Mutation and its role in evolution: A beginners guide

I appreciate that those sections were a bit arcane, my only defense is that I was responding directly to Jazzns questions about non-genetic mutations rather than trying to frame something in simpler terms as in the OP.Sometimes it is hard to explain a concept without first providing considerable background information, and if I did that in any depth for epigenetics it could take up pretty much a whole thread on its own.I think that a lot of discussion of epigenetics and other more abstruse topics is only likely to derail this thread. I was really hoping to focus more on straightforward genetic mutation since that is the most exstensively studied.TTFN,WK

I'm not sure how valuable a list of all known causes of mutation would really be to this discussion. As far as the more specific questions go common environmental factors and common properties inherent in the processes of DNA replication and repair are common sources of mutation. Excessive mutational loads due to abnormal envionmental states, such as very intense radiation exposure or exposure to high levels of chemical mutagens, are far more likely to produce large scale damage to DNA leading to health problems, such as cancer or sterility or death in the case of very high levels of radiation.The major source of background radiation exposure is atmospheric radon and in terms of the cell the largest source is radioactive ⁴⁰K, there is research showing that that this ⁴⁰K does not significantly vontributr to the rate of spontaneous mutation (Gevertz et al., 1985).The university of Kansas has a page from some lecturer's notes detailing various sources of mutation, here.TTFN,WK

Thanks for clearing that up. I think I understand it now. So really then we can just talk about genetic mutation since the source of the enzymes are genetic. Even in a round about way these mutations are genetic, just second hand.

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

No. That isn't right. As Aegist pointed out you don't need methyltransferases to get methylation of DNA, they are just the enzymes that actively methylate or demethylate the DNA in the cell as a normal part of development. In many cases it is epigenetic modification of DNA which leads to the specific patterns of gene expression characteristic of a particular cellular lineage.You might as well say that it is basically genetic because there has to be DNA to methylate in the first place.There are some genetic sequences which have an effect on methylation and specifically on the waves of demethylation and re-methylation which occur in the early embryo in mammals which are associated with imprinting.But in the case of the Axin fused example the DNA is exactly the same and only the methylation status has changed. If it were the result of a difference in the methyltransferase enzymes then that should have been revealed by the genetic methods used to identify the locus of the mutation.Why are you so fixated on everything just being genetic?TTFN,WK

Hence 'EPI-Genetic' mutation....And I think the fact that methylation is reversible is the point which makes this sort of mutation special. It is heritable, but not necessarily permanent... This makes it starkly different to standard Genetic mutation.Epigenetic Mutation also can only do one thing: Deactivate or Activate a gene. Thats all. Normal genetic mutation has far more to do: http://www.genetichealth.com/G101_Changes_in_DNA.shtmlThis is a good summary of the more common mutations, and you can clearly see some mutations which add to the total amount of 'DNA' present...

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I am not fixated on everything being genetic. I just never knew that there was something other than genetic mutations and I am curious to understand it. I am just trying to learn. =)I based my comments on this quote from Aegist. I am having a hard time trying to keep track of all this new terminology and I assumed that methyltransferases is the agent that is "stopping the expression" which is the phrase that is used.Aegist's comment made it seem that this agent is made from the DNA, I still don't know how else to interpret that comment. I made the connection.Some DNA creates methyltransferases
methyltransferases blocks other DNASo therefore the original "Some DNA" is actually the source of this mutation. Then if that DNA was altered, the methyltransferases would change and the "other DNA" could be un-blocked.That was my impression. It seems that my impression is somehow wrong. I am just curious to understand how this works. We can drop this if it is getting to far OT.I don't know if these questions even make any sense but they would now be:Where does the methyltransferases come from?
If not DNA, how then is the methyltransferases heritable?

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

I guess that is where I am getting confused. How is it heritable? If it is hereditary, how can it be reversed?

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Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

The methyltransferases are proteins produced the same way as any other protein. The methyltransferases themselves are not what supresses the expression of the genes but presence of the methyl groups at the CpG sites.TTFN,WK

Ahuh, I think my wording left somethign to be desired! Methyltransferases are TRANSLATED from the DNA. They aren't made from DNA (as in houses are made from bricks), they are enzymes made from proteins (as all enzymes are) which are put together based on the nucleotide sequence found in the genetic material (made from DNA like cakes are made from recipes).So to try to give a good quick summary if I can: DNA encodes the protein methyltransferase. methyltransferase has an activity which finds a methyl group (methyl - Google Search) grabs it, and attaches it to DNA base pairs. I am not sure how exactly it does this, and it isn't important for the moment. But it is likely to assume there is a mechanism by which this happens (So it can specifically turn genes on and off), and it is also reasonable to assume there is some background non-specific activity (So it might randomly methylate things for no apparent reason. Though this would be very infrequent). In this way the DNA has been 'mutated' because the Nucleotide (the base pair, the A, C G or T) has been altered and unable to function normally. When the DNA is replicated, this alteration is maintained. That is, the copy will also be methylated in the process of replication. Maybe someone could provide more information on how that happens exactly.So, the Methyl group addition to a nucleotide (A, C, G, T) is the mutation that is heritable. Methyltransferase is an enzyme which facilitates this occurance. It alters DNA (mutates it). Why does such an enzyme exist? because it is the means through which organisms control expression of genes. it is how we have one genetic code and hundreds of different cell types. Some genes express in muscle cells, while a completely different set of genes are allowed to be express in neural cells. Methylation is one such method of gene expression contrl.Shane

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CpG refers the nucleotide sequence CG. The p refers to the phosphate backbone and i assume WK writes it as so just so you know with certainty that he is talking about the DNA sequence CG.I assume he refers to CpG specifically because Methyltransferases act specifically on CpG sequence. That is, it won't methylate A's or T's, or ApC's or TpG's or any other 2 base sequence which isn't CpG.

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I don't know what Jazzns knows about DNA translation and whatnot, but I would have interpreted what he wrote in a different manner. as in,
he gets that the enzyme is made by the DNA translation process--essentially making something out of bricks, except you use light for building, dark for instruction.ahh, who knows.

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All a man's knowledge comes from his experiences

Seems to me the factors that drive mutation are the core of evolution. For example,if say, a lowering of ozone in the atmosphere caused intense solar radiation, would this drive an explosion of mutations and thus, new species?

Only if those mutants could survive.See in order for variety to increase (and thus give natural selection something to work with) the varieties must be able to survive. I think of it as the first step in natural selection: Strong selection. If you are born with your brain outside of your skull, you failed the first screening process.Unfortunately, a LOT of mutation tends to do this to organisms. Think of Chernobyl...Are the Russians in that area more likely to evolve quickly, or die horrible deaths?But having said that, the answer is actually Yes. If the world was suddenly bombarded with radiation, it would exert an extreme selective pressure on any organism resistant to radiation. Depending on just how strong it was, either everything would die within generations except the naturally resistant (Cockroaches for whatever reason seem to fall into this category) or the weaker organisms would die and those that are slightly more resistent would live slightly longer. there would then be a gradient pressure for success based on resilience to radiation.But I just realised that selective pressure isn't your concern, its mutation rate. Well, there is without doubt an equilibrium point at which mutation must float in order to maintain optimal hereditary likeness (too much change means too much liklihood of brain outside head scenario) and enough change to allow variation. Variation is necessary due to problems which become apparent when inbreeding and also necessary for when a new virus finds you, you need to ahve differences so that at least one will survive.I think an organism which never mutates would go extinct not too long after an organism which mutates too much every generationI'm sorry I can't give a better explanation that that, but the truth is, once again, it becomes way too complicated (too complicated for ME that is). It becomes a matter of population genetics, statistics, liklihood of survival vs rate of change... etc etc.Shane

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Thanks, Shane. Not so much mutation rate, though that comes into the equation. But the most effective triggers for mutation. If we can grasp which were the main determining factors in the evolution of life, then possibly it points a way to explain sudden extinctions, sudden explosions in population. I realise species diversity is normally an extended process, yet how do we explain the upsurge,say, in plant life? Not just one or a few, but massive diversification world-wide? One would think a trigger was at work favoring that spread.Can`t be all niche selection, can it?

Oh well thats easy

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Not so much mutation rate, though that comes into the equation. But the most effective triggers for mutation
  —nighttrain

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But they are the same thing. I mean, radiation causes mutation, so if you increase radiation, you increase the mutation rate. If you remove the DNA Spell-Checker(TM) then errors in DNA replication will slip through much more frequently and hence higher mutation rate... If you identify a cause of mutation (and there are many), and you increase that (or remove the safety, or whatever the case is) than you will increase the mutation rate.

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how do we explain the upsurge,say, in plant life
  —nighttrain

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Darwin answered this in origin of the Species, and I don't see why it would have changed in the interveneing time.A surge in population will occur because the organism is very successful. (Humans for example) A good example for the purposes of understanding would be one of the deers in Africa (cant think of a species name...you know the ones, eat grass watching out for lyons) undergoing a mutation which made it twice as fast as all of the other other deer and twice as fast reaction wise. That dear will be GREAT at surviving predators. It will prosper like no dear has previously prospered (due to no predator) and accordingly it will produce many offspring. It would outcompete the non super-deer and they would eventualyl die off from predation because they would always be the slowest.The super deer would then start to face its first selective pressure: Competition with itself. It would have to compete with other super deer for food sources. Due to overpopulation they will start to disperse, walking further and further outward from their origin. They would displace more and more slow dear and continue to grow their numbers.What happens in essence is they will over time grow to such large numbers and displace so many competing species that they would be the dominant species. With so many of them, the variation would be huge. Just statistically. how much variety can you get out of 5 people? How much variety can you get if you had 2 billion people? the super deer would start showing variation from general sexual recombination as well as normal mutation. Eventually they would fill all of their niche environment and start competing with themselves.Some would be pushed right out into different niches. Mountainous. Jungle. Sea. marsh.... different environments which they weren't optimised for, and so only some would survive there...and hence natural selection would start to use the MASSIVE variety with which it is presented to carve out new species.Its a bit of a long winded story, but hopefully it is simple enough.Short version; Successful species numerates drastically, becomes TOO successful for its own good and is forced to cmopete with its own sepcies for food etc. Species is pushed out into non-ideal conditions and selective pressure is applied to the massive numbers and the winners are allowed to proceed to the next round. Speciation may take root where appropriate.

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