Let’s use a practical example: Imagine the ADAM12 gene, which participates in processes important for neuroplasticity (the brain’s ability to create new connections). It has a variant called rs4962322, where a certain allele is associated with greater potential for intelligence and brain plasticity in studies. Suppose a person has a genotype that includes this advantageous allele.
But what if she lived for years in a poor environment, with little reading, few new stimuli, high stress, and a poor diet? This lifestyle can generate epigenetic markers that “silence” the gene. The result: even having the beneficial allele in the DNA, the body ends up functioning as if it weren’t there. The genetic potential remains dormant in practice.
In epistasis, the interaction occurs between the genes themselves: the effect of one gene is influenced by the presence of another.
Now imagine the CLOCK gene, which helps regulate sleep and the internal biological clock. It has a known variant (rs1801260), where certain alleles are linked to more stable and better quality sleep. Suppose the person has the favorable genotype for this variant, that is, they have a genetically good “sleep architecture”.
This proper functioning of the CLOCK gene can interact epistatically with the ADAM12 gene. Quality sleep acts as a booster: it creates a better internal environment (more brain recovery, less inflammation, greater ability to form connections), causing the advantageous allele of ADAM12 to produce even more neuroplasticity. It’s as if one gene “talks” to and helps the other to perform at its best!
