When we hear the word mutation, it conjures to mind hideous images of human-fish hybrids that might come swimming away from Chernobyl, animals with two heads and Caesar from Planet of The Apes. But in reality, mutations can be much more subtle than that. Mutations can happen on such a small level that you can’t even tell they’ve happened; they’re not always caused by radioactivity or toxic substances. Mutations are the mechanism behind evolution, and the reason behind cancer and certain hereditary diseases. Geneticists use the word mutation to describe a change to an organism’s genetic code, which can sometimes cause a change to their physical appearance, behaviour, health and a variety of other genetically-determined traits, and these changes can either occur in a single individual, or can be heritable mutations, meaning they can be passed on to their offspring.
Before I go into what we really mean when we talk about a mutation, here’s a brief reminder of what the “DNA code” is. We can look at the DNA code as a language, and in fact, this analogy works quite well, since we refer to the DNA bases which determine a person’s DNA sequence as either A, T, C or G bases. The way a sequence of these bases is organised gives us a different word, or in the case of genetics, we gain an amino acid for every three bases we put together, and the type of amino acid depends on which bases are used and in which order. Before the amino acid is formed, a translation process must first occur to translate these three letters into an amino acid. After this is done, amino acids join together to form a protein, which can have a different function, depending on which amino acids it is made up of and in which order.
During the process of translating this code, or in copying the code (the code is copied frequently, in order for new cells to be made in our bodies, for growth, repair and replacement of old cells), errors can occur (similarly to if you’re typing a long essay, you’re likely to make one or two typos). Two of the types of mutation that can occur in DNA are:
- Insertion/deletions: when one of the bases of the code is deleted, or an extra bases is added in. These kind of mutations can cause a big change to a protein, and also its function, often resulting in a complete loss of function of the protein, as they affect all the amino acids after the insertion/deletion occurs
- Substitution: when one bases is changed to another. A lot of the time this has no effect, or causes only a very small change to a protein
- There are also other types of genetic mutation, including inversion of sequences, which reverses the order of a segment of DNA.
So in biology, when we say “mutation” we don’t mean people growing extra body parts, tails, gills, fingers; we mean a tiny change to the DNA code (sometimes only one base out of the three billion that exist in each cell in the human body!), which can lead to a change in a protein, and sometimes but not always, a much greater change in a person of organism. Mutations are the reason that there is so much diversity in the human race. Over time, mutations accumulate and are passed on. Sickle cell anaemia is caused by a genetic mutation, changing the structure of red blood cells, so that they no longer function as well as they should. As James McAvoy’s character, Charles Xavier remarked in the film, X-men: First Class, “heterochromia”, or having one eye a different colour to the other is the result of a mutation, which changes the concentration of a hormone called melanin, which determines eye colour. Certain types of cancer are caused by mutations in genes which usually halt growth of cells at an approprite level. When these genes stop functioning correctly, cells divide more rapidly and in an uncontrollable manner, and the mass of cells created this way causes a tumour.
Mutations which are passed on to offspring can spur evolution and genetic variation in populations. If a mutation occurs which causes a physical change, this can either help or hinder an organism’s survival. If the change is advantageous, such as giving them immunity to a disease or making them faster or stronger so more capable of catching prey and avoiding predators, the individual is more likely to survive for long enough to reproduce, and the more they are able to reproduce, the more likely the trait is to be passed on to their offspring and then passed on for many more generations to come until it becomes much more common in the whole population. Other traits, which are neither advantageous or problematic can also arise due to mutations and be passed on, potentially accounting for the variety of hair colours and eye colours in humans, which may have arisen due to mutations a very long time ago in an ancient ancestor.
So while mutations can be harmful, they can also be neutral or go unnoticed. Without random mutations occurring in our ancestors, humans may not exist, as the mutations which give us the appearance and characteristics that we have now, may never have come to exist. In terms of genetics, who we are now is determined by a combination of mutations which occurred in our ancestors, and have been passed on to us, making us different from other primates, and different one another. Mutations are the carrier of change, whether to an individual or to an entire species. They’re not just for science-fiction and horror films, they’re a part of our history, and may even determine our future, whether that involves being able to fly and read minds, or not.