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Author | Topic: Genetic load: can someone explain? | |||||||||||||||||||||||||||||||||||||||
NosyNed Member Posts: 8996 From: Canada Joined: |
Thank you. I understand all the words now and the different cases makes sense.
I would guess that the independent or synergistic effect cases are the more common? I think I could now tie this back to the OP but I'm going out (and would rather someone else (who might get it right) did it first. (Later I will try). Then I'll have to review the information to see the evidence for the synergistic case in humans.
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NosyNed Member Posts: 8996 From: Canada Joined: |
From the OP:
If mutations interact multiplicatively, So this basic assumption must be met. If they are synergistic then deleterious mutations do not pile up and become such a problem. That is the average fitness does not drop to as low as 0.05. Right? However, I know realize that I don't know how "average fitness" is determined or what it means. It seems to suggest that if it is 0.5 then half of offspring survive to reproduce. That makes some kind of sense. Now then how do we decide if it is actually synergistic? It makes sense to me that it might be. Obviously, there will be cases where having one moderately deleterious mutation might not be enough to stop reproduction but a second one is fatal? Correct?
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Now then how do we decide if it is actually synergistic? By post hoc measurements of survival or mating success, the same way we would determine what the fitness is for an individual mutation. If we can measure the fitness cost for each deleterious mutation independently and together we can see if the combined fitness cost is multiplicative or synergistic.
Obviously, there will be cases where having one moderately deleterious mutation might not be enough to stop reproduction but a second one is fatal? Correct? Certainly. The most obvious case, although not a very likely one, is if if you had 2 distinct deleterious mutations in different allelic copies of the same gene, where only 1 wild type allele was required for normal wild-type fitness. Each in isolation would have little effect but having the 2 simultaneously would be severely detrimental. It is much harder to call if the deleterious mutations in question are in completely different parts of the genome and possibly not even involved in the same developmental/metabolic pathways. This is why we can only really use post hoc methods to investigate the interactions of multiple mutations. The other research approach taken relies principally on extensive theoretical modeling but obviously this can't tell us what situation actually obtains in human genetics. For an idea of how complicated investigating epistasis is, even in the comparatively simple context of E. coli, take a look at Beerenwinkel et al.(2007).
Beerenwinkel et al writes: Epistasis occurs whenever mutations interact non-linearly with one another, and it represents a major challenge in describing the mathematical structure of real fitness landscapes. With epistatic interactions, the combined effect of two or more mutations on fitness may be greater than, less than, or opposite in sign to expectations obtained by combining their separate effects. A growing body of empirical research indicates that epistasis is very common in nature [references removed]. However, a complete mathematical description of epistatic interactions has not been forthcoming for any system because the forms of epistasis appear to be diverse, idiosyncratic, and hence complex. TTFN, WK
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Phydeaux Junior Member (Idle past 5203 days) Posts: 13 Joined: |
So, let me see if I've got this right. The idea is that, if deleterious mutations exhibit synergistic epistasis, the fitness will eventually stabilize due to selective pressures. Correct?
