Question: What is a mutation?

Ciarán O'Brien answered on 21 Nov 2014:

A mutation is a change in the code of someone’s DNA, big or small.

So DNA is a long molecule containing a genetic code for the bits and pieces that make you up. The code is spelled by the 4 nucleotides adenine, guanine, thymine and cytosine, or A,G,T, and C for short.

So a small part of your DNA might read ACGGTT, and it might code for something like your eye colour. If that bit of DNA got damaged, it’s usually repaired quickly and without a fuss. Very, very rarely though, your body makes a mistake while repairing and you might end up with that piece of DNA reading ACGGTA, the last nucleotide being an A when it used to be a T. That’s a mutation, and most of the time it does nothing. That little mutation MIGHT affect your eye colour, if every cell in your eye got the same mutation at the same time, but chances are it’s harmless, and each time the cell divides, the new cells will carry that mutation.

That’s how mutations build up, lots of harmless little changes that don’t really affect your body, that get passed on to your children, but together can add up to change things over generations, especially when those changes provide a benefit of some kind for the environment you live in.

Some mutations aren’t harmless though. If one of your cells gets a mutation that stops an important gene from working, that cell will usually just die before it can divide and spread the mutation. If you’re unlucky, the change will cause the cell to grow out of control and you get cancer.

Over time, mutations can cause entire new species to emerge. It was only a few years back that scientists discovered a new species of bacteria that could eat nylon. Since humans only invented nylon in the last 80 years or so, that shows how quickly mutation can build up when it gives an evolutionary advantage to a species!