What is a genetic mutation?

A mutation is a random change in the amount of DNA or sequence of DNA nucleotides within a cell. DNA is a double helix with two polynucleotide strands joined by hydrogen bonds between complementary base pairs. This structure is usually very stable, but mutations can randomly occur during DNA replication and also in the presence of mutagens (e.g. ionising radiation). Genetic mutations involve insertions, deletions, substitutions, inversions, changes in the number of repeat units, deamination (e.g. cytosine can be deaminated to form uracil) or depurination (resulting in the conversion of a nucleotide into a sugar-phosphate residue).