Epigenetics
Study of heritable modifications that influence gene expression without altering the sequence.
📖 Full definition
Epigenetics is the field that studies how gene expression can be switched on or off without altering the underlying DNA sequence. The two main molecular mechanisms are DNA methylation — the addition of a methyl group to a cytosine nucleotide that silences the corresponding gene — and post-translational histone modifications. Histones are the proteins around which DNA is coiled; their chemical state determines whether a chromatin region is open (active gene) or condensed (silenced gene). What distinguishes epigenetics from classical genetics is its reversibility and sensitivity to the environment. Chronic stress, diet, pollutant exposure, physical exercise, and smoking all leave measurable epigenetic marks. Unlike a DNA mutation, these marks can change over a lifetime — a property called epigenetic plasticity. Transgenerational transmission is the most debated aspect: some epigenetic marks survive the reprogramming that occurs at fertilization and can be inherited across one to three generations. The Swedish Överkalix cohort study showed that the nutritional conditions of paternal grandparents during adolescence correlated with metabolic risk in their grandchildren. Mouse experiments have confirmed epigenetic transmission of stress responses across two generations. Longitudinal studies on monozygotic (genetically identical) twins reveal increasing epigenetic divergence with age. This explains how two people with identical genomes can develop different diseases, age differently, and display increasingly distinct phenotypes after 40 — directly relevant to the visible facial resemblance observed between members of the same family. In the context of family resemblance research, epigenetics adds a key layer: shared genes do not guarantee identical appearance, because environmental history shapes which genes are expressed.
💡 Concrete example
If your grandmother experienced severe famine during pregnancy, epigenetic marks may influence your metabolism today — without any change to your DNA. Similarly, identical twins raised in very different environments (one a smoker, the other not) can, by age 60, show methylation profiles different enough to be distinguished by a simple epigenomic analysis.
🔄 Synonyms
epigenetic regulation
🔗 See also
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