  Cells can often choose among several stably heritable phenotypes. Examples
are the expression of genes in eukaryotic cells where long chromosomal regions
can adopt persistent and heritable silenced or active states, that may be
associated with positive feedback in dynamic modification of nucleosomes. We
generalize this mechanism in terms of bistability associated with valleys in an
epigenetic landscape. A transfer matrix method was used to rigorously follow
the system through the disruptive process of cell division. This combined
treatment of noisy dynamics both between and during cell division provides an
efficient way to calculate the stability of alternative states in a broad range
of epigenetic systems.
