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The standard definition of epigenetics requires these alterations to be heritable, either in the progeny of cells or of organisms.

The term also refers to the changes themselves: functionally relevant changes to the genome that do not involve a change in the nucleotide sequence.

The similarity of the word to "genetics" has generated many parallel usages.

When Waddington coined the term, the physical nature of genes and their role in heredity was not known; he used it as a conceptual model of how genes might interact with their surroundings to produce a phenotype; he used the phrase "epigenetic landscape" as a metaphor for biological development.These epigenetic changes may last through cell divisions for the duration of the cell's life, and may also last for multiple generations even though they do not involve changes in the underlying DNA sequence of the organism; One example of an epigenetic change in eukaryotic biology is the process of cellular differentiation.During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells.Epigenetic changes modify the activation of certain genes, but not the genetic code sequence of DNA.The microstructure (not code) of DNA itself or the associated chromatin proteins may be modified, causing activation or silencing.