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Epigenetics (literally; outside genetics) refers to changes in the way genes are expressed. These are not due to changes in the actual sequence of DNA, rather they are small chemical modifications to some parts of the DNA double helix or to the proteins that are bound to DNA.

Scientists have discovered that small chemical modifications to DNA itself and to the proteins (called histones) that DNA is wound around, can turn expression of genes on and off. These chemical modifications include the addition of methyl groups to some of the DNA components and also addition of methyl and other chemical groups to histone proteins associated with the DNA.

Some of these epigenetic changes happen as part of the process of development from an embryo into an adult. Internally regulated epigenetic changes are involved in the control of the carefully synchronised expression of different genes during growth.

The single cell that results from the fusion of a father’s sperm with a mother’s egg divides repeatedly and eventually creates the many different types of cells that make up our bodies. All the cells in our body have the same DNA within them but different cell types such as kidney, brain or muscle cells look and function in their own ways because different genes are expressed in different cell types.

However, other epigenetic changes are caused by external factors such as our environment. Populations that are quite homogeneous but exposed to different environmental conditions over time such as famine, will produce generations of children and grandchildren that are different in their susceptibility to conditions such as obesity and diabetes and this can influence people’s health and longevity.

 During our lives, the choices we make about our lifestyle will also produce epigenetic changes to our DNA and histones and affect gene expression. This can result in protection from or susceptibility to things such as heart disease and cancer. One example is smoking which has been shown to produce epigenetic changes in our DNA. Studies have shown that genes that increase the risk for cancer and diabetes, or are important for the immune response or sperm quality, are affected by smoking. It is very likely that these epigenetic changes are a factor in the increased risk of these conditions that smoking causes.

Epigenetics is creating a lot of interest because it is a way of explaining how we might be changed by the environment in which we live and then pass these characteristics on to future generations. The vast majority of epigenetic changes are erased during the formation of egg and sperm cells and very soon after the sperm and egg fuse to form a fertilized egg. However, a few epigenetic changes are passed down to our offspring. We are now learning that not all inheritance is due to the genes coded by our unique DNA sequence. Some epigenetic changes that are caused by the things we experience or do are passed on to our children and grandchildren.

As well as the innate and external causes of epigenetic changes described above, it is now known that some inherited diseases are due to mutations that affect the epigenetic machinery. Two different diseases; Prader-Willi and Angelman syndromes are due to mutations in the same gene, but which condition is present depends on whether the mutation is inherited from the child’s mother or the father. More information about these conditions can be found in links 2 and 3 below.
 
More information can be found by following these links:

  1. What is epigenetics 1?  Very simple explanation.
  2. What is epigenetics 2? More detailed explanation.
  3. Wikipedia – epigenetics Very detailed article.
  4. Simple YouTube video explaining epigenetics
  5. Video explaining epigenetics from the Garvan Institute
Last Review Date: November 14, 2017