used to describe the individual genes is flexible enough to account for a
wide range of stochastic behaviors within the realm of stationary processes.
