Components of DNA or RNA. In DNA there are four chemical bases: adenine (A), guanine (G), thymine (T) and cytosine (C). In RNA the bases are identical except for thymine which is replaced with uracil (U).
Use in clinical context
The order of bases in a gene determines the order of amino acids in a protein. Changes to the bases can result in changes to the amino acids and the resulting protein function. This can result in changes to the individual, such as differences in hair or eye colour, or the development of health conditions.