Whether this idea is correct or not seems to be very important to both sides of the EvC debate. Dr. John Sanford in his book Genetic Entropy & the Mystery of the Genome made an argument against the leveling of the deterioration and I think this could be the most important part of his book and thus the creationism movement. I'm hoping you know basically what the book is talking about already, because I don't want to quote a lot of the book if I don't have to. Read the chapter - Crow to the rescue? - if you can. Here is what he said in response to this model:
quote: I can try to get more information on the exact numbers he uses later if necessary, but a question naturally arises regardless: Is the equilibrium (so to speak) of the population soon enough as to prevent problems for the evolutionary theory? Would it be correct to assume that we simply do not know yet? Dr. Sanford continues:
quote: I'm not sure if this is correct or not, but on first glance it sound reasonable. Basically, his claim is that natural selection is not powerful enough to select against an organism with the most mutations because all mutations are not equal. The individuals with the most harmful mutations will be weeded out while the organisms with the most mutations will be left behind. Whether that poses a problem for the evolutionary model or not I am unsure, but he sure seem to think so. Interestingly he goes on to discussion synergistic epistasis:
quote: This was actually my first impression of this as well. I'm curious as to if synergistic epistasis will actually help or harm the theory. How exactly does an increase in effect of deleterious mutations help? Is this supposed to make the mutations more visible to selection? Let me go ahead and put his final word because I already discussed the others:
quote: He goes on to talk about problems he has discussed earlier such as near-neutral mutations. One of his assumption seems to be that the mutations are not near-neutral in the graphs that produce a leveling out of the curve. Is that correct? Dr. Sanford seems to be a well respected evolutionary scientist and certainly knows more than me, so I want to believe he is correct, but he is not a population geneticist, so it is well possible he is incorrect. What do you guys think? Again, I tried to quote only that which was necessary for debate, so If you need clarification, simply ask. Edited by Phydeaux, : No reason given.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined:
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I'll respond in more depth when I have the time, just in the meantime I would say. I still don't see how this is necessarily a problem for evolution? It might be a problem for the human race when it becomes extinct but I don't see why it is a problem for evolution.
TTFN, WK
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Phydeaux Junior Member (Idle past 5203 days) Posts: 13 Joined: |
quote: Well, it really depends. If the build up of deleterious mutations is only due to medical advances, then it is not a problem for evolution, but if deleterious mutations are always building up regardless of medical advances, then this is obviously just as much a problem for australopithecus as it is for humans. We can't evolve if genetic load kills us first. Further more, we can't build up function building mutations if we have more deleterious mutations than function building mutations. Edited by Phydeaux, : No reason given.
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Coyote Member (Idle past 2107 days) Posts: 6117 Joined: |
If the build up of deleterious mutations is only due to medical advances, then it is not a problem for evolution, but if deleterious mutations are always building up regardless of medical advances, then this is obviously just as much a problem for australopithecus as it is for humans. We can't evolve if genetic load kills us first. Further more, we can't build up function building mutations if we have more deleterious mutations than function building mutations.
If evolution, and these deleterious mutations, have been going on for several billion years, I wouldn't worry about them too much. We're doing just fine in spite of being proclaimed doomed because of this problem. Where deleterious mutations would become a real problem is when one believes that the buildup of these mutations has been going on for just 6,000 years (since The Fall), and that its been all downhill since then. But since there is no empirical evidence for either a 6,000 year old earth, or a "fall from perfection," and since the evidence shows billions of years of successful evolution, we don't need to worry about it, eh? Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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Phydeaux Junior Member (Idle past 5203 days) Posts: 13 Joined: |
quote: Well, first, you just ignored old earth creationism/ID. Second, the question of what the evidence says is exactly the question we are here to discuss. The mutation rate and genetic load is part of the evidence. I think it is rather foolish to ignore evidence in any case. Sure, pointing to other evidence and saying this evidence over here is more convincing is perfectly reasonable, but you should also acknowledge that there is evidence against the theory (if this is actually evidence against the theory).
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Coyote Member (Idle past 2107 days) Posts: 6117 Joined: |
Well, first, you just ignored old earth creationism/ID. With old earth creationism we have billions of years of evolution, and no "fall" about 6,000 years ago. The argument that deleterious mutations are going to get us "real soon now" after billions of years doesn't scare me in the least.
Second, the question of what the evidence says is exactly the question we are here to discuss. Evidence, yes. Scripture and "divine" revelation are not evidence. The idea of "the fall" is a religious belief, not a scientific finding.
The mutation rate and genetic load is part of the evidence. I think it is rather foolish to ignore evidence in any case. Sure, pointing to other evidence and saying this evidence over here is more convincing is perfectly reasonable, but you should also acknowledge that there is evidence against the theory (if this is actually evidence against the theory).
