Biology-Online • View topic - Probability of a given mutation

## Probability of a given mutation

Discussion of everything related to the Theory of Evolution.

Moderator: BioTeam

### Probability of a given mutation

Hello everyone,

I'm new on this board, and this is the first question I want to ask here. Darwin's theory is widely known as a framework in which random mutations allow adaptation to the environment through natural selection. But in my view, an important question is : has a given mutation the same probability to occur in different environments? Or does the environment modify the probability law mutations obey? If so, would you have any reference of works related to such an issue?
Yokodachi
Garter

Posts: 1
Joined: Thu Mar 03, 2011 6:15 pm

### Re: Probability of a given mutation

Hi and welcome.

The answer is infintely variable. Each potential mutation has a differing probability of occurring, and that probability varies according to the chemistry the cell experiences (such as toxins ingested) and according to the amount and type of radiation experienced.

Assuming these factors do not change from one environment to the next, the probability of a specific mutation occurring should not change either.

One thing worth remembering, though, is that most mutations are rather trivial, and have little impact on the organism with that mutation. This means that the mutation will not be selcted for or against. Instead, these mutations remain in the gene pool. Over time, sheer chance may make them increase or decrease in frequency. The point is that, if the environment changes, mutations are already present, and if the old mutation now is advantageous in the new environment, it will rapidly increase in gene frequency due to natural selection. New mutations may not be needed for a genetic change to occur.
skeptic
Coral

Posts: 119
Joined: Tue Apr 14, 2009 2:44 am
Location: New Zealand

### Re: Probability of a given mutation

DNA is not a long straight chain, it twists and turns, depending on the sequence of base pairs (codons), and as a result, some areas of the DNA are more prone to mutation than others. That means that if there are a number of different ways of encoding the same thing, some will be more prone to mutation than others.

I remember reading something about there being four bases in the DNA, but two of them serve the same purpose as far as protein encoding is concerned, so that its really a 3-letter code. The interesting thing was, the probability of mutation changed, depending upon which of the two codons was used. The two different codons gave different DNA geometries, which gave different mutation probabilities.

There is also the possibility that the particular order in which proteins are encoded on the DNA doesn't matter, as far as protein production is concerned. However changing the order in which they are encoded on the DNA will affect the geometry of the DNA, which will alter mutation probabilities.

I'm quite sure that this would lead to the least mutative geometry being used when the protein must not mutate without disastrous results, but if the protein must remain flexible in order to adapt to potentially changing environment, then a more mutative geometry would be used.
Rap

Posts: 60
Joined: Tue Jan 18, 2011 5:57 pm

you remember something about four bases in the DNA but two have the same purpose and thus there is 3-letter code? You should definitely study much more!
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

JackBean
Inland Taipan

Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm

### Re:

JackBean wrote:you remember something about four bases in the DNA but two have the same purpose and thus there is 3-letter code? You should definitely study much more!

Hey, JackBean, help us out here, then, ok?
Rap

Posts: 60
Joined: Tue Jan 18, 2011 5:57 pm

the codons are 3-letters, because we have 20 amino acids (+ STOP), so 2-letter code wouldn't be enough.
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

JackBean
Inland Taipan

Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm