A purine or pyrimidine base that differs slightly in structure from the normal bases found in DNA or RNA. Some analogs may be incorporated into nucleic acids in place of the normal base, often resulting in a base substitution mutation. Some examples include aminopurine, azaguanine, azauracil, and 5-bromodeoxyuridine.

A chemical compound that resembles and can replace one of the nitrogenous bases normally found in DNA.

a chemical that can substitute a normal nitrogenous base in nucleic acid s