Exon
any part of a gene that will encode a part of the final mature RNA produced by that gene, after introns have been removed by RNA splicing
An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term exon refers to both the DNA sequence within a gene and to the corresponding sequence in RNA transcripts. In RNA splicing, introns are removed and exons are covalently joined to one another as part of generating the mature RNA. Just as the entire set of genes for a species constitutes the genome, the entire set of exons constitutes the exome.
History
The term exon is a shortening of the phrase expressed region and was coined by American biochemist Walter Gilbert in 1978: The notion of the cistron... must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger – which I suggest we call introns (for intragenic regions) – alternating with regions which will be expressed – exons.This definition was originally made for protein-coding transcripts that are spliced before being translated. The term later came to include sequences removed from rRNA and tRNA, and other ncRNA and it also was used later for RNA molecules originating from different parts of the genome that are then ligated by trans-splicing.
Contribution to genomes and size distribution
Although unicellular eukaryotes such as yeast have either no introns or very few, metazoans and especially vertebrate genomes have a large fraction of non-coding DNA. For instance, in the human genome only 1.1% of the genome is spanned by exons, whereas 24% is in introns, with 75% of the genome being intergenic DNA. This can provide a practical advantage in omics-aided health care (such as precision medicine) because it makes commercialized whole exome sequencing a smaller and less expensive challenge than commercialized whole genome sequencing. The large variation in genome size and C-value across life forms has posed an interesting challenge called the C-value enigma.
Across all eukaryotic genes in GenBank, there were (in 2002), on average, 5.48 exons per protein coding gene. The average exon encoded 30-36 amino acids.
This brief starts where responsible research should: with the source description of “Exon” as any part of a gene that will encode a part of the final mature RNA produced by that gene, after introns have been removed by RNA splicing. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the general reference register because the source frames it as any part of a gene that will encode a part of the final mature RNA produced by that gene, after introns have been removed by RNA splicing. Its deeper value depends on whether names, dates, institutions and citations support that framing.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Aug 16, 2026. The linked authority identifier is Q373027. The Library of Congress control number is sh91002875. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank. The first chronological checks are 1978 and 2002.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Exon” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.