A segment of DNA that codes for proteins and is expressed in the final RNA product after splicing.
Coined in 1978 by American biochemist Walter Gilbert from 'expressed sequence', contrasted with 'intron' (intervening sequence). The term reflects the gene's expressed, coding portions.
Humans have about 180,000 exons across all our genes, but they make up only about 1% of our total DNA. The discovery of exon shuffling helped explain how evolution creates new proteins by recombining existing functional domains.
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