Epigenetic management of the genome. An idealized chromosome is depicted with genes that are either transcribed (green) or silenced (red). As cells undergo developmentally-regulated changes in lineage (in either normal development or in the context of ES cell differentiation), patterns of gene expression change. Genes can be specifically silenced or activated through epigenetic means facilitated by chromatin remodeling (left lineage). Once terminally differentiated states are reached, patterns of gene expression can be maintained in a metastable fashion through maintenance of chromatin configuration (right lineage).