What does cistron mean?
A cistron is the fundamental functional unit of heredity: a stretch of DNA whose nucleotide sequence carries the instructions for building one polypeptide chain or one functional RNA molecule. The term was introduced by the American geneticist Seymour Benzer in the mid-1950s to describe the units revealed by his elegant cis-trans complementation test, which could distinguish whether two mutations lay in the same functional unit or in different ones. In everyday scientific usage, a cistron corresponds closely to what we now simply call a gene, and because of this overlap the word has gradually fallen out of favour, surviving mainly in genetics courses, classical papers, and discussions of prokaryotic operons, where single transcripts may contain several cistrons. Understanding the cistron remains valuable because it captures a key conceptual shift in twentieth-century biology: the recognition that heredity is organised into discrete, linearly arranged units of function along the chromosome.
nounA cistron is the smallest functional unit of heredity — a segment of DNA that codes for a single polypeptide chain or functional RNA molecule; in modern terms it is essentially equivalent to a gene.
- A segment of DNA that encodes a single polypeptide chain or functional RNA molecule, considered as the basic functional unit of heredity.
"The mutation mapped to the same cistron on the bacterial chromosome."
"Each cistron in the operon produces a distinct enzyme required for lactose metabolism."
"Benzer's fine-structure mapping showed that recombination could occur even between mutations within the same cistron."
Standard English plural; commonly used when discussing multiple coding units within an operon or genome.
"The long transcript contains several cistrons translated in sequence."
'Cistron' was coined by geneticist Seymour Benzer from his famous cis-trans test — a word born literally from a lab experiment's name.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cistron
The term 'cistron' was coined in the mid-1950s by the American geneticist Seymour Benzer, who derived it from the 'cis' and 'trans' configurations used in his complementation test for distinguishing functional units of DNA. The element 'cis-' ultimately comes from the Latin adverb cis, meaning 'on this side', the same root behind words like cisalpine. Although widely used in genetics literature through the 1960s, it was progressively displaced by the simpler and broader term 'gene'.
Related word forms
How cistron is actually used
A technical, formal term used mainly in genetics and molecular biology textbooks and older literature. Since the 1960s it has largely been replaced by 'gene' in general usage, though it persists where precision about a single-protein coding unit matters, especially in discussions of prokaryotic operons and polycistronic transcripts.
Easily confused with cistron
An exon is any protein-coding segment within a eukaryotic gene that survives splicing, whereas a cistron is defined by function as a unit producing one polypeptide or RNA product.
A codon is a triplet of nucleotides specifying one amino acid, while a cistron is the entire stretch of DNA containing many codons needed to build one complete polypeptide.
A gene is the broader modern term for a hereditary unit, while 'cistron' is an older, more precise term for the portion of DNA encoding a single polypeptide or functional RNA.