1 [ek-son]
(in Britain) one of four yeomen of the guard who act as commanding officers in the absence of higher authority.
Also called exempt.

1645–55; earlier exant, for French exempt (spelling altered to show French pronunciation)

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2 [ek-son]
noun Genetics.
any portion of an interrupted gene that is represented in the RNA product and is translated into protein.
Compare intron.

1975–80; ex(pressed sequence) + -on1

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World English Dictionary
exon1 (ˈɛksɒn)
(Brit) one of the four officers who command the Yeomen of the Guard
[C17: a pronunciation spelling of French exemptexempt]

exon2 (ˈɛksɒn)
Compare intron any segment of a discontinuous gene the segments of which are separated by introns
[C20: from ex-1 + -on]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

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.

ex·on'ic adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
exon   (ěk'sŏn)  Pronunciation Key 
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.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

exon definition

Stretches of DNA in genes that code for proteins. In eukaryotes, exons in a given gene are generally separated from each other by stretches of DNA that do not contain instructions for constructing proteins. (Compare intron.)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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