marker

https://dx.doi.org/10.1351/goldbook.M03705
  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.
Source:
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