Blurred Lines: Nature vs Nurture

dna

Emma Bryan explains that the foods you eat, the amount of sleep you get, the attitude you adopt could affect your own genes – and even the genes of your great-grandchildren. (As seen in Pegasus Pages, March 2014)

DNA is a brilliant molecule. In just about three billion base pairs, it can code for the (approximately) 250,000 proteins in the human body, as well as the three types of RNA required to synthesize these proteins. But if the genome itself wasn’t clever enough, attached to every DNA molecule are sets of chemical “tags” that determine the extent of coiling of the DNA molecule, and therefore which genes are expressed and which proteins formed. Collectively, they are known as the epigenome.

Research in this field is relatively recent, but the findings could change the way we look at inheritance completely. The thing about the epigenome is that, unlike your DNA code, it can be changed again and again throughout your life. This may mean that it is not just what genes you are born with, but also how those genes have been modified through lifestyle choices that are passed on to your children. Therefore what you eat and drink today, the amount of sunlight you get, the places you go, the attitude you adopt – all these can affect your epigenome, and potentially that of your children and grandchildren.

For example, correlation has been found between processed, chemical-filled foods and cancer – and this risk-factor can be passed on between generations. Increased amount of nitrites in foods could affect the epigenome itself, preventing certain genes from being expressed – in fact, the genes that code for programmed cell death. This means the cells become malignant. However current research into the mechanisms of the epigenome could reveal a way to promote genes that code for cell death and suppress cancer cell replication, perhaps another step towards the ultimate cure.

So how does it work? The epigenomic “tags” which are attached to the DNA helix are structures such as methyl groups, which attach to certain genes and alter their expression. One way they can do this is by acting as gene regulators, blocking RNA polymerase from transcribing the gene. (For non-biologists, RNA polymerase is the enzyme which copies the genetic code in a process called transcription, so that proteins can be built from it.) The other way that these “tags” work is that when there are large numbers of methyl groups on a certain area of the helix, they cause the helix to become tightly coiled, and therefore inaccessible to the RNA polymerase enzyme. This means they can’t be transcribed and proteins built from them – they become invisible. Conversely, a shortage of methyl groups causes the helix to unwind, and become easily accessible for copying.

Some methyl groups, which attach to the base cytosine, are permanent and are passed between generations. Others change according to chemicals in surroundings. Chronic stress for example, would promote high levels of stress hormones (e.g. cortisol) to be released, and this could change the positions of methyl groups on the genome. Some drugs work in the same way – anabolic steroids, for example, cause the DNA helix to uncoil more in areas that code for muscular proteins, increasing transcription in these areas, and therefore meaning that more muscular protein is formed. Hormones such as growth hormone work in a similar way.

All cells in our body are specialized, and the epigenome is simply the mechanism that regulates this. Stem cells differentiating in the embryo to form specialized cells results in permanent fixtures in the epigenome, which is what causes a nerve cell to be a nerve cell and not a white blood cell, even though the DNA each of them contain is identical.

Another thing that epigenetics could change is the evolution theory. As of now, we have believed that evolution happens purely through the selectively favourable characteristics an organism is born with being passed on to the next generation. However since the epigenome can be altered according to surroundings, perhaps organisms can in fact acquire characteristics during their lifetime, which can be passed on.

Experiences of neglect as a child could impact on the chemical makeup of their brain, and leave imprints on their genetic material that will never leave them. And these can be passed down through generations – for example Jews whose ancestors were survivors of the Holocaust could carry with them more than simply stories.  So in the nature versus nurture debate, epigenetics seems to suggest that nurture has an equal, if not larger, role to play in a person’s personality. In fact, perhaps there is no longer a difference between what is nature and nurture, as your epigenome is fashioned from a collection of your ancestors’ experiences.

Image: by Josh*m on Flickr (CC BY-NC-SA 2.0)

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