The role of DNA methylation in genetic expression is to regulate gene activity, often silencing or activating specific genes without altering the DNA sequence. This epigenetic modification involves the addition of a methyl group to the DNA molecule, which can affect how genes are expressed in various tissues and developmental stages. DNA methylation plays a crucial role in processes such as cell differentiation and response to environmental changes. Aberrations in methylation patterns are linked to various diseases, including cancer, making it an important area of research in understanding gene regulation and potential therapeutic interventions.