Cistron

Part of speech: noun

Definitions

1. A segment of deoxyribonucleic acid that codes for a single functional polypeptide chain or ribonucleic acid molecule
2. A section of DNA that encodes the information necessary for producing a specific protein or RNA molecule
3. A unit of genetic material within DNA that specifies the instructions for synthesizing a particular protein or RNA molecule

Etymology: Seymour Benzer, an American molecular biologist, coined "cistron" in 1957 while studying the fine structure of genes in bacteriophage. He needed a way to test whether two mutations that looked alike actually damaged the same unit of heredity, and he used a "cis-trans comparison" for this purpose. Mutants placed on the same chromosome (cis) and on opposite chromosomes (trans) could be compared, and the results indicated whether the defects lay in one functional unit or two. The name is a blend of "cis" and "trans," the Latin prepositions meaning "on this side" and "across," with the suffix "-on," which was conventionally used in the 1950s for units of matter and of biological structure, such as "electron" and "codon"-era terms. Benzer's name thus encodes the experimental test that defined the unit: the gene was identified not by its chemistry but by the genetic logic of that comparison.