1. (DNA) A fragment of known size used as reference for analytical purposes.
  2. (genetic) A gene with known phenotype and mapped position.
  3. (chromatography) A reference substance co-chromatographed with the sample to assist in identifying the components.
PAC, 1992, 64, 143 (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 159
PAC, 1993, 65, 819 (Nomenclature for chromatography (IUPAC Recommendations 1993)) on page 837
Orange Book, p. 97