What does exon mean?
An exon is a segment of a gene that survives the editing process of RNA splicing and contributes to the final functional product, usually a protein. Genes in complex organisms are built from alternating blocks: exons, which carry coding information, and introns, which are cut out before the RNA is translated. Because a single gene's exons can be assembled in different combinations — a process called alternative splicing — exons allow one gene to yield many distinct proteins. The term was coined by molecular biologists in the late 1970s, drawing on the Greek prefix exo-, meaning 'outside', to signal what remains outside the excised portions of the transcript. Today 'exon' is central vocabulary in genomics: techniques such as whole-exome sequencing target exons specifically because most disease-causing mutations cluster there. It is precise scientific terminology, appearing mainly in research literature, clinical genetics, and science reporting rather than everyday conversation.
nounA segment of a gene that codes for a portion of a protein or mature RNA product and is retained after splicing; exons are separated by non-coding regions called introns.
- A segment of a gene that is represented in mature messenger RNA and typically encodes part of a protein; exons remain after introns are spliced out.
"The mutation was located within the third exon of the gene, disrupting protein production entirely."
"Researchers found that a single base change in one exon could cause the entire disorder."
"Alternative splicing allows a single gene's exons to be rearranged into many different proteins."
Standard regular plural; used freely in technical contexts.
"Human genes typically contain multiple exons separated by much longer introns."
Your DNA is mostly filler — exons are the precious few percent that actually spell out proteins, and they were only named in the late 1970s.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of exon
The word 'exon' was coined in the late 1970s by American molecular biologist Walter Gilbert, following his work on the discovery of split genes. It derives from the Greek prefix exo- ('outside') combined with the suffix -on, echoing terms like 'cistron' and 'codon' in genetics. Gilbert introduced it as the counterpart to 'intron', which he also coined, distinguishing the expressed regions of a gene from those removed in RNA processing.
Related word forms
How exon is actually used
Strictly technical vocabulary used in molecular biology, genetics, and medicine. The term is essentially never encountered in casual speech, though it appears increasingly often in journalism covering gene therapy and genomic medicine.
Easily confused with exon
An intron is the opposite of an exon: a non-coding segment of DNA that is removed during RNA splicing rather than retained.
An axon is the long fibre that transmits nerve impulses in a neuron, whereas an exon is a coding segment of a gene.
To exonerate means to clear someone of blame or guilt, while an exon is a unit of genetic code; they share only Greek roots meaning 'out of'.