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What is DNA methylation?

DNA methylation is when methyl groups are added to a strand of DNA which can regulate the activity of the DNA without changing the sequence by turning the DNA “on” or “off”.

How does DNA methylation occur?

Methylation of DNA occurs when an enzyme, known as a DNA methyltransferase, adds a methyl group to a cytosine base in the DNA sequence. This addition of a methyl group can affect the expression of the gene by turning the gene on and off. 

Where does DNA methylation take place? 

A specific part of DNA, the cytosine base, is where DNA methylation has been found to occur. This takes place in the nucleus of the cell, where DNA is located. 

How does DNA methylation affect gene expression?

DNA methylation can cause a gene to be turned “on” or “off.” When DNA is methylated, it typically turns the gene off, causing it to not be expressed. When DNA is demethylated, it turns on, causing the gene to be expressed. This change in gene expression without changing the DNA sequence is known as epigenetics.

Learn more about DNA Methylation:

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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