Question: how do DNA sequences mutate and evolve?

Bethany Dearlove answered on 22 Jun 2014:

Great question! A mutation is just a change in the DNA sequence – from ACTGCT to ACCGCT, for example. These changes can appear during cell copying when a mistake is made and the wrong nucleotide (A, C, T or G) is added, or due the DNA being broken down by an external source, such as radiation. Many viruses are particularly good (or bad, depending on how you look at it!) at making mistakes when they copy themselves, as they don’t have the equivalent of a spell-checker like we do in our cells.

Mutations happen at random. This means they might be good, bad or neither:
~ Bad mutations are generally deleterious – this means that they are bad for the organism in some way (such as a protein for antibiotic resistance no longer working). These organisms are less likely to survive and therefore bad mutations tend to be removed from the population.
~ Good mutations give the organism some sort of advantage – in bacteria, this might be anti-biotic resistance, or in viruses, this might allow them to hide from the immune system a bit longer. These sorts of mutations are more likely to be passed on to the next generation, as they are more likely to survive.
~ Neutral mutations are neither good nor bad. They change the sequence of the DNA, but don’t effect the organism at all.
The balance of these processes over time is known as evolution, and that’s what I’m looking for when I talk about DNA sequences evolving.