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Author Topic:   A Creationist's view of Natural Limitation to Evolutionary Processes (2/14/05)
DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 44 of 218 (185897)
02-16-2005 2:39 PM
Reply to: Message 5 by Faith
02-14-2005 5:37 PM


Re: Considering rapid rate of mutation
As for a very high rate of beneficial variations changing the picture here, assuming that such occur for the sake of argument as you propose, which I believe is highly doubtful, even if huge quantities of new adaptive alleles were to enter the population [at least as problematic a possibility as the idea of God's intervention I would think], natural selection and the other evolutionary processes are going inexorably to operate in the direction of decreasing variability among them.
The rates of mutation don't need to be high in order to maintain variation because much of variation is protected from selection. For traits that are affected by genes at many different loci, low mutation rates can maintain a populations variability. Many different genotypes generate intermediate phenotypes that are favored by stabilizing selection. If the individuals within a population are all just as likely to survive and reproduce, then a lot of variation is protected from selection. When a large number of loci affect a single trait, only a small fraction of the genetic variability present in the population is expessed phenotypically. Selection removes variation from the population very slowly, if this happens. Recombination and reshuffling will expose these hidden variation to natural selection in later generations. Because of this protection from selection, a low mutation rate can maintain variation despite natural selections tendency to decrease variation.
Hidden variation is always present in continuously varying traits.
This is the reason that we can get different forms of species via artificial selection. A chihuahua(sp?), which is smaller than the smallest wolf, has been and could be selected for by humans over a very short period of time because within the genes of wolves, there must have been these hidden variations!

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DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 45 of 218 (185899)
02-16-2005 2:57 PM
Reply to: Message 6 by Faith
02-14-2005 9:28 PM


Re: Novel mutations?
They seem to know how many different genes are involved in the production of different colors and patterns of coats in dog breeds for instance, and how these can combine to produce desired results in offspