Any process that modulates the frequency, rate or extent of gene expression; the process is mitotically or meiotically heritable, or is stably self-propagated in the cytoplasm of a resting cell, and does not entail a change in DNA sequence. [ http://www.ncbi.nlm.nih.gov/pubmed/11498582 http://www.ncbi.nlm.nih.gov/pubmed/10521337 ]

A process that modulates the frequency, rate or extent of gene expression through chromatin remodeling either by modifying higher order chromatin fiber structure, nucleosomal histones, or cytosine methylation of DNA. Once established, this regulation may be maintained over many cell divisions. It can also be heritable in the absence of the instigating signal. [ http://www.ncbi.nlm.nih.gov/pubmed/11498582 http://www.ncbi.nlm.nih.gov/pubmed/34414474 http://www.ncbi.nlm.nih.gov/pubmed/10521337 http://www.ncbi.nlm.nih.gov/pubmed/22243696 ]