Some mutations sound too good to be true

The key is "if". Some populations will recover rapidly, for a variety of reasons (including large numbers of offspring, fast breeding cycles, lack of predation). Other populations will not recover rapidly, again fro a variety of reasons. Such a population is at higher risk for extinction, yes. Remember, a population that doesn't make it out of the bottleneck is, by definition, extinct.

A common example is any experiment where a population of bacteria (again, getting back to bacteria - they're easy to rear, have fast generation times, and their genetic mechanisms are almost completely the same as ours) is raised from monoculture; that is, from the asexual reproduction of one single individual.One individual bacterium has only one allele per gene, unlike sexual creatures. They reproduce clonally, so, the gene pool that develops as the organism reproduces should never expand beyond one allele per gene. However we do observe the gene pool expand in diversity over time to include multiple alleles per gene; we know that these new alleles are not inherited from the ancestor and they're not coming in from outside (we've sealed the experiment), so mutation of existing alleles into new ones is the only explanation for this increased genetic diversity. An allele is a specific "version" or configuration of a given gene; for instance "eye color" would be a gene, but "blue eyes" or "brown eyes" are alleles. (And "green eyes" is not itself an allele but the result in having both the allele for blue eyes and the allele for brown eyes. Fun fact.)In the gene pool of the above experiment - gene pool is the term for the scope of different alleles possessed among all members of the population - we see the number of alleles per gene expand from one per gene in the original ancestor - one per gene is all the alleles one bacterium can contain - to multiple alleles per gene.Since there's no other source of new alleles into this gene pool, and we're observing alleles that we know aren't already there, there's only one explanation - individuals are gaining genetic sequences that they did not inherit from their parent. That's mutation.And remember that it's diversity that increases, not neccesairly variability. Diversity is the term for the amount of variation between individuals in a population; variability would be, I suppose, a measurement of how likely mutations are to occur at any given gene locus.As for increasing the viability of the species - you can pretty much see any resistance adaptation experiment for that.

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I tend to think of anything's being missing as a negative effect of mutation, don't you?

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Well, no, I don't.For example, partial to total immunity to the AIDS virus seems to be the result of a mutation in receptor (portal) protein of white blood cells that have lost the ability to let the virus in. More here.

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But of course under some circumstances it can confer a benefit,

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Right!

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and in this case it appears to be neutral as far as consequences go.

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From a reproductive success standpoint, yes, it was neutral.If I had been alive way back when selection pressure from nature was much more influential for the human species, I most likely would have reproduced (at least once) quite a few years before my wisdom teeth emerged.This message has been edited by schrafinator, 09-28-2005 08:18 AM

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Actually there is new evidence that the lack of wisdom teeth may be beneficial in that there is a lower risk of gum disease (I know, yucky topic). This is important, as gum disease can cause heart disease and pregnancy problems among other things. Sorry to rub it in, but this is yet more evidence of bad design imo.

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I'd just like to point out that this is an excellent example of how a mutation that is neutral or beneficial in certain circumstances can become deleterious in others.

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Actually there is new evidence that the lack of wisdom teeth may be beneficial in that there is a lower risk of gum disease

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Since I had my wisdom teeth removed because I kept getting gum infections the link is painfully clear to me.(I recommend an ibuprofen/codeine mix for dealing with dental pain - nothing less worked for me).

I don't have a link but this kind of information is determined using molecular clocks - that is, the accumulation of mutations. By comparing the genetic diversity of cheetahs to their closest relatives and the number of accumulated mutations in the respective species it is possible to date a bottleneck with some precision. Mutation rates are relatively constant within a species and between similar species back to the point of a common ancestor. The beauty of this methodology is that we can directly measure accumulated mutations in extant species. This number can be compared to the number of years since the most recent divergence of two species (as determined by radioisotope dating) and thus we can determine which of the species had a bottleneck and when it occured.

Radioisotope dating of what exactly if I may ask?Also, doesn't all this depend completely on the assumption that the rate of mutation has been constant over time? That is, there is no actual observation that can be pointed to, it is merely that the present rate of mutation is extrapolated backward in time?

