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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
I thought you were asking why muller's ratchet didn't provoke the extinction of bacterias ? I'm asking why bacteria don't go extinct as a result of these mysterious, impossible mutations which cause extinction but are invisible to natural selection, when they are more vulnerable to the accumulation of deleterious mutations and breed much faster. If we don't observe it in them, why should it affect anything else?
I think it is gonna be very difficult to discuss this with your aggressive behavior ... You mean, I point out where you're wrong, ask you for evidence, that sort of thing?
... coupled with the fact that you haven't read the book. Feel free to reproduce his arguments. Incidentally, have you read Kimura?
Dr. Sanford doesn't simply apply Muller's ratchet on sexual species, he ellaborates the concept of mutation accumulations to sexual species. This is very different. It is. Muller's rachet specifically applies to asexual organisms; the idea was put forward as one reason why sex is biologically advantageous. Calling some putative process that affects sexually reproducing organisms by the name "Muller's rachet" is sheer obfuscation.
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Percy Member Posts: 22508 From: New Hampshire Joined: Member Rating: 5.4 |
From Message 83:
slevesque in Message 83 in reply to Dr Adequate writes: The interpretation creationist do of it is debatable, but for that you'll have to read the book instead of just reading the critics on amazone.com From Message 89:
slevesque in Message 89 in reply to Dr Adequate writes: I think it is gonna be very difficult to discuss this with your aggressive behavior coupled with the fact that you haven't read the book. If someone actually reads the book that will be a nice bonus for you, but don't expect it to happen. The Forum Guidelines require that you make your arguments in your own words:
You're referencing a book instead of a link, but the same principle applies. Make the argument in your own words. The purpose of debate is so you can assess how effectively *you* can construct and support an argument, not someone else. About the funny characters, were you trying to say ‘(μ) or something like that? --Percy
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slevesque Member (Idle past 4671 days) Posts: 1456 Joined: |
Now, a new neutral variation thrown up by mutation is one of 2N versions (some identical) of the site, where N is the size of the population (the 2, of course, is there because we are dealing with diploid organisms). Because the variation is neutral, this means that it has no better nor worse chance of going on to fixation in the gene pool than the other 2N-1 versions of the site. It follows that when it first arises, its probability of fixation is 1/2N. A more detailed version of the proof will be found here. Now, let the probability of the mutation in an individual be . Then the probability of it arising in a generation will be 2N. So the probability, in any generation, that such a mutation will arise and eventually go on to fixation is 2N/2N; and since we can cancel the 2N on the top and bottom of this fraction this works out to be just equal to . I was talking about that part, with the u The 51 mutations fixed per generation, is that threw genetic drift ? Edited by slevesque, : No reason given.
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slevesque Member (Idle past 4671 days) Posts: 1456 Joined: |
I'm asking why bacteria don't go extinct as a result of these mysterious, impossible mutations which cause extinction but are invisible to natural selection, when they are more vulnerable to the accumulation of deleterious mutations and breed much faster. If we don't observe it in them, why should it affect anything else? We don't observe it in them because the no-selection zone is quasi inexistant for them, and so even nearly-neutral mutations can be detected by natural selection. hence they are not really nearly-neutral. I think Kimura uses the term 'effectively neutral' for the mutations that are not subject to natural selection, Dr. Sanford uses the term nearly-neutral, but he is talking about the same mutations (cannot be selected for). There is much more 'effectively neutral' mutations in humans then in bacteria, because of the difference in noise.
You mean, I point out where you're wrong, ask you for evidence, that sort of thing? I have no problem with that. But I have to say that the very first of your comments I read (on other threads) were not of that kind which you are speaking of. Much more arrogant and aggressive.
It is. Muller's rachet specifically applies to asexual organisms; the idea was put forward as one reason why sex is biologically advantageous. Calling some putative process that affects sexually reproducing organisms by the name "Muller's rachet" is sheer obfuscation. You have to remember two things: Muller developped his idea of ratchet in asexual species, but he was aware that the same could happen in sexual species. He was a leading adovcate of eugenics, and had a deep concern for human genetic deterioration (hence the eugenism). He thought mutations were extremely rare, and so could be dealt with one at a time threw selection. Obviously, his concern was that with the arrival of medecine etc. Natural selection would be much less efficient in the human species, and so mutations would accumulate.
