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Author Topic:   Will mutations become less freqent?
Elliot
Inactive Member


Message 1 of 25 (332243)
07-16-2006 4:41 PM


After some thought, I was wondering if genetic mutations will be less frequent.
DNA is transcribed and transcripted via several enzymes (including DNA replicase, helicase etc), and this is when the mutations occur. Well what if there was a mutation in the DNA, and one or more of those enzymes were more accurate when copying or transcribing DNA - there would be less random mutations. This new DNA would be more favourable, as long as the environment was stable and devoid of major changes, as it would be copied more accurately compared to other DNA strands in other animals.
This would continue, and the enzymes becoming more accurate (other factors other than enzymes can be considered, e.g. the solution in the nuclear envelope, but I'll just stick to enzymes) until the probability of mutation is incredibly small.
This also offers a small explaination to the dinosaurs, because if they had less DNA mutations then they would be less likely to survive a major climate change.

Replies to this message:
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AdminNosy
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From: Vancouver, BC, Canada
Joined: 11-11-2003


Message 2 of 25 (332272)
07-16-2006 6:20 PM


Thread moved here from the Proposed New Topics forum.

  
crashfrog
Member (Idle past 1467 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 3 of 25 (332344)
07-16-2006 9:00 PM
Reply to: Message 1 by Elliot
07-16-2006 4:41 PM


This would continue, and the enzymes becoming more accurate (other factors other than enzymes can be considered, e.g. the solution in the nuclear envelope, but I'll just stick to enzymes) until the probability of mutation is incredibly small.
This also offers a small explaination to the dinosaurs, because if they had less DNA mutations then they would be less likely to survive a major climate change.
Then it sort of reaches an equilibrium, then, doesn't it? Where members of a species become so homologous and clonal that a single disease or something wipes them all out - except for the mutants in the population who didn't inherit the "perfect" polymerase sequences, etc.

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sfs
Member (Idle past 2533 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 4 of 25 (332369)
07-16-2006 9:40 PM
Reply to: Message 3 by crashfrog
07-16-2006 9:00 PM


quote:
Then it sort of reaches an equilibrium, then, doesn't it? Where members of a species become so homologous and clonal that a single disease or something wipes them all out - except for the mutants in the population who didn't inherit the "perfect" polymerase sequences, etc.
Right. The more variable the environment, the more useful a higher mutation rate will be. Also, making DNA replication more faithful (and making transcription and recombination less mutagenic, etc) probably carries a direct cost to the organism, either in the time required for replication or the energy requirements. So a balance is likely to be achieved, not an endless improvement. Start searching on "evolution of mutation rates" and see what you find.

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 5 of 25 (332438)
07-17-2006 2:39 AM
Reply to: Message 1 by Elliot
07-16-2006 4:41 PM


My understanding is that the mutation rate has evolved (see Darwin in the Genome by Lynn Caporale).
I beleive that Caporals is correct. As the mutation rate decreases, so does the fitness advantage of further "improvements" in copying fidelity. At some point we hit the situation where the mutatiion spreads so slowly that environmental changes will arrive before it becomes fixed in the population.
It isn't a plausible explanation for the dinosaur extinction because that would require many different species to suffer the same effect, independantly.r

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 Message 1 by Elliot, posted 07-16-2006 4:41 PM Elliot has replied

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 Message 6 by Elliot, posted 07-19-2006 11:56 AM PaulK has replied

  
Elliot
Inactive Member


Message 6 of 25 (333289)
07-19-2006 11:56 AM
Reply to: Message 5 by PaulK
07-17-2006 2:39 AM


I was still theorising in a stable environment, which is entirely possible. If the environment was changing then this new DNA would be wiped out very quickly.
Also have you never heard of convergent evolution? If the dinosaurs had a steady environment then they would have less need for mutations.

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 Message 10 by RAZD, posted 07-21-2006 10:06 PM Elliot has replied

  
PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 7 of 25 (333298)
07-19-2006 12:04 PM
Reply to: Message 6 by Elliot
07-19-2006 11:56 AM


I have heard of convergent evolution. And the idea that all the dinosaurian species (except birds) not to mention the marine reptiles (e.g. icthyosaurs and plesiosaurs) would all converge in that way is not plausible. You really need to consier the diversity of the dinosaurs and other victims of the K/T mass extinction before you make speculations on the cause.

