Methylation is a biochemical process where a methyl group, consisting of one carbon atom and three hydrogen atoms (–CH₃), is added to a molecule, often DNA. This modification can influence gene expression without changing the underlying DNA sequence, playing a crucial role in regulating various biological functions. In the context of genetics, methylation can affect how genes are turned on or off, impacting traits and susceptibility to diseases. Environmental factors, such as diet and exposure to toxins, can influence methylation patterns, highlighting the interaction between epigenetics and the environment in shaping health outcomes.