Epigenetics is about turning genes on or off. It’s also about doing this stably; a leopard doesn’t change its spots even if it sheds its fur each year. So epigenetics is about stable cellular memory that persists after cell division and, in some cases, even through sexual reproduction. Epigenetics, then, concerns the mechanisms that make organisms or parts of organisms look different, despite the fact they have the same genes and are in the same environment.

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Source: Explainer: what is epigenetics?