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slevesque Member (Idle past 4671 days) Posts: 1456 Joined: |
The accumulation of mutations in sexual species is not a farfetched idea either. Take a look at the abstract of this paper:
Loewe, L. 2006. Quantifying the genomic decay paradox due to Muller's ratchet in human mitochondrial DNA. Genet. Res., Camb 87:133-159 Abstract:
The observation of high mitochondrial mutation rates in human pedigrees has led to the question of how such an asexual genetic system can survive the accumulation of slightly deleterious mutations caused by Muller's ratchet. I define a null model to quantify in unprecedented detail the threat from extinction caused by Muller's ratchet. This model is general enough to explore the biological significance of Muller's ratchet in various species where its operation has been suspected. For increased precision over a wide range of parameter space I employ individual-based simulations run by evolution@home, the first global computing system for evolutionary biology. .After compiling realistic values for the key parameters in human mitochondrial DNA (mtDNA) I find that a surprisingly large range of biologically realistic parameter combinations would lead to the extinction of the human line over a period of 20 million years — if accepted wisdom about mtDNA and Muller's ratchet is correct.. The resulting genomic decay paradox complements a similar threat from extinction due to mutation accumulation in nuclear DNA and suggests evaluation of unconventional explanations for long-term persistence. A substantial list of potential solutions is given, including compensatory back mutations, mutation rate heterogeneity and occasional recombination in mtDNA. Future work will have to explore which of these actually solves the paradox. Nonetheless, the results presented here provide yet another reason to minimize anthropogenic increase of mutation rates.. Article Abstract Mitochodrial DNA is an asexual system, and so subject to Muller's ratchet. However, Loewe makes it abundantly clear that nuclear DNA (which is not asexual) can also be subject to mutation accumulation. This is exactly what Dr. Sanford is talking about, an arguing for. You can ask, if mutations are accumulating in the human genome, why aren't we seeing its effects ? Sanford does not talk about this in his book, but personnally I think we can see repercussions in this accumulation. From a personnal experience, the region where I live, saguenay-lac-saint-jeanthat are unique to the region. These are not near-neutral by any means, because each of them are very serious . But because they are recessive (as are most mutations I believe) they have been accumulating in the region at an alarming rate. Of course none have become fixed in the population yet, but it is a very alarming situation, to the point that there has been a lot of research money invested to 'fight' this. Another example I can think of is the recent trend to ban marriage between cousins in Europe, which is becoming a hot topic I think over there. It seems that similar mutations are becoming more and more frequent, to the point that even cousins inter-marriage are having an increasing probability of birth defects. This is in stark contrast to the culture of even 200 years ago, where marrying a cousin was common but was not known as a source of child defects. If it is now seen as a problem, it is because mutations have become more widespread in the population. Edited by slevesque, : No reason given. Edited by slevesque, : No reason given. Edited by Admin, : Shorten long link.
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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
We don't observe it in them because the no-selection zone is quasi inexistant for them, and so even nearly-neutral mutations can be detected by natural selection. Saying this is no substitute for evidence.
You have to remember two things: Muller developped his idea of ratchet in asexual species, but he was aware that the same could happen in sexual species. Quotes, please?
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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
Mitochodrial DNA is an asexual system, and so subject to Muller's ratchet. However, Loewe makes it abundantly clear that nuclear DNA (which is not asexual) can also be subject to mutation accumulation. Where does he make it "abundantly clear" that mutations in nuclear DNA, invisible to natural selection, can accumulate to cause extinction?
From a personnal experience, the region where I live, saguenay-lac-saint-jeanthat are unique to the region. These are not near-neutral by any means, because each of them are very serious . But because they are recessive (as are most mutations I believe) they have been accumulating in the region at an alarming rate. Of course none have become fixed in the population yet ... The reason that they are unique to the region is because of the founder effect, and the reason that they will never become fixed is heterozygote equilibrium.
Another example I can think of is the recent trend to ban marriage between cousins in Europe, which is becoming a hot topic I think over there. I've never heard of such a movement.
It seems that similar mutations are becoming more and more frequent, to the point that even cousins inter-marriage are having an increasing probability of birth defects. Evidence?
This is in stark contrast to the culture of even 200 years ago, where marrying a cousin was common but was not known as a source of child defects. If it is now seen as a problem, it is because mutations have become more widespread in the population. No, it's because now people know about it. Mutations which cause birth defects are, in any case, not invisible to natural selection and so have nothing to do with Sanford's fantasies.
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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
I was talking about that part, with the u Ah, I see. That's a mu (μ) not a u. That represents the probability of any particular single nucleotide substitution occurring.