If the deleterious mutations are suddenly going to get us, with this "genetic load," after billions of years, perhaps we could be provided with a mechanism, and a reason for such a drastic change after all this time. I think the belief in a young earth and "the fall" is behind this so-called science. With an old earth and no "fall" there doesn't seem to be a problem at all, no matter what creationist authors claim. Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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slevesque Member (Idle past 4641 days) Posts: 1456 Joined: |
You seem to be equivocating the fact of evolution with the theory of evolution, invoquing that since we know the former is ''true'' (I don't think it is, but from your point of view) then obviously the later is true as well.
But it doesn't follow. Neo-Darwinian evolution as a theory uses two mechanisms: mutations and natural selection. This is supposed to be able to explain the fact of evolution shown by the fossil record, amongst other things (which by the way, shows much more ponctuated equilibrium in my humble opinion.) But if Mutation+NS is being discovered to be unable to provide the fact of evolution, then other avenues must be searched. Possibly a third mechanism that, added with the two others, can be shown to produce the evolution of a population. At this stage, the fact of evolution has not being challenged. But I do not think, and you will probably agree with me, that you can really bring up the fact of evolution, and through it protect the Neo-Darwinian theory of evolution. If simple mutations+NS is shown to be unable to produce the fact of evolution, than other avenues must be searched. Rereading your post before sending mine, this is not exactly what you are doing. I still post it anyways as I find it a good addition to the overall discussion.
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slevesque Member (Idle past 4641 days) Posts: 1456 Joined: |
I think he was more talking about the evidence brought up by modern genetics. (number of mutations per person per generation. Beneficial to deleterious ratio of these mutations. The danegrs of mutational meltdown, etc.)
You always seem to be bringing up the fall for whatever reason I don't know. And you tag it here as the evidence Phydeaux is talking about, which it clearly was not.
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slevesque Member (Idle past 4641 days) Posts: 1456 Joined: |
I think Dr. Sanford sometimes peer-reviews papers in the domain of population genetics, so he is pretty qualified in the field I would guess.
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Phydeaux Junior Member (Idle past 5203 days) Posts: 13 Joined: |
I think you misunderstand what I am saying. I never said anything about the fall. The timing of a genetic meltdown has nothing to do with the age of the earth or the fall. The meltdown has to do with the rate which deleterious mutations are accumulating.
Edited add: Just so you know, I'm not a YEC nor a OEC. I'm not even an ID proponent. I have yet to make up my mind on these issues because there is just so much left to learn. I lean towards those things and I will make arguments for those things, but I will not claim I know one of these are true because I do not know. I only defend these ideas so the theories can be tested through debate. So, please don't assume I support the fall or Noah's Ark etc... Edited by Phydeaux, : Edited add
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Phydeaux Junior Member (Idle past 5203 days) Posts: 13 Joined: |
He is pretty qualified because he was a plant geneticists, but the general idea I get from his book (I don't know if you have read it) is that he always looked up to the population geneticists as geniuses of whom he was not worthy to question. Not very long before he published his book he was converted into a YEC. I assume that it was then he first really started to dig through the literature of the population geneticists because he presents the finds as if he was surprised to find it like if he never would have expected he didn't know about it for all the years of his research. For this reason I question how well he understand population genetics. He certainly is qualified, but I think his arguments should certainly be read with caution.
Edited by Phydeaux, : No reason given.
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PaulK Member Posts: 17822 Joined: Member Rating: 2.2 |
I think that you miss the point. The timing will be affected by the start point.
If your quote accurately reflects Sanford's views, he says:
...the population plummets essentially to zero... in just 300 generations.
Obviously the human population is not "essentially zero", so humans must have been around for less than 300 generations, right ? That would fit quite happily with a timescale of 6000 years, but not with an Old Earth timescale (which cannot be much less than 200,000 years).
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