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Elliot
Inactive Member


Message 8 of 25 (333311)
07-19-2006 12:18 PM
Reply to: Message 7 by PaulK
07-19-2006 12:04 PM


Well the stability of the environment would differ depending on the habitat of the species. So land and sea animals may have got the worst of the meteor (if there was one).
The age of the species and the stability of the environment will also determine how accurate their DNA transcription and translation is.
Also referring to the weak anthropic principal (best argument of them all ), the reason we only see the bird and mammals, and no dinosaurs (yet lol) nowadays is because they were the only ones to survive.

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Scaryfish
Junior Member (Idle past 6291 days)
Posts: 30
From: New Zealand
Joined: 12-06-2004


Message 9 of 25 (333870)
07-20-2006 11:10 PM
Reply to: Message 1 by Elliot
07-16-2006 4:41 PM


As others have said, there are three things that will affect mutation frequency:
1) diminishing returns for further fidelity
2) metabolic cost of increased fidelity
3) the benefit of having some mutation. This is kind of counter-intuitive, as most mutations are harmful or neutral, but (at least in bacteria) an increased mutation rate, particularly in stressful environments, can be a benefit. Some bacteria will increase their own mutation rate in response to stresses such as antibiotics or starvation. This is thought to provide a benefit - basically if you're going to die because of the stressful environment, then the risk of deleterious mutations is outweighed by the possible beneficial mutations. Provided you can pull the mutation rate back down when required.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 10 of 25 (334141)
07-21-2006 10:06 PM
Reply to: Message 6 by Elliot
07-19-2006 11:56 AM


I was still theorising in a stable environment, which is entirely possible.
You would need to eliminate seasons, all climate variations, all tecktonic effects and all predator-prey relationships.
Also have you never heard of convergent evolution? If the dinosaurs had a steady environment then they would have less need for mutations.
I'm not sure you understand convergent evolution or you are not conveying what you are meaning here. It has nothing to do with the rate of mutation, and the organisms would still need to evolve to converge.
Are you thinking that all life would end up as essentially one (1) type of plant (all plants converged), one (1) type of herbivore (all herbivores and some omnivores converged) and one (1) type of carnivore (all carnivores and remaining omnivores converged)?
Even with that scenario you would have the ongoing "arms-race" between the eaten (to not be eaten) and the eater (to eat).
Welcome to the fray.
Enjoy.

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This message is a reply to:
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Elliot
Inactive Member


Message 11 of 25 (334203)
07-22-2006 4:40 AM
Reply to: Message 10 by RAZD
07-21-2006 10:06 PM


I am talking about convergent evolution that some (or all) species could evolve more accurate condititions for DNA replication and transcription. (Not into one species )
When I mean stable, I don't mean rapidly changine. You can still have animals that don't evolve, yet cope well with seasons, it's not like their DNA spontaneously mutates when it comes to winter.
Climate variations in some areas are stable (e.g. islands where the water around stabilises the temperature.
Techtonic effects don't happen everywhere, some land masses don't even lie on any techtonic boundary. And the predator-prey relation ship maintains itself generally, if you look at graphs mapping time against number of animals, the predator and prey line fluctuate, with the predator line being slightly after.
Overall I am saying that in an environment which is not rapidly changing, species would evolve more accurate means of copying DNA. This would then propagate around the DNA pool, as there would be more copys of it and less mutation when copying. Think of this as "I it works, don't fix it", as if the animal is doing well and there is little need to change, it is guarding against bad mutations (such as sickle cell aenema and other ,especially resessive, genetic diseases) which could theaten the population.
Also remember that you do have variation in the population, and natural selection would continue evolution.
If the environment was changing, then this would be a disadvantage, having lower mutations, as there would be a lower probability that an animal will have a unique adaptation allowing it to survive and propagate that gene.

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Modulous
Member
Posts: 7801
From: Manchester, UK
Joined: 05-01-2005


Message 12 of 25 (334213)
07-22-2006 7:37 AM
Reply to: Message 11 by Elliot
07-22-2006 4:40 AM


Overall I am saying that in an environment which is not rapidly changing, species would evolve more accurate means of copying DNA
Possibly. However, this makes the assumption that the current fidelity system can be improved without first getting worse or incurring some other penalty on the individuals that inherits it. I don't know if this is the case.
I suppose another condition that might be necessary is that the species is highly specialized and most/any mutations would be negative.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 13 of 25 (334261)
07-22-2006 11:13 AM
Reply to: Message 11 by Elliot
07-22-2006 4:40 AM


Other solutions
Overall I am saying that in an environment which is not rapidly changing, species would evolve more accurate means of copying DNA
I don't see that this is likely. It sounds like you are suggesting selection at the population level.
The only way this could be selected for is if having fewer mutations increased the rate of live births. It seems to me that other solutions exist for this so the lower mutation rate may not be encountered and selected for over those.
As was suggested above, if almost all mutations are harmful (because a population is very well adapted to an unchanging environment) then the usual natural selection would remove them. The reduced mutation rate would have to, somehow, result in greater fecundity. That may be possible but might not be reached.

