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Rule -> RE: Jew Hitler a Rothschild? ?? huh? (1/21/2010 3:51:46 AM)
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quote:
ORIGINAL: DomKen
Mutations occur at the same frequency but (due to the small number of mutations that aren't completely neutral: many third 'letters' in each codon can be changed and still produce the same amino acid in the same spot in the protein as well as many amino acid substitions being completely neutral) the mutations we notice and care about are very small in number.
I have edited your above quote a bit; the sentence was long and then it may happen that the thought is not expressed as accurately as intended. I think this is what you meant to say? If so, I agree: significant mutations are rare and if recessive - as the huge majority initially are until further mutations occur in that or other genes that confer dominance (to primarily beneficial or neutral mutations) - many will hardly be noticed.
quote:
ORIGINAL: DomKen
So the frequency of any allele may differ quite significantly between larger and smaller populations. Until you understand and accept that fact you won't ever understand why small reproductively isolated populations have more frequent instances of specific genetic diseases.
I do not understand it. This your conclusion does not follow from your previous quote.
We know that mutations occur all the time, not only in gametes, but also in non-gamete cells, in the latter case sometimes resulting in cancer (though I suspect most cancers are caused by viruses).
It is wrong to focus on a single deleterious mutation in one specific gene.
You have already agreed that new mutations occur at the same frequency. We are talking about deleterious mutations, specifically - for simplification of the model - about lethal recessive mutations. If we have a small population of ten and a large population of one hundred and each generation is the same size, then if in the small population in each generation is born one individual with a lethal recessive, then in the large population in each generation ten individuals are born with a lethal recessive, not so?
So in the eleventh generation in the small population there are about ten lethal recessives and in the large population there are about one hundred lethal recessives, purely from accumulating new deleterious mutations (not necessarily in all individuals; also, genetic drift will already have been active, as ten new generations is a lot).
You do agree that without an efficient means to remove deleterious (lethal) recessive mutations from the gene pools, that such mutations will accumulate in the gene pool, don't you? Given time, identical new mutations will occur.
In small (island) populations genetic drift will either rapidly throw out new mutations or have them occupy every position in the gene pool, whereas in larger populations this genetic drift algorithm is not as vehement: the mutations can initially be thrown out as rapidly, but it takes far longer for them to occupy every available position in the gene pool (that would be half the gene pool if it concerns lethal recessives). So yes, due to genetic drift one single lethal mutation may occur in high frequency in small populations and in low frequencies in larger populations - and present proportionately in the phenotype. (The plus side is that the same will happen to beneficial mutations.) On the other hand one single mutation may disappear from a small population yet still be present in a large population.
Unlimited genetic drift may cause the entire population to be affected for a very long time. To limit the spread of the deleterious allele and to shorten the time it is in a population, both due to genetic drift, the population size must be reduced as much as possible: to siblings and first cousins. The much stronger benefit of which is that alleles in homozygous individuals will be removed from the gene pool.
Genetic drift, though, does not change the combined frequency of lethal recessive alleles in a population, it is the same in both small and large populations.
Let me return to the eleventh generation and in an extreme model assume that the lethal recessive mutations from the second generation are heterozygously present in all ten individuals of the small population. Thus to the couples will be born ten children, 2.5 of which will die, five of which will be heterozygous and 2.5 of which will be without the deleterious allele. The frequency of the deleterious allele in the gene pool is reduced from fifty per cent to twenty-five per cent. The population will have reduced from 10 to 7.5.
In the larger population the same occurs: for simplicity I assume that each individual is heterozygous for one of the initial ten lethal recessives. Each (assuming that the alleles are equally distributed among the sexes) has a 5/50 = 1/10 change of meeting a partner with the same allele. Of one hundred children born, 2.5 of which will die, 2.5 of which will be without any deleterious allele, ninety-five of which will be heterozygous for one or more of the lethal recessives. The combined frequency of the deleterious alleles in the gene pool is reduced from fifty per cent to forty-five per cent. The population will have reduced from 100 to 97.5. So the presentation of homozygous lethal recessive is at a ten times lower frequency than in the small population.
I also note that the small population goes extinct at a much faster rate.
Are my calculations correct? Is this the phenomenon you were talking about: relatively more phenotypical presentation in small than in large populations?
I will have to cogitate on this, as you may have a point.
quote:
ORIGINAL: DomKen
No if you go back and look I'm responding to your handwave where you ignored my example involving a large and small population. You tried to claim that in two isolated populations of the same species a mutation would be present at the same frequency which is simply wrong and I've now pointed it out to you several times. For a supergenius you're pretty damn slow.
I am a low IQ supergenius, as I have said in other, earlier threads. There are plenty of geniuses that think a lot faster on their feet than I do - but usually they cannot do what I do.
quote:
ORIGINAL: DomKen
So close and yet so far. In actuality the mutation events are rare and the genome is huge. Even when a mutation does occur the carrier must pass it on to offspring or it may as well never happened. So while a mutation may occur in more than on individual it is very rare and when dealing with small reproductively isolated groups with a high prevalence of otherwise rare genetic diseases it is safe to assume that it is either the result of a founder being a carrier or that a mutation occurred in the population after isolation began unless there is some strong evidence to the contrary.
There is one fly in the ointment: the population of Muslims is huge. Nevertheless they are highly inbred populations with about an equal frequency of inherited diseases presenting as occur among Jews (and presumably among Amish and Mennonites and Anabaptists). Care to explain why the huge Muslim population is strongly inbreeding from a population genetics point of view?
quote:
ORIGINAL: DomKen
To make clear how unlikely it is that the exact same mutation occurs and gets into the population I point you to this study of the origins of the sickle cell mutation which indicates that the mutation has occurred and survived only 3 times in the last 6000 or so generations.
I will study your link at a later time.
quote:
ORIGINAL: DomKen
The founder effect is part of it but it is clearly not all. mutations occur post isolation just as they did before the populations split and obviously every allele in the larger population will not be present, or will not survive, in the newly isolated population.
Founder effect and genetic drift are two different phenomena.
This is getting interesting. I have to go now for a couple of days. I will return on Saturday or Sunday.
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