Epigenetics is the study of how cells control gene activity without changing the DNA sequence."Epi-"means on or above in Greek,and "epigenetic" describes factors beyond the genetic code. Epigenetic changes are modifications to DNA that regulate whether genes are turned on or off. These modifications are attached to DNA and do not change the sequence of DNA building blocks. Within the complete set of DNA in a cell (genome), all of the modifications that regulate the activity (expression) of the genes is known as the epigenome.

Because epigenetic changes help determine whether genes are turned on or off, they influence the production of proteins in cells. This regulation helps ensure that each cell produces only proteins that are necessary for its function. For example, proteins that promote bone growth are not produced in muscle cells. Patterns of epigenetic modification vary among individuals, in different tissues within an individual, and even in different cells within a tissue. Environmental influences, such as a person’s diet and exposure to pollutants, can impact the epigenome. Epigenetic modifications can be maintained from cell to cell as cells divide and, in some cases, can be inherited through the generations.

A common type of epigenetic modification is called DNA methylation. DNA methylation involves the attachment of small chemical groups called methyl groups (each consisting of one carbon atom and three hydrogen atoms) to DNA building blocks. When methyl groups are present on a gene, that gene is turned off or silenced, and no protein is produced from that gene.

Another common epigenetic change is histone modification. Histones are structural proteins in the cell nucleus. DNA wraps around histones, giving chromosomes their shape. Histones can be modified by the addition or removal of chemical groups, such as methyl groups or acetyl groups (each consisting of two carbon, three hydrogen, and one oxygen atoms). The chemical groups influence how tightly the DNA is wrapped around histones, which affects whether a gene can be turned on or off.

Errors in the epigenetic process, such as modification of the wrong gene or failure to add a chemical group to a particular gene or histone, can lead to abnormal gene activity or inactivity. Altered gene activity, including that caused by epigenetic errors, is a common cause of genetic disorders. Conditions such as cancers, metabolic disorders, and degenerative disorders have been found to be related to epigenetic errors.

Scientists continue to explore the relationship between the genome and the chemical compounds that modify it. In particular, they are studying the effects that epigenetic modifications and errors have on gene function, protein production, and human health.