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exon ex·on (ěk'sŏn)
A nucleotide sequence in DNA that carries the code for the final mRNA molecule and thus defines a protein's amino acid sequence. Also called coding sequence.
A segment of a gene that contains information used in coding for protein synthesis. Genetic information within genes is discontinuous, split among the exons that encode for messenger RNA and absent from the DNA sequences in between, which are called introns. Genetic splicing, catalyzed by enzymes, results in the final version of messenger RNA, which contains only genetic information from the exons. Compare intron.