Epigenetics is the study of changes in gene expression that do not involve a change in the base sequence of DNA. These changes can be passed on when cells divide, and sometimes from parents to offspring.Epigenetic changes are caused by chemical groups, often called epigenetic marks or tags, attached to DNA or to the histone proteins that DNA is wrapped around. The two main types are:
• DNA methylation: methyl groups added to cytosine bases in DNA
• histone modification: groups such as acetyl or methyl groups added to histones.These marks change how tightly DNA is packed, and whether transcription factors and RNA polymerase can reach a gene. This switches genes on or off without changing the genetic code. The full set of epigenetic marks in a cell is called its epigenome.The environment can change the epigenome
Diet, stress, smoking, toxins and other factors can add or remove epigenetic marks. This helps to explain how the environment affects phenotype. For example, identical twins have the same DNA, but as they get older their epigenomes become increasingly different, and they may develop different diseases.Epigenetic inheritance
When a cell divides by mitosis, its epigenetic marks are usually copied to the daughter cells. This keeps specialised cells, such as liver cells, expressing the right genes. Some marks may also be passed to the next generation. Studies of people conceived during the Dutch famine of 1944 to 1945 found epigenetic differences and health effects that lasted into later life.Unlike mutations, epigenetic changes can be reversed.
• DNA methylation: methyl groups added to cytosine bases in DNA
• histone modification: groups such as acetyl or methyl groups added to histones.These marks change how tightly DNA is packed, and whether transcription factors and RNA polymerase can reach a gene. This switches genes on or off without changing the genetic code. The full set of epigenetic marks in a cell is called its epigenome.The environment can change the epigenome
Diet, stress, smoking, toxins and other factors can add or remove epigenetic marks. This helps to explain how the environment affects phenotype. For example, identical twins have the same DNA, but as they get older their epigenomes become increasingly different, and they may develop different diseases.Epigenetic inheritance
When a cell divides by mitosis, its epigenetic marks are usually copied to the daughter cells. This keeps specialised cells, such as liver cells, expressing the right genes. Some marks may also be passed to the next generation. Studies of people conceived during the Dutch famine of 1944 to 1945 found epigenetic differences and health effects that lasted into later life.Unlike mutations, epigenetic changes can be reversed.