This article first appeared in Issue 7 of our free digital magazine CURIOUS.
If you’ve ever taken a high school biology class, you might well fancy yourself an accomplished geneticist. Why are your eyes blue? Genes. Why is your hair curly? Genes, duh. We’re taught early on that our traits are predetermined by our DNA, by the genes we inherit from our parents. Even our predisposition to certain health conditions, we’re told, is written into our genetic code. This idea that our “genetic destiny” is sealed before we’re even born permeates much of our education and understanding of genetics.
Two alleles for brown eyes and BAM, you’ve got yourself a pair of chocolate-colored peepers. Inherit a copy of a gene that puts you at risk of cancer and you’ll likely go on to develop it. Simple. Except it isn’t.
“Contrary to what you might think, your genetic destiny is not preordained,” writes Aubrey Milunsky in his 2001 book Your Genetic Destiny: Know Your Genes, Secure your Health, Save Your Life. “Despite our genetic blueprints, there is much we can do to secure our health – and even to save our lives or those of our loved ones.”
Of course, genes do have an important role to play, but, as it turns out, the tale we’re spun in school is a super watered-down version of things. It’s so much more than just DNA, which makes sense really – such a fundamental thing as determining our genetic destiny should, rightfully, be pretty complicated to explain.
But we’re about to try. Allow us to introduce you to the world of epigenetics.
What is epigenetics?
Epigenetics is the study of changes that affect gene expression (the process by which instructions in DNA are converted into a functional product e.g. protein) without actually altering the DNA sequence.
The clue is in the name: “epi” is a Greek word meaning “in addition”. In this case, it means in addition to the genome – factors beyond the genetic code that can affect an organism’s observable characteristics, their phenotype.
So while genes are busy underpinning our physical traits, epigenetics is busy tinkering with our DNA. Epigenetic changes can affect how our bodies “read” a DNA sequence, effectively turning genes “on” and “off” as they please.
Epigenetic changes are intrinsically linked to our behaviors and environment: things such as diet and exercise can sometimes result in epigenetic changes that could alter gene expression. They are also reversible since the DNA sequence itself remains unchanged.
How does epigenetics modify DNA?
That’s all well and good but what does it actually mean? The DNA sequence is exactly the same and yet these mysterious “changes” can completely overhaul how it’s expressed: it’s confusing, to say the least.
DNA is made up of four bases – adenine, cytosine, guanine, and thymine, (A, C, G, and T) – which are essentially its “code”. Epigenetic changes don’t mess with this code in the sense that they don’t alter the sequence of bases, but they do affect the DNA molecule in several ways.
One of these ways is methylation, the process of adding a chemical group – a methyl group, hence the name – to DNA. When added at the right place on the DNA molecule, these groups can prevent proteins from binding to, and therefore “reading”, the DNA.
Another type of epigenetic change is histone modification. Histones are proteins that interact with DNA and help to package it into chromosomes. When DNA is tightly packed around multiple histones it is less accessible to the “reading” proteins and so will not be expressed. By adding or removing chemical groups to histones, epigenetics can change how DNA interacts with them and turn genes “off” or “on”.
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“Known epigenetic changes [also] include changes to gene expression during embryogenesis [embryo development], which can lead from a single undifferentiated, fertilized egg to a whole range of different cell types and tissue types (brain, heart, muscle, other organs) in the developing embryo,” David Scott Wishart, Distinguished University Professor in the University of Alberta’s Departments of Computer Science and Biological Science, told IFLScience.
These, and numerous other epigenetic changes, all influence gene expression over the course of our lifetimes and contribute to our genetic destiny.
Causes of epigenetic changes
As for why these changes happen, there are myriad reasons, Wishart explained.
“Epigenetic changes arise through the action of chemical or protein gradients within cells (in the case of embryogenesis) or through the actions of chemicals, proteins or small RNA fragments (siRNA, miRNA) that lead to reversible changes in DNA structure or changes in how DNA is read or transcribed.”
