Ability to mutate is an adaptation

[Dougalbod]

well I don't think DNA repair is ever 100% effective (except for maybe DSB repair which is close to that). Repair pathways miss some stuff, so if you got 100 times as many mutations as normal, it is conceivable that after repairs you are still left with something like 2-3% more mutations as normal, which in turn could increase adaptation

That makes sense but it's not really what I was asking. I was wondering if there is any evidence of adaptations which increase the number of unrepaired mutations when an organism is stressed.

I've just googled this and there is in fact a lot of information so I can answer my own question. The idea I was thinking about is apparently known as 'adaptive mutation'.

http://www.micab.umn.edu/current/adaprev01.pdf

[canalon]

You can also read about what F. Taddei and I. Matic and a few others did about the mutator phenotype in bacteria and its role in adaptation to changing environment.

[CLOVIS]

You are confused on mutations and natural selection. Natural selection is a for or against principle. DNA may or may not have a factor in it. But DNA itself does not need to change to have natural selection. It is critical to understand this. If specimen A has a gene coding for thick fur and specimen B has a gene coding for naked skin, natural selection selects in favor of specimen A. Note that no changes in DNA were made, but just a simple presence of two different genes.

[Dougalbod]

You are confused on mutations and natural selection. Natural selection is a for or against principle. DNA may or may not have a factor in it. But DNA itself does not need to change to have natural selection. It is critical to understand this. If specimen A has a gene coding for thick fur and specimen B has a gene coding for naked skin, natural selection selects in favor of specimen A. Note that no changes in DNA were made, but just a simple presence of two different genes.

Clovis, for the different genes to be present, mutation - changes to the DNA - must have already occurred in the past. Otherwise the two individuals would be genetically identical.

I'm not sure if you are talking about two seperate genes or if you mean different alleles but it doesn't matter, in your example there are either two different alleles of the same gene or two genes with at least one of those two having different alleles.


Dougal

[biohazard]

The singe chromosome of prokaryotes versus multiple chromosomes in many eukaryotes is one way to promote mutations: all mutations that have an effect also express themselves, since there is not "healthy" gene to bypass its effects. If the, for example, needed better protection for mutations, they'd probably have multiple alleles of their genes, but as it stands, the ability of their mutations to instantly have an effect seems to be desirable - it allows much faster reaction times for the species to survie in a changing environment.

Even more (deliberately) mutation prone seem to be many viruses, especially those that lack proof-reading systems or have an RNA genome: in some species there are more unviable particles than viable ones because of the high mutation rate - but it's ok as long as myriads of particles are produced, of which many are perfectly viable, and others have mutations that make them viable if the environment changes (e.g. a new drug is administered or the host immune system learns how to deal with the original virus type)

But if the rate of reproduction is slow (such as is the case with more complex organisms), the rate of mutation cannot be very high - humans as a species, for example, could probably not tolerate a high chance of their offspring having a disadvantageous mutation.

[JackBean]

Why should single chromosome increase the rate of mutations?

[biohazard]

Why should single chromosome increase the rate of mutations?

I didn't say it increases the rate, did I?

I said it promotes mutations, by which I meant that the rate of how often the mutations are expressed is higher and how often they affect the phenotype. Admittedly, my choice of words could have been better :)

If you have one allele of a gene, it's effect always takes place. If you have two, one may dominate over the other. This way many mutations remain recessive and rarely get to affect an individual.

In practical terms: if there is a sudden change in the environment, a bacterial cell that has, say, a mutation that allows it to survive in the precense of a new antibiotic even if the mutation otherwise decreases it's growth rate a bit, survives because other bacteria die. This way a bacterium species can react very quickly to a new environment. You could think of it as a "deliberate" choice to have only one set of genes as it has this kind of advantages.

Humans, on the other hand, would be less likely to react so efficiently to a sudden change in their environment, because it would be much less likely that this protective gene would be present in the both alleles. Two chromosomes of course have their advantages as well - the chance of having viable offspring is better, because one faulty gene is usually not enough to kill your kiddos. It makes sense if you only have one to five offspring during your life time.

For a bacterium that can produce a million offspring in a day it's not that bad if few of them die. More important is that whatever the new environment is going to be, some of them will live.

Thus, I believe, having single genome is an evolutionary way to not increase the number of mutations, but to increase the chance that they have an effect.

[Chroma]

But if the rate of reproduction is slow (such as is the case with more complex organisms), the rate of mutation cannot be very high - humans as a species, for example, could probably not tolerate a high chance of their offspring having a disadvantageous mutation.

I believe I have read that rodents tend to have a higher mutation rate then other mammals. Is anyone able to confirm this? And if so, would that be in relation to rodents having an increased reproduction rate?

Also is there not a environment/species specific ideal mutation rate? Again I'm unsure, but believe I have read that some antiviral drugs work by increasing the mutation rate until the fidelity of genetic information transmission is too low to be effective...