What is meant by 'random' in DNA mutation?

  • Thread starter Graeme M
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  • #26
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Whatever the cause of a mutation may be, what it means physically is that the sequences of bases in some part of the DNA gets altered.
There are a number of known reasons why this can happen, viruses being one example, and EM radiation being another.
Most of the time such a mutation results in a non functional or possibly harmful protein being produced instead of what was originally encoded.
Occasionally though, the new encoding 'luckily' produced an improvement instead.
 
  • #27
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I understand the redundancy being necessary for correction of random imperfections. But what if the mutation can no longer be corrected but replicates as per instruction of the mutated DNA.
Neutral mutations are not visible to selection, so they are not "corrected" but propagated.* Hence it is possible that a following base pair change may be more severe than if the first didn't happen. (Change to a different amino acid.)

[*Something similar happens for so called "near neutral mutations" in real life populations. Population genetics can show that you need ever larger populations and time to pick up variations with ever smaller effects and either promote or eliminate them. But I mention this to be complete, it isn't necessary to know about it for understanding variation as such.]

I think "correction" is the wrong term here. First because variation is inherently neither bad nor good, it is simply necessary for evolution, which is what makes populations survive a range of sufficiently large environmental change to lead to extinction else.** Second because there are DNA repair mechanisms for broken strands and what not, so I would use "repair" in that case.

[** And to be complete again, some changes are too large or too rapid to be mooted that way. I am just learning more about the Great Dying, the end-Permian extinction, where 90 % of all organisms disappeared. I wasn't troubled before, because life has survived so many mass extinctions. (And the previous Great Oxygenation Event was probably an even larger killer, but we can't see that yet.)

But it took unusually long before the wound healed, 10+ million years for ecological balance and _100+_ million years for recovery of diversity. (When most mass extinctions are recovered on both counts after 1-10 million years or so.) And the species that survived seemed to have been precisely random outcomes! No discernible patterns of "better" robustness. (Compare with the KPg extinction that hit herbivorous and carnivorous dinosaurs, while insectivorous mammals and perhaps insectivorous avian dinosaurs survived, so a distinct pattern.)

It appears a diversified biosphere helps but is not the ultimate answer to all change. And of course when our star eventually starts to die, so does life... But now I appreciate the limits of evolution more.]
 
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