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Elliot
Inactive Member


Message 14 of 25 (334268)
07-22-2006 11:43 AM


Stable environment do exist.
Take some fossils for example, some species which we have fossils for that still exist, their skeletal structure remains similar, these are millions of years apart, and as they have little need to change, they don't.
And if their current form is working just fine, then the risk of a bad mutation would outweigh the benefits of a good one, so the DNA process (rightly said - IF it can be improved) would be more accurate.
The birth rate would not need to increase, a species does NOT have to evolve further, chances are it will, but it does not have to.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 15 of 25 (334469)
07-23-2006 8:33 AM
Reply to: Message 14 by Elliot
07-22-2006 11:43 AM


Stable environment do exist.
I disagreed, and have posted why. You chose to minimize the effects, but by doing this you are ignoring the need for variations involved.
At best there are environments that oscillate around a median, but even then those oscillations cause adaptations and variations to be selected. These may be no more significant than the change in beak size of the Galapagos Finches studied by Grant and Grant
Just a moment...
But these are still changes and they are still selection responses to variations in the environment. They still have the repository of accumulated genetic {genome} plus new beneficial (to current "micro?" environment) and the accumulation of {previously neutral} mutations that may or may not be beneficial in the changes-- those that are get selected for (larger beaks in dry periods, small beaks in wet periods) those that aren't get de-selected (small beaks in dry periods, large beaks in wet periods). The population on a whole appears unchanged, but they have oscillated between different forms -- forms that were available due to the level of mutations the population had in reserve due to mutations.
If the DNA had selected for such a low level of mutation that {large\small} beaks would not exist in the population the species would have become extinct even though the environment was "stable" ... (by your definition when you excluded the variations I mentioned).
Take an example of two people with bank accounts, they each earn $100 a week and spend $100 a week, they both have their earning automatically deposited in a bank account and use debit cards to spend with. One has no buffer, the account is empty just before the next deposit, and the other has $1000 in buffer: which will be able to survive economic oscillations in their costs that force them to exceed spending $100 in one week?
Take some fossils for example, some species which we have fossils for that still exist, their skeletal structure remains similar, these are millions of years apart, and as they have little need to change, they don't.
The fact that we have species alive today that are related to ancient species does not mean they are unchanged.
Crocodiles
Sharks
Coelacanths
and the like
Are all different species today than the ones alive millions of years ago. Size and other morphological changes have occurred as well as divergence from those ancient forms.
Further, their ancestors survived (1) ice ages and (2) the K-T extinction event caused by the Yucatan meteor strike 65 million years ago (as have the ancestors of all life today) -- so they can not be said to have lived in stable environments.
And if their current form is working just fine, then the risk of a bad mutation would outweigh the benefits of a good one, so the DNA process (rightly said - IF it can be improved) would be more accurate.
There is a logical error here. As pointed out, most mutations are harmful, and they are handled by the current selection just fine. If the current method of dealing with bad mutations is working just fine, then the risk of bad mutation to the species as a whole is virtually non-existent.
It is not harmful mutations that cause extinction, rather it is lack of adaptation that causes extinction, and every time selection is for a slight adaptation to best fit the current environment, then there is selection for sufficient mutations to provide the diversity.
The logical conclusion is that if the rate of mutation has evolved (or rather the susceptibility to mutation) that then this occurred a long time ago, long before dinosaurs evolved, before the P-T extinction event.
There does seem to be evidence that some sections of DNA are more susceptible to mutations than other, and there is evidence that bacteria can change their rates of mutation, increasing it when they are environmentally stressed, and both of these lines of evidence would indicate that the minimum level of mutation needed for the ongoing survival of life in general (not just of species) has evolved ... and already reached an equilibrium with the need for variations.
Enjoy.

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we are limited in our ability to understand
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This message is a reply to:
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