Why are introns called 'introns' when they are the actual ones who are getting spliced out from the pre-mRNA. Shouldn't exons be named introns as they are the ones that are 'in' and are not 'exiting'? On what criteria were they named like this?

  • $\begingroup$ It confuses me too. Shrug. $\endgroup$ – Joshua Feb 4 '18 at 21:37
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    $\begingroup$ Introns stay inside the nucleus, exons exit the nucleus. $\endgroup$ – user40046 Feb 5 '18 at 0:53
  • $\begingroup$ It’s not actually true that introns always stay inside the nucleus. There is a lot of research discussing the role of extranuclear introns playing a role in translation regulation. $\endgroup$ – canadianer Feb 6 '18 at 22:28
  • $\begingroup$ I'm amazed how many votes this has got. Shows that there is a general confusion among those new to the topic. If I were still teaching this, I'd make an extra effort to clarify the origin of the expression. I withdraw my close vote. $\endgroup$ – David Feb 6 '18 at 22:50
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    $\begingroup$ @David It was in the "Hot Questions" list, which makes it visible to everyone across Stack Exchange. $\endgroup$ – canadianer Feb 6 '18 at 23:19

The terms intron and exon were coined by Walter Gilbert in a renowned 'News and Views' article, Why Genes in Pieces, published in the journal Nature in 1978.

Introns are the intragenic regions and exons are the regions which are expressed.

This is the relevant passage in full:

The notion of the cistron, the genetic unit of function that one thought corresponded to a polypeptide chain, now must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger - which I suggest we call introns (for intragenic regions) - alternating with regions which will be expressed - exons. The gene is a mosaic: expressed sequences held in a matrix of silent DNA, an intronic matrix.

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  • $\begingroup$ Yeah I got the link of the article from Nature.com . Thanks $\endgroup$ – Jewel Johnson Feb 4 '18 at 13:02

Well, as this question seems to be about helping the X- or M- generations get to grips with baby boomer terminology, let me explain how I remember what introns are.

Before Gilbert coined the term (as @xusr explains) original reports of the research that established the mosaic nature of eukaryotic genes refered to

in-tervening sequences.

For example, there was a paper from Phil Leder’s lab in 1978 entitled

Intervening sequence of DNA identified in the structural portion of amouse β-globin gene

So intron was really related to intervening in its origin, and knowning this it is easy to remember which is which — introns and exons.

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