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The word "epigenetics" shows up in articles about health everywhere. But what does it really mean?

Epigenetics has become one of the hottest specialties in biological science. It's a genetic phenomenon that has powerful effects on each of us throughout our lives, and it may even explain how we transmit genetic "memories" of our life experiences to our children, grandchildren, and great-grandchildren. But epigenetics is not the end-all of scientific understanding or the answer to every health questions.

A Workable Epigenetics Definition

What is epigenetics, anyway? If you were to read most articles on genetics, even some written by genuine scientists of genuinely respected credentials you might conclude the definition is something like this:

  • Epigenetics explains why identical twins aren't completely identical.
  • Epigenetics explains that my great-grandmother's struggle to get food in World War II is the reason I'm fat now.
  • Epigenetics explains why some people can't help cheating on their spouses.
  • Epigenetics explains why I got lung cancer, not my smoking.

In short, epigenetics is often used as an explanation for (1) things that we just don't understand or (2) things we don't want to blame on something else. But at least on a biological level, epigenetics is something entirely different.

Epigenetics Is Information Overlaid on DNA

Epigenetics is basically additional information added to DNA. If you thought of DNA as an instruction manual, epigenetics would be the highlighted sections of the text. A user could highlight important sections in red and less important sections in blue, as if to say, "Be sure to follow this," but "Don't pay as much attention to that." Those highlighted sections stay with the text even if the book is photocopied, although the colors may not come through. 

Something similar happens with DNA. Every cell in our body has the same sequence of A, C, G, and T bases, but not every cell does the same thing. DNA in the strand can be tagged with methyl groups (-CH3) that attach themselves to the "C" (cysteine) bases. This process is known as DNA methylation. Methylation is like the blue highlighter in the instruction manual, telling the user "You don't need this right now."

Epigenetics and the Histones

Have you ever wondered why DNA is coiled like a helix? Or how it stays that way?

Another set of actors in epigenetics are the histones. These are proteins that act as a kind of spacer between the strands of DNA. Together with DNA they make up microsomes, which look something like strings of pearls under electron microscopy.

Histones attract methyl groups. Because DNA is helical, sometimes this makes a segment of DNA more exposed. This in effect activates a gene. Sometimes it makes a segment of DNA less exposed. This in effect deactivates a gene.

Turning genes on and off makes sense in terms of cellular function. A brain cell, a fat cell, and a muscle cell all have the same DNA, for instance, but they don’t have the same functions. Different genes are activated in the different kinds of cells.

Turning genes on and off also makes sense in terms of life history. If your grandmother nearly starved in World War II, even if you were born in 1985, your genes for fat storage may be turned on in 2016. Your DNA prepares gives you a head start on dealing with your environment, although your genes may not get the message that your world is different from your grandmother’s.

Epigenetics explains how we are pre-programmed to deal with changing life conditions. Your DNA stays the same throughout life, but different parts of it are activated or deactivated.

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