Dr Robin Cotton discusses how mutations occur in DNA

Student:
How do mutations occur?

Robin:
Well, they occur by chance and they occur um, each of us came from one sperm and one egg and in the formation of those sperm and eggs you can have an occasional mutation, an occasional difference, and in fact all those mutations are what cause the differences that we test for.

Some mutations are good, some mutations it doesn't matter that they're there, and some mutations are bad.

And so, over evolutionary time the bad mutations get weeded out and the good ones stay but mutations can also be caused by chemicals and by ultraviolet light.