Now-a-days, when we think of mutations, we’re likely to think of super heros, with fantastic abilities to swim under water or shoot lasers from their eyes. In reality genetic mutations occur all the time, and for the most part, go unnoticed.
A mutation means any change in DNA sequence. One commonly studied mutation is a single nucleotide change, from an A to a T, for example. Those are called SNPs, which stands for Single Nucleotide Polymorphism. There can also be very small insertions and deletions of only a few nucleotides. Those are called indels, which is short for insertion-deletion.
A mutation will only have an effect on the organism if it occurs in some functional area of the genome, and it needs to be the right type of mutation. A good analogy is baking a cake. There are lots of substitutions you can make and still end up with a cake. You can use carob instead of cocoa, hazelnut instead of walnut, almond extract instead of vanilla, brown sugar instead of white – and you’ll still get a great cake at the end. But there are some things that will really change the cake. People will notice raisins instead of chocolate chips, which may not be so bad, but substituting salt for the sugar, or leaving out baking soda and powder will result in something very unpleasant.
So there are different kinds of substitutions we can make when baking a cake, and the same goes for DNA. Geneticists often study non-synonymous mutations. These are SNPs that occur in a known gene and end up coding for a different amino acid in the resulting protein. An amino acid change has a good chance of having a functional consequence, so these types of mutations are likely important. They are also a favourite because we can predict amino acid changes, given only the DNA sequence. Synonymous SNPs, on the other hand are less interesting, because the resulting amino acid in the protein is the same. Even thou the DNA has changed, the end-product, that is the protein, is the same. Regardless of the typs of mutation, if the sequence has changed, it is considered a new allele.
The functional consequence of mutations that occur outside of genes are very difficult to determine. That’s because many regions of DNA control the behaviour of surrounding genes. Exactly how those genes are affected, or even if they are is the big question, but it is clear that they have a large effect.
Most mutations are considered neutral, but some can be quite negative, causing disease or death, and others can be beneficial. Each one of us has about 140 new mutations compared to our parents.
So while we generally want to avoid mutations, it’s good to know that they are constantly occurring, but for the most part don’t have any real effects.
