Describing heritable changes that are not the result of changes in DNA sequence. An example of an epigenetic phenomenon is gene imprinting, in which expression of a gene varies depending on whether it is inherited from the mother or father. The chief mechanisms are chromatin remodelling, involving changes to the histone proteins that package DNA into chromatin, and DNA methylation, which causes widespread silencing of genes. In paramutation, which has been described in several plant species, certain genes behave as if they have undergone mutation after being in the same genome as other, so-called paramutagenic alleles. The change persists in subsequent generations of plants, even when the paramutagenic alleles are no longer present. Paramutation has also been described in mice; a possible explanation is that microRNAs transmitted from sperm to egg cell are responsible for silencing particular genes. See also epigenome; x inactivation.