Genetics / Science

Above genetics

What is the difference between epigenetics and genetics?

Thanks to Jess from Twitter for the question! Epigenetics is something that’s fascinated me for a long time, and I definitely recommend Nessa Carey’s book, The Epigenetics Revolution, if you want to read about it in more depth.

Most readers are probably familiar with genetics already: all living creatures have a genetic code made of DNA, which is shared to a great extent between members of the same species, and to a lesser but significant extent with members of related species. For example, chimpanzees and bonobos share a lot of DNA, and often suffer from the same diseases because of that similarity. DNA stands for deoxyribonucleic acid, and is stored within the nucleus of almost every living cell. It’s a versatile recipe book which codes for every single process a living organism requires, even though it’s ultimately built up from just four nucleic acids: adenine, cytosine, guanine and thymine. The specific series of these bases spells out proteins, and proteins do all the work in your body from moving your limbs to digesting your food.

The double helix of DNA: a sugar backbone joined by bases A (adenine), T (thymine), C (cytosine) and G (guanine).

Some of the differences between people are spelt out at this level of the genetic code. I might have a section of bases like ATG-GCA-GGG, which would spell out a simple protein made of the amino acids tyrosine, arginine and proline, in that order. If someone else had the sequence ATG-GGG-GCA in that spot, they’d make a protein made of tyrosine, proline and arginine, in that order. The proteins formed would be of different shapes, and might do different things in the body.

However, even if I had an identical twin with the exact same genetic code, we might have differences in the amount of protein we produced. This is caused by epigenetics — “epi” just means “upon”, so epigenetics consists of modifications made above the level of the genetic code. There are a few different epigenetic mechanisms; one example is methylation. This means that a methyl group, CH3, gets added to the DNA. This tells a cell not to bother making as much of that protein, and it’s more like a dimmer switch than an on-or-off switch. The amount of methylation dictates how much protein is made: if there’s a lot, very little protein will be made. This allows the body to respond to things in the environment: if a certain protein isn’t useful to you, your cells can methylate it so that your body doesn’t waste energy making it — but it’s still there for you to use again later if the need arises.

A big argument about epigenetics at the moment is to what extent epigenetic modifications can be passed between generations. If there’s one area where you can expect to see a lot of movement in biology, epigenetics is it. It might hold the keys to treating all kinds of diseases, suppressing cancers, and explaining complex differences between people. It’s an exciting area!

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