• Mutations are changes in the sequence of bases in DNA.

• Most mutations occur for no known reason.

• Many mutations don't seem to matter, but some do.

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Remember, every cell in your body contains copies of the same DNA molecules. Ideally, each copy should be absolutely identical. But, with so many copies being made, it is hardly surprising that changes - mutations - sometimes creep in. These mutations occur at random.

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Remember, most (98%) DNA is not in genes. Since mutations strike at random, chances are most will miss all the genes. If so, they probably won’t matter. All of us have lots of mutations that we don’t know we have.

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Even if a mutation does strike a gene, then it still might not matter much. For example:

• Not all mutations prevent the gene making a protein that works. It depends exactly what the mutation is.

• Cells sometimes compensate for mutations in some way and to some extent.

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But … IF a mutation stops a gene from making its protein properly, IF compensation can’t occur, and IF this happens in the early embryo and the mutation is copied into many cells, then the child might grow up different in some ways from most other children.

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Hopefully, you can see why this scenario is rare. It can be difficult to diagnose, mutations in different parts of the gene are liable to have different effects and it’s complicated to work out why a particular mutation has had the effects that it has.