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Author | Topic: How long would it take for a novel alelle to be fixated in a population? | |||||||||||||||||||||||
CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Things such as Haldane's dilemma are relevant to the thread. I would ask for participants of the thread to have benefitial mutations as a given. There is a thread of that already.
Unless selection is very intense the number of deaths needed to secure the substitution by natural selection, of one gene for another at a locus, is independent of the intensity of selection. It is often about 30 times the number of organisms in a generation. It is suggested that in horoletic evolution, the mean time taken for each gene substitution is about 300 generations. This accords with the observed slowness of evolution.
IIS 10.0 Detailed Error - 404.0 - Not Found Creationists like ReMine say that it refutes evolution.This paper is very old and even Haldane admitted that there might be errors in his calculations. If Haldane was wrong then what model was able to correct it? Edited by CoolBeans, : No reason given. Edited by CoolBeans, : No reason given. Edited by CoolBeans, : No reason given. Edited by CoolBeans, : No reason given.
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Admin Director Posts: 13017 From: EvC Forum Joined: Member Rating: 1.8 |
Fixation is related to alleles, not features.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Ok I fixed my mistake.
Another thing to note, is that it may only apply to mammals since they reproduce slowly. Edited by CoolBeans, : No reason given. Edited by CoolBeans, : No reason given.
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Admin Director Posts: 13017 From: EvC Forum Joined: Member Rating: 1.8 |
Thread copied here from the How long would it take for a novel alelle to be fixated in a population? thread in the Proposed New Topics forum.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Imagine a population of 100,000 apes, the putative progenitors of humans. Suppose that a male and a female both received a mutation so beneficial that they out-survived everyone else; all the rest of the population died outall 99,998 of them. And then the surviving pair had enough offspring to replenish the population in one generation. And this repeated every generation (every 20 years) for 10 million years, more than the supposed time since the last common ancestor of humans and apes. That would mean that 500,000 beneficial mutations could be added to the population (i.e., 10,000,000/20). Even with this completely unrealistic scenario, which maximizes evolutionary progress, only about 0.02% of the human genome could be generated. Considering that the difference between the DNA of a human and a chimp, our supposed closest living relative, is greater than 5%,2 evolution has an obvious problem in explaining the origin of the genetic information in a creature such as a human. Haldane's dilemma has not been solved - creation.com
Haldane calculated that no more than 1,667 beneficial substitutions could have occurred in the supposed 10 million years since the last common ancestor of apes and humans. This is a mere one substitution per 300 generations, on average. If any of this is true then it would be a problem.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Here is ReMine's paper on the subject.
http://creation.com/images/pdfs/tj/j19_1/j19_1_113-125.pdf
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PaulK Member Posts: 17825 Joined: Member Rating: 2.2 |
THere are two things you need to know.
First, Haldane's figures are rough estimates. To pass them off as definite facts is irresponsible, at best. Second, Haldane's dilemma assumes "hard" selection, where the population without the new allele are incapable of reproducing fast enough to maintain the population. "Soft" selection, where the population is not in danger, but those with the new allele outcompete the rest, or drift, allow multiple alleles to be fixed in parallel. The absolute time for any one allele to achieve fixation may be higher but the number that can be fixed over a given period is also higher than Haldane's dilemma implies.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Thats why I said "IF".
PS: I referring to message 5 Edited by CoolBeans, : No reason given.
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PaulK Member Posts: 17825 Joined: Member Rating: 2.2 |
i should add to this that the majority of the difference between human and chimpanzee is in "junk" DNA which is not subject to selection. This DNA changes by genetic drift and is not subject to the "dilemma"
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Well 20% is junk DNA so it is a good point.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
Well 20% is junk DNA so it is a good point. Probably much more than that is junk. Even the ENCODE people admitted that only 10-20% of the genome is under selective pressure which would be the preferred criteria for this thread. The other 80% does not appear to have sequence specific function. Either that, or it is invulnerable to deleterious mutations: On the Immortality of Television Sets: Function in the Human Genome According to the Evolution-Free Gospel of ENCODE | Genome Biology and Evolution | Oxford Academic
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PaulK Member Posts: 17825 Joined: Member Rating: 2.2 |
Much, much more than 20% of human DNA is "junk".
According to biochemist Larry Moran, as of 2011 65% of human DNA was known "junk", 8.7% was known not to be, and 26.3% was unknown. So somewhere in the 80-90% range would be far more likely.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
Hmm I will read it later.
----------- A review of ReMine's work would be nice too.
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CoolBeans Member (Idle past 3635 days) Posts: 196 From: Honduras Joined: |
It seems that he wants to redefine the cost of substitution. Or at least clarified it. He cites Dr. Crow as authorities that have reviewed his work. He also argues that neutral mutations do influence too.
Edited by CoolBeans, : No reason given. Edited by CoolBeans, : No reason given.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
Hmm I will read it later. ----------- A review of ReMine's work would be nice too. The important take home message is that Haldane's Dilemma is not a dilemma. He was just wrong. Slightly deleterious mutations can be removed from the population through selection (even through neutral drift), and alleles can be fixed in parallel, not one at a time. Selective sweeps also solve the dilemma. Even in inheritance systems that are the most unforgiving (i.e. asexual reproduction) we still see that there is no dilemma. It is called Muller's Ratchet, an effect where deleterious mutations build up in asexual populations. What scientists did was look at endosymbionts which are bacteria that can only live within host cells and are passed on from one host to the next. They compared the endosymbionts between host species which gives them a known time of divergence which can be used to measure mutation rates and fixation rates. What did they find? "A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed."Background Primary bacterial endosymbionts of insects (p-endosymbionts) are thought to be undergoing the process of Muller's ratchet where they accrue slightly deleterious mutations due to genetic drift in small populations with negligible recombination rates. If this process were to go unchecked over time, theory predicts mutational meltdown and eventual extinction. Although genome degradation is common among p-endosymbionts, we do not observe widespread p-endosymbiont extinction, suggesting that Muller's ratchet may be slowed or even stopped over time. For example, selection may act to slow the effects of Muller's ratchet by removing slightly deleterious mutations before they go to fixation thereby causing a decrease in nucleotide substitutions rates in older p-endosymbiont lineages. Methodology/Principal Findings To determine whether selection is slowing the effects of Muller's ratchet, we determined the age of the Candidatus Riesia/sucking louse assemblage and analyzed the nucleotide substitution rates of several p-endosymbiont lineages that differ in the length of time that they have been associated with their insect hosts. We find that Riesia is the youngest p-endosymbiont known to date, and has been associated with its louse hosts for only 13–25 My. Further, it is the fastest evolving p-endosymbiont with substitution rates of 19–34% per 50 My. When comparing Riesia to other insect p-endosymbionts, we find that nucleotide substitution rates decrease dramatically as the age of endosymbiosis increases. Conclusions/Significance A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed. This countering effect of selection could slow the overall rate of endosymbiont extinction. What happens is that each slightly deleterious mutation adds to those already present until you hit a level where they are selectable. Think of it as the "straw that broke the camel's back". This shows that Haldane was wrong and there is no dilemma.
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