noun, plural: introns
(molecular biology) A noncoding, intervening sequence of DNA within a gene that is transcribed into mRNA but is removed from the primary gene transcript and rapidly degraded during maturation of the RNA product
An intron is a nucleotide sequence within a gene. It is a noncoding sequence. During the final maturation of the RNA product, the RNA removes it by splicing.1 The term intron pertains to the DNA sequence within a gene as well as the corresponding sequence in the RNA transcripts.2 It is used in contrast to the nucleotide sequences joined together in a mature RNA after splicing called exons. Sometimes, the term intron is used synonymously to intervening sequences. However, the latter is a broader term that includes inteins and UTRs, apart from the introns.
Introns occur in the genes of many organisms (e.g. eukaryotes), including viruses. They are also present in the genes of mitochondria and chloroplasts. Introns are believed to be essential in allowing rapid evolution of proteins through exon shuffling.
1 Alberts, B. (2008). Molecular biology of the cell. New York: Garland Science.
2 Kinniburgh, Alan; mertz, j. and Ross, J. (July 1978)."The precursor of mouse β-globin messenger RNA contains two intervening RNA sequences". Cell 14 (3): 681–693.