Epigenetics vs. Genetics

Epi – meaning over/above – genetics is the study of factors that affect DNA blueprint and gene expression, other than changes in the DNA sequence. The science of genes (genetics) is completely disregarded in epigenetics.

People tend to think that we are born with a concrete and unchanging DNA blueprint. This is untrue. Scientists and epigenesists have shown us, through experiments, that mechanisms other than those within the DNA sequence (known as epigenetics) will affect the activity of a gene and override some of the principles of genetics. For example – put simply – that our genes determine our physiology and chemical behavior.

Consider the following experiment:

The agouti mouse has a specific gene, which sources the reason for the mouse’s yellow fur and its obesity. Agouti mice are therefore very prone to diseases such as cardiovascular disease and diabetes.

This particular gene is passed onto future generations through reproduction, and therefore so are the agouti mouse’s traits. Hence, all agouti mice will have yellow fur and be obese.

The above represents the conclusion drawn from geneticists.

However, mechanisms such as methylation[1] can cause gene suppression, without altering the underlying DNA sequence. They do this by changing the positioning of regulator proteins[2] on the DNA, and can consequently activate or deactivate genes in the DNA strand. From the viewpoint of an epigenesist, this would stop the effect of the agouti gene, thereby overruling the genetic ideals involved.

The scientists performing the experiment took two groups of agouti mothers. One group was given methyl-rich supplements; the other was given nothing.

The offspring of the agouti mice that had not been given anything was as expected – yellow fur and overweight. The young of the agouti mice that took the supplement and underwent methylation differed to the other group in physiology and appearance. They had a normal brown coat, and were very lean. Nevertheless the gene responsible for agouti traits had been inherited.

 

This experiment helps to explain and to prove to us how our DNA blueprint is variable and changing, according to environmental factors (sometimes ambiguous). The methyl supplement given to one of the two groups of mothers altered their DNA blueprint, causing the deactivation of the agouti gene. So effectively, yes, the gene was passed on to their offspring, and yes, the offspring also inherited their DNA blueprint. However it was not the original blueprint, and the expected characteristics that usually follow the presence of the gene were not observed.

Humans and mice contain approximately the same number of genes – 24 000. Yet we are far more complex organisms than mice. Therefore, the answer as to why that is cannot lie in the make up and abundance of the genes, but rather what genes inside us are activated that perhaps are not in mice (and vice versa). From this we can draw that genes cannot be the structures that control us; we should focus instead on understanding how they are or aren’t put into play.

On a separate note (relevant nonetheless), the supposed big breakthrough when the two genes responsible for breast cancer (BRCA1 & BRCA2) were discovered proved to be less helpful than we thought – only 5% of breast cancers are hereditary. The other 95% occur as a result of environmentally induced mechanisms involved in epigenetics.


[1] The addition of a methyl-rich supplement to a substrate, or the substitution of an atom by a methyl group. In this case, we are referring to the methylation of DNA.

[2] Regulator proteins are a particular type of protein found on the DNA. When they cover a specific strand of the DNA molecule (a gene), that gene is tightly bound and latent. Methylation causes the shifting of the regulator proteins, thus activating the gene underneath.

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