Why Your Genes Are Not Your Destiny

Tuesday, December 29, 2015. Author Dr Samantha Decombel


Genetic testing will be the next big thing in fitness. The analysis of a persons DNA to reveal their genetic secrets is one of the fastest growing industries worldwide. But there is a confounding factor to this, and it is called epigenetics.

Epigenetics: the fly in the ointment?

Epigenetics is a term that is often held up as a counter-argument to the use of genetic testing in sports. But what does it actually mean?

The word itself literally means ‘upon, or outside of, genetics’. It describes changes that affect gene expression that aren’t changes to the DNA code itself. As we grow and develop, carefully orchestrated chemical reactions activate and deactivate parts of our genome at strategic times and in specific locations. Epigenomic changes can be thought of as chemical tweaks to our DNA and to the proteins that package our DNA. The mechanism by which these chemical tags activate and deactivate genes is called epigenetics.

Chemical tweaking to our DNA code

There are different types of epigenetic marks, and each one tells the machinery in our cells to process those parts of the DNA they affect in certain ways.

One epigenetic change you may have heard of is methylation. This occurs when DNA is tagged with tiny molecules called methyl groups that attach to some of its ‘C’ letters. These methyl groups tend to prime a gene to be turned off, so it is no longer expressed.

Another type of change has more to do with the arrangement of DNA. DNA isn’t found in a big long endless line in your cells, its actually wrapped neatly around proteins called histones. The configuration of these histone packages and how close they sit together can affect which genes are read, and how many. For example, tightly wrapped sections of DNA tend to inactivate nearby genes, as it makes them unreadable, whereas if the DNA is more relaxed and the genes easily accessible, they are more likely to be active.

How does a muscle cell know to become a muscle cell?

There is an important reason why epigenetics is so important to us, and it’s pretty obvious when you think about it. Every cell in your body starts off with the exact same DNA sequence, give or take a few letters here or there. So, as you grow and develop, how does a muscle cell know it is supposed to be a muscle cell, and not a liver cell or a brain cell, if the information contained in the DNA is all the same?

You have around 20,000 genes contained in your DNA in total, all of which code for proteins with varying functions. As a developing embryo, you consisted of a small bundle of stem cells, which had the potential to express all of these genes and form each and every one of the different cell types.

As you grew, these cells differentiated – becoming specialised - and the genes that were expressed in each cell type changed. In differentiated cells, only around 10-20% of the total number of genes are actually active, and the sets of genes that are being expressed will be different between cell types. As I’m sure you’ll have realised by now, this is achieved by epigenetics: the addition of chemical tags in response to developmental signals that either activate the genes that are required, or deactivate those that are not.  

Your DNA code remains fixed for life, but the Epigenome is flexible

The really interesting thing about epigenetics is that the marks aren’t fixed in the same way that your DNA sequence is. They can change throughout your lifetime, and in response to outside influences.

After you’ve grown, signals from the outside world continue to play a role in shaping the gene regulation in your body via epigenetic changes. Factors like what you eat, how much you exercise and even social interactions create signals that travel from cell to cell throughout your body and stimulate these adaptations. As in early development, these signals continue to be important for many processes, including physical growth and fitness. There is even evidence from animal models that, while most epigenetic marks are removed from sperm and egg, some (as many as 1%) can be inherited.

What does this mean for genetic testing?

Our inherent genetic variation plays a very important role in defining our physiology, and physical strengths and limitations. Notwithstanding this, the environment we grow and live in will also define us, and can alter the way our genes are expressed. Epigenetics is the reason why identical twins, who share exactly the same DNA code, aren’t actually identical.

It is not nature vs. nurture as much as it is nature plus nurture.

Your genes are not necessarily ‘your destiny’ and if you change your environment through particular changes to your training and diet, you can significantly impact the way in which your genes are expressed, thereby improving your outcomes, whether that be getting stronger or reducing body fat. That’s not to say that genetic testing isn’t a useful tool. Your DNA code is the raw material on which the environment acts, and without this information you are missing a significant piece of the puzzle. However the genetic data should always be overlaid with the environmental data for the most accurate predictions. The take home message is that genetic data should never be considered in isolation, as factors such as your age, weight, diet or activity levels can be key to how your genes are interpreted.

There is no doubt that we are currently on the edge of a genetic revolution, one in which we will see massive advances in knowledge over the next 10-20 years. We are only just beginning to understand the full significance of our genes and the extent to which they influence our bodies. Understanding the relevance of epigenetics will be an important step in unlocking the mysteries of the genome.


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