And these may be anything from deleterious to beneficial, right?And, just to confirm this, the CAUSE of mutation is mistakes in DNA replication? I've beem using the two synonymously but if that's confusing I will stick to "diversity."This message has been edited by Faith, 09-28-2005 07:52 PM

Mutation is something that can be observed. Yes, it does depend on extrapolating backwards. Why shouldn't it? If we can't extrapolate something we should all just accept Last Thursdayism and be done with it. No, that's A cause, not THE cause of mutagenesis. There other causes of mutation, most noticabley mutagens, agents such as chemicals and radiation tha cause mutations.

But only in the present, right? That is, you can't look at a genome and reliably point to former mutations can you? I would suppose that possibly some might be apparent, but since the assumption is that evolution is made possible through mutation, then all of it would be ASSUMED to have at one point derived from mutation, but actually OBSERVING this is impossible except occasionally in the present. But the rate may have increased or decreased over time rather than always having been the same rate that is now observed, as is assumed. If you don't KNOW that the rate has always been constant, but merely assume it, mightn't your timing of the bottleneck be wrong? Great. Thanks. I thought some were being a bit too exclusive about this cause, but possibly I misunderstood.And in the case of bacteria?

Right. The vast majority are truly neutral in the sense that they have no end effect on the organisms phenotype - i.e. the physical characteristics of the organism - most of the rest are deleterious to some degree (assuming a trivial environment), and a few are beneficial. "Mistakes" is kind of a loaded, subjective term; but yes, mutations occur during DNA replication when, for various chemical reasons, the copy or "daughter" DNA is different from the source DNA.AbE: Oops, an above poster is correct - some mutations also happen during the normal course of the non-dividing cell (the "interphase" of the cell). DNA can be damaged by chemical or radiological agents - "mutagens" - and, during the repair, changes to the genetic sequences may occur. I think that's the most accurate, least misleading term.This message has been edited by crashfrog, 09-28-2005 08:10 PM

Interesting. It has occurred to me to wonder whether this really is a mistake or possibly something "normal" at least in some cases. The phrase "for various chemical reasons" could contain some fascinating information. Terrif. The Mystery of Mutation is starting to become clearer. What the thread was for.

You're not going to understand how mutations occur if you don't understand the structure of DNA and the process of DNA replication.But, just to head you off at the pass, mutations are always random. Random in the sense that their location and result cannot be predicted in the sense of "this generation of individuals is going to have that mutation at that location." It's certainly the case that certain genetic locii are more prone to mutation than others; this is not a programmed function of the cell or of genetics but a consequence of the chemical properties of the four bases, as well as structural properties of some genetic sequences.For instance, sequences of the same base repeated several times - i.e. "TTTTTT" - are more likely to experience certain types of mutation than nonrepetitive sequences. This is again, not evidence of certain mutations being programmed, but a natural consequence of the way DNA replication works. It's not a big mystery. But it's not going to be terribly clear to you absent a working understanding of how DNA is structured and how it is able to be replicated.

Yes, you can. You just can't do it from a single sample. There's such a thing as indirect observation. Remember the old koan: "If a tree falls in the forest, does it make a sound?" We can infer that the tree made a sound (if we define "sound" as pressure waves) even if there was no one that recorded hearing it. Constant rate is NOT assumed. That's why you look at *several* loci that are not subjected to selection (that "junk" DNA). That's also why there is an error margin.There's an implicit assumption in that statement that thousands of scientists are too stupid to notice that the rate may not be constant. I know that's not how you mean it, but that is what you are saying. Same molecule, same mechanisms.

Is it too complicated to say how a number of samples can show this? Certainly, but you have to have reliably observed mutation (heard trees falling) of a kind and at a rate, to support the idea of evolution in order to make a reliable extrapolation from it, and extrapolating to the past where all kinds of things might have been different (unlike unwitnessed trees falling in unwitnessed forests which only have to obey the laws of physics) adds another dimension of possible error. What I assumed is that the principle of uniformitarianism governs many scientific estimates of time, especially in the absence of positive corroborating factors. Now you are saying that there are other indicators of a (relatively?) constant rate of mutation to be found in the junk DNA?