A non-coding DNA sequence within a gene that is removed during RNA processing. Introns are spliced out before the final messenger RNA is produced.
Coined in 1978 by American molecular biologist Walter Gilbert, combining 'intervening' and 'sequence'. The term was created as the opposite of 'exon' (expressed sequence). It reflects the discovery that genes are not continuous coding sequences but contain interrupting segments.
Introns make up about 95% of some human genes, yet they're completely removed before proteins are made - it's like having a book where 95% of the text is crossed out before reading. Some scientists call them 'junk DNA,' but many introns actually contain regulatory sequences that control gene expression.
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