“Epigenetic changes can also arise from oxidation of DNA (via chemicals) or the expression of certain proteins or RNA fragments that interfere with gene expression,” Wishart added.
And, as we hinted at earlier, the environment can occasionally play a part in this.
“Some of these effects can be due to stress, diet, exposure to certain chemicals, exposure to viruses or bacteria, or the presence of certain proteins. Overall, epigenetic changes reflect environmental effects on the genome.”
However, Wishart is quick to add, this is pretty rare.
“Many environmental exposures do not lead to epigenetic or genetic changes. So it’s important to note that environmental exposures are only occasionally converted to epigenetic events. The environment affects much more than DNA and some of these effects are much more profound and significant for health and disease than epigenetic or mutagenic events.”
Effects of epigenetics
As we’ve established, epigenetic changes can have a profound effect on gene expression and, therefore, on our genetic destiny. But what exactly does this look like? How, specifically, do these changes impact our development, our phenotype, our health?
Our epigenetic changes can influence our offspring, and maybe even “grandoffspring”, too, making them dictators of destiny across generations.
According to Wishart, epigenetics is fundamental in human embryo development: it plays a key role in the formation of our limbs and organs, and in the differentiation of our cells and tissues.
In adults, it can play a part in the development of disease, including obesity, cancer, heart disease, and diabetes. “These diseases are all ‘environmental’,” Wishart explained. “They can be caused by poor diet, but the diet also modifies the expression of genes so that even if someone reverts to a healthy diet, the epigenetic changes may still persist and may even be passed on to other generations.”
Our epigenetic changes can influence our offspring, and maybe even “grandoffspring”, too, making them dictators of destiny across generations.
And they don’t just impact the destiny of our species. In the animal kingdom, epigenetic changes can affect the sex determination of turtles, which is dependent on temperature. And in the plant world, they have a part to play in flowering time, for example.
Genetics vs epigenetics vs something else?
When it comes to destiny, we know genetics is important. And we know epigenetics shouldn’t be overlooked either. But which is weighted heavier on the genetic fate scales?
“The genetic code is more important for determining your destiny than epigenetics,” says Wishart. “However genetics and epigenetics only play a minor role in your overall destiny or overall phenotype.”
While our genes may be, to an extent, a blueprint for our traits, they are not some kind of congenital crystal ball that will reveal what lies in our future.
So, what then, if not genetics or epigenetics, has the final say?
“The direct effects of your environment, your diet, your lifestyle, your microbiome, your exposure to bacteria or viruses and other non-genetic and non-epigenetic factors play a much bigger role in determining your health, your quality of life, or how long you will live.”
These things, Wishart told us, are part of the “exposome” – a measure of all the things an individual is exposed to in their lifetime and how they relate to health. They don’t act on DNA, instead affecting our proteins, cells, tissues, or organs.
According to Wishart, just 5 percent of deaths or diseases can be accounted for by our genes. “The other 95 percent of deaths are a result of what you’ve been exposed to. Bacteria and virus infections cause about 30 percent of all cancers, exposure to fire smoke or air pollution kills tens of millions of people due to direct damage to lung tissues, overeating (obesity) causes most cases of heart disease, stroke, and diabetes.”
While our genes may be, to an extent, a blueprint for our traits, they are not some kind of congenital crystal ball that will reveal what lies in our future. DNA does not necessarily predict our destiny, and not just because of epigenetics. It turns out the exposome has a lot to answer for. But, thankfully, that is something it may be possible for us to control.
“It’s hard to change your genome, it’s easy to change your exposome,” said Wishart. “That’s why your destiny is in your hands, your destiny is not in your DNA.”
CURIOUS magazine is a digital magazine from IFLScience featuring interviews, experts, deep dives, fun facts, news, book excerpts, and much more. Issue 10 is out now.
Source Link: Does Your DNA Predict Your Destiny?