The 51 mutations fixed per generation, is that threw genetic drift ? Yes. Edited by Admin, : Fix special character so it doesn't become a smiley.
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slevesque Member (Idle past 4671 days) Posts: 1456 Joined: |
the evidence is that bacteria species do not go extinct because of Muller's ratchet
For the quote: Muller, HJ. 1950. Our load of mutations. Maer. J. Human Genetics. 2:111-176 (page149-150)
quote: Thus why he was a proponent of eugenics. Note also that, if I'm not mistaken, we now know that the mutation rate is at least 1000-fold higher, and that fertility is on the decline, which in itself is compelling. Edited by slevesque, : No reason given. Edited by slevesque, : No reason given.
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slevesque Member (Idle past 4671 days) Posts: 1456 Joined: |
Where does he make it "abundantly clear" that mutations in nuclear DNA, invisible to natural selection, can accumulate to cause extinction? "The resulting genomic decay paradox complements a similar threat from extinction due to mutation accumulation in nuclear DNA " Its is as clear as you can get
No, it's because now people know about it. People would have known of birth defects caused by sister-brother marriage, but would have been ignorant of cousins marriage birth defect ? It seems more logical to me that it was less of a problem in those days.
Mutations which cause birth defects are, in any case, not invisible to natural selection and so have nothing to do with Sanford's fantasies. Of course, if we are talking about a dominant gene, then it cannot accumulate. But if the birth defect comes fro ma recessive gene, then it can accumulate, and as it accumulates, it becomes more frequent that two individuals have the gene and give birth to sick children.
I've never heard of such a movement. It isn't a movement (yet, I suppose) but it is being talked, especially in England. It is because of the Islam, in which cousins marriage is encouraged I think (Mohammed married his cousin). And so the problem is more evident. Here in North America it is no longer popular to marry our cousins (thankfully lol), but my intuition would tell me that if it would still be, then we would be facing the same problems as in europe.
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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
the evidence is that bacteria species do not go extinct because of Muller's ratchet That would be my point.
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Dr Adequate Member (Idle past 315 days) Posts: 16113 Joined: |
"The resulting genomic decay paradox complements a similar threat from extinction due to mutation accumulation in nuclear DNA " Its is as clear as you can get Ah, I see. Nonetheless, he seems convinced that this does not actually happen.
People would have known of birth defects caused by sister-brother marriage ... Would they? It's not like it happens that often. What with being illegal, and all that.
Of course, if we are talking about a dominant gene, then it cannot accumulate. But if the birth defect comes fro ma recessive gene, then it can accumulate, and as it accumulates, it becomes more frequent that two individuals have the gene and give birth to sick children. Up to heterozygote equilibrium.
It isn't a movement (yet, I suppose) but it is being talked, especially in England. I'm English, I've never heard of this.
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Theodoric Member Posts: 9207 From: Northwest, WI, USA Joined: Member Rating: 3.4 |
slevesque writes:
Ok do you have any evidence for the things you say. Cousin/cousin is not huge cause of birth defects.
where marrying a cousin was common but was not known as a source of child defects. If it is now seen as a problem, it is because mutations have become more widespread in the population. Here is some real science on the issue
quote: Here is the original.
quote: Facts don't lie or have an agenda. Facts are just facts
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Taq Member Posts: 10085 Joined: Member Rating: 5.6 |
Three points.
1. Muller's ratchet can be overcome through recombination. While bacteria are considered asexual they do exchange DNA on occasion. 2. Beneficial mutations can compensate for deleterious mutations. This is exactly what was found in this study:
quote: In other words, mutations that compensate for the deleterious mutations will be selected for. 3. A genome can only handle a certain amount of deleterious mutations. At some point new deleterious mutations will be face strong selective pressures. This appears to be the case in the primary endosymbiots of lice (this study).
quote: So it would seem that there are at least 3 mechanisms by which asexual genomes can avoid the effects of Muller's Ratchet.
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bluegenes Member (Idle past 2508 days) Posts: 3119 From: U.K. Joined: |
Dr Adequate writes: I'm English, I've never heard of this. I have. It's not Muslims as such, but people from some areas of Pakistan (who happen to be Muslims) that have produced a lot of migrants. Here (link below), it says that the birth defect rate is thirteen times the average, which doesn't seem to fit the U.S. research for random cousin marriages Theodoric linked to above. However, it may be a cumulative effect in communities that constantly do it (you're marrying your first cousin, second cousin and aunt/uncle once removed all at the same time!!!!). BBC NEWS | Programmes | Newsnight | The risks of cousin marriage
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