https://www.nature.com/articles/npp2012112
https://en.wikipedia.org/wiki/DNA_methylation
https://www.frontiersin.org/articles/10.3389/fgene.2019.0019...
And both can be modified by changes in the environment and diet.
https://www.nature.com/articles/npp2012112
https://en.wikipedia.org/wiki/DNA_methylation