It is likely that everybody has heard of genetics, the study of the genes that determine our inherited traits, but perhaps not everybody is familiar with epigenetics.
Rather than concerning genes, epigenetics studies what is happening beyond them, with ‘epi’ literally translating to ‘on top of ’ in Greek. This means that although every one of our cells contain the exact same genetic material, not all of it is expressed in all cells. This is why nerve cells are long and have a branched structure and muscle cells contain muscle fibers. Epigenetics is the study of how and why genes are switched on oroff, leading to different gene expression patterns between cells and organs.
However, these patterns are not fixed, but alterable in response to changes
in circumstances. There are many interesting cases in wild animals, where this alteration in fact acts in favour of the given animal leading to adaptation to the environment.It is widely known, for example, that in many reptiles and amphibians sex is determined by external temperature. In turtles, this is due to a certain hormone that is able to convert the male sex hormone testosterone into the female sex hormone oestrogen. It also happens to be temperature sensitive; that is, at high temperature it gets activated and by producing oestrogen switches on genes involved in ovary formation. On the other hand, at low temperatures the hormone doesn’t work, and leaves testosterone which leads to testes formation.
Although this might seem strange to us, it is not as strange as the case of a Caribbean fish species, the blue-headed wrasse. This animal determines its sex depending on whether it encounters a male individual of its own species. If it does, then it becomes female and joins the ‘harem’ of that male, otherwise it becomes male. When the male of this group eventually dies, the largest female grows testes and replaces him.
We shouldn’t forget, however, that these transformations are not voluntary from the fish, but due to a range of biochemical interaction ending in the change of gene expression. The last example is taken from another group of animals: insects. The desert locust lives in Africa and can cause billions of dollars of damage in agriculture, spanning many countries during upsurgence, such as the ones written in the Bible and the Qur’an. These outbreaks, however, cannot occur at any time; the insects are normally short-winged and solitary. It is the increase in population density (when individuals can sense that they are too crowded), that causes a change in gene expression and leads to the emergence of longer, bright-coloured wings and migratory behaviour.
Apart from curious cases from wildlife, there is increasing evidence showing that epigenetics has a role in human diseases. A notable example of these is cancer, even though it has long been thought to be a condition of genetic origin.
Cancers often develop when a cell gains advantage in growth and reproduces itself very rapidly, leading to the formation of a tumor. Some researchers suggest that this advantage can arise not only from a gene mutation, but also from a healthy set of genes being turned on and off in an unhealthy pattern. Perhaps this turning on and off is mediated by environmental factors, for example molecules that we take in through eating which directly affect gene expression. Although all the genetic material (the genome) of the human body has been decoded, what happens to these genes in the process of epigenetic change is still something to uncover.
Epigenetic research is therefore one of the major focuses of science in the 21st century, having the potential to fight the big killers of our society, as well as contributing to conservation and producing more productive agricultural systems.