Mutation and its role in evolution: A beginners guide

The questions almost make sense, but I think I detect an underlying confusion about the whole process.The 'Enzymes' which i think you are referring to are the Methyltransferases. They are enzymes present in all cells with their own tasks and they are not mutations in themselves in anysense. They are the mediators of the form of mutation called Epigenetic mutation.What these enzymes do is attach a molecule (a methyl group) to a DNA base pair thereby slightly altering the chemical nature of that base pair and interupting how it normally functions. This is not permanent (unlike genetic mutations) and can be undone quite easily by another enzyme (If my memory serves me correctly, perhaps I should get some references for this before I state it ).So, these enzymes change the way DNA works (at that particualr base pair) thereby stopping the expression of any gene present at that site. So methylating a gene is basically turning it 'OFF' which is similar to mutating it away...making it no longer exist. An organism with a gene turned off is functionally the same as an organism without that gene. The obvious difference being in the fact that the organism with the gene turned off can turn that gene back on by a simple reaction while the organism without the gene can't get the gene back!The heritability of the enzyme is not the question. the enzymes (methyltransferases) are made from the DNA (which is heritable). The heritability of the "Mutation" is that once these methyltransferases has methylated a genetic site, that methylation is heritable. In other words, once a site has been inactivated, it will be inactivated in the offspring and their offspring and so on until something happens which causes the gene to be turned back on. This is the heritability of the mutation.Hopefully the answer to your third question is already clear, but just in case: The enzyme itself is virtually irrelevent (it isn't even necessary for the enzyme to exist for DNA to be methylated!). The mutation is the Methyl-group addition to the DNA base pair which changes the chemical structure of that nucleotide. This change in chemical structure affects the way that DNA sequence acts, and therefore affects how it is expressed, and therefore affects the phenotype.I hope these answers make sense! Please correct me where appropriate others who are more versed in this topic than I!ShaneEdited by Aegist, : clarity

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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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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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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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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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