Epigenetics is the study of a group of mechanisms that cells use to turn genes on or off, or to turn a gene’s activity (also called gene expression) up or down. There is also an element to these mechanisms that involves a memory of how a cell’s parent, grandparent, or even further back has expressed these genes.
One popular analogy for the interplay between genetics and epigenetics is to think of the human body as a computer. DNA is the hard drive and the epigenetics is the software which is driving the computer. The software tells the hard drive which tasks to perform and when but without the hard drive the software would have nothing to run on.
Our hard drive (the genome) begins in just one cell (a fertilized embryo) but to make a complete human that cell will need to give rise to trillions of cells that can be broken down into dozens of discrete types (i.e. neurons, immune cells, skin, etc.). Each cell type has an unique role and function. The cells of your skin are very different than the cells of your immune system, and both of these are very different than those that function in the endocrine system. The proper functioning of these different types of cells is necessary to serve the larger goal of maintaining a healthy person.
Yet despite the differences in functioning, every one of these cells has in it a complete and distinct human genome that carries all the instructions that are necessary for a functioning human. Furthermore, every cell has a 2 copies of every gene one from mom and one from dad. Suffice it to say, for a microscopic entity such as a cell, that’s a lot of genetic material to have to keep track of. This is where epigenetics plays a vital role. There are at least 19,000 genes in the human genome but each cell only needs a small subset of this massive instructional booklet.
Epigenetic modifications are one-way cells package their copy of the entire genome in a way that allows only the genes necessary to that cell type to be accessible. These processes (you can read ELP’s articles on the major epigenetic modifications: Methylation, non-coding RNA, Histone Modifications and Chromatin Remodeling) either create physical barriers to access genes for cellular machinery or physically pack the DNA in ways that close off certain regions or open them. The memory of this packaging is often passed on from one cell to its daughter cells, in this way your body can ensure that when new cells are made they function the similarly to the parent.
As you can imagine, epigenetics plays an important role in developmental biology. The term derives from ‘epigenesis’ coined by Aristotle to describe his theory of how living things developed. During his time, many subscribed to the theory of preformation which states that living things begin as miniature versions of themselves. Aristotle’s epigenesis theory was founded on the idea that organisms developed incrementally. Later, developmental biologist Conrad Waddington incorporated the term into the discussion of the mechanisms by which an organism’s genes gave rise to its appearance.
However, in recent years epigenetics has expanded as some studies have found that environmental factors–like diet, exercise, climate change, psychological trauma–can also drive the placement of epigenetic factors and thus the expression of certain genes. Some have taken this to mean that epigenetics represents how nurture (environment) effects nature (genes and gene expression). One of the most prominent studies of this was done with rats, where researchers found changes in gene expression linked to the amount of nurturing the rats received as pups.
Another aspect that has been added to the study of epigenetics in recent years is the idea that epigenetic changes, often those derived from environmental exposures, exhibit transgenerational inheritance at the organism level–from parent to offspring and possibly beyond. For example, descendents of victims of the Dutch Hunger Winter showed evidence in their epigenome (the collection of epigenetic markings on a person’s genome) of the traumatic event. In humans this is supported mostly by data from epidemiological studies, but in other organisms like plants, the data is far more robust that these acquired changes can be passed onto future generations.
However, others argue that neither of these aspects are due to epigenetics. Some have suggested that the variations we see in epigenetics (that are attributed to some exposure to an environmental factor) are actually the result of genetic variation from person to person. Other experts believe that epigenetics are the artifacts or consequences of other processes, meaning targeting them or “fixing them” won’t change a person’s health.
The on-going debate over the significance of epigenetics and the role it plays in humans and all life on earth makes it one of the most exciting fields of study in science.