Most of a person’s inherited characteristics are due to the sequences of units within the genes making up their DNA, these changing from one generation to the next. Epigenetic influences refer to additional changes in genes which are not due to changes in the DNA sequence, but involve the addition or removal of small molecules to the outside of the gene. These may determine whether the gene is ‘switched on’ or ‘switched off’, thus affecting whether a characteristic coded by the gene is expressed or not.