4
$\begingroup$

Principle of genetics mentions

The fact that introns accumulate new mutations much more rapidly than exons indicates that many of the specific nucleotide-pair sequences of introns,excluding the ends, are not very important.

Though 'are not very important' is not true as introns do have a number of functions (both discovered and undiscovered).

But why is DNA polymerase less efficient at replicating introns? Is it known?

$\endgroup$
  • 3
    $\begingroup$ Note it doesn't say polymerase is less efficient; rather that mutations accumulate. This could be because of things other than different rates of new mutation creation. $\endgroup$ – mgkrebbs Dec 26 '16 at 17:39
  • 6
    $\begingroup$ Some introns might contain functional parts is very different from all introns are functional. The web site you linked is no proof. Indeed, it seems to be written by someone supporting the intelligent design hypothesis for the human genome (which of course, IMO, is wrong). So it is an opinion-based site containing also some information about biological facts. I would stick to more neutral references including standard Biology books. $\endgroup$ – ddiez Dec 27 '16 at 3:02
  • 1
    $\begingroup$ "Accumulates" is the key term, the mutation rate is not higher, mutations are just less likely to be removed, which makes sense if the area is non-functional, most of the mutation will have no effect thus are unaffected by selection. $\endgroup$ – John Aug 21 '18 at 1:55
  • $\begingroup$ Is there any evidence that the mutation rate is higher in introns than exons? Isn't it the fixation rate that is higher in introns than in exons? $\endgroup$ – Remi.b Jan 31 at 14:53
8
$\begingroup$

Not less efficient, but introns are under less selective pressure than exons. Exons actually encode the protein. A single bp insertion will ruin a mRNA encoding a protein by causing a frame shift in how the sequence is read.

However the same is not true for introns. 1bp insertion even if the intron has function such as transcription or translation factor regulation has a higher chance of not damaging anything important. Simply because such factors are spaced apart and the space is not really important.

http://www.nature.com/scitable/topicpage/rna-splicing-introns-exons-and-spliceosome-12375 https://www.ncbi.nlm.nih.gov/pubmed/17570818

$\endgroup$
  • 2
    $\begingroup$ This is not completely true. Insertions in introns also cause frame shifts which may render splice acceptor sites non-functional. This also affects the protein coding sequence. $\endgroup$ – Chris Dec 26 '16 at 8:19
  • 3
    $\begingroup$ Only the very terminal ends of an intron are involve in splicing and the branch point can tolerate fair amount of change as long as the 'A' branching point is unchanged. So only a few bp of an intron in constrain by splicing requirements. And given that mammalian intron are large, most of the intron is just space. $\endgroup$ – JayCkat Dec 26 '16 at 8:45
  • 3
    $\begingroup$ @JayCkat It would be great if you can add some references. $\endgroup$ – WYSIWYG Dec 26 '16 at 9:53
  • $\begingroup$ @JayCkat It is OP's job to clarify the question but is there any evidence that the mutation rate is higher in introns than exons? Your answer seem to rather tackle the question "why is fixation rate higher in introns than in exons?" and not "why is mutation rate higher in introns than in exons?" $\endgroup$ – Remi.b Jan 31 at 14:53
  • $\begingroup$ If you ask the question "Do intron have a higher replication error than exons during DNA replication", the answer is maybe. Longer answer is DNA polymerase have difficulty accurately replicating nucleotide repeats (mono, di, tri). Such repeats are more likely to appear in Introns compared to exons. These repeats do expend and shrink during DNA replication, independent of homologous recombination. However accurate sequencing of such repeats is difficult, so in vivo occurrence is next to impossible to verify. Only real solution is to wait for minion seq tech to mature. $\endgroup$ – JayCkat Feb 2 at 3:20
5
$\begingroup$

One paper after this question was asked indicates that it might be both stronger purifying selection in exons and a higher basal mutation rate in introns, likely due to the different accessibility of the DNA.

You are correct that introns play an important role in regulation (perhaps both timing and overall expression, in addition to the presence of enhancers and the potential for alternative splicing that affect the actual protein produced).

$\endgroup$
  • $\begingroup$ It is OP's job to clarify the question but is there any evidence that the mutation rate is higher in introns than exons? Your answer seem to rather tackle the question "why is fixation rate higher in introns than in exons?" and not "why is mutation rate higher in introns than in exons?" $\endgroup$ – Remi.b Jan 31 at 14:54
  • $\begingroup$ Please see the first linked paper (someone else chose the link location, and maybe I should change this). The other answer addresses fixation rate and it's well established so I didn't link anything about that. Perhaps you meant to add this comment to that thread? $\endgroup$ – GenesRus Feb 1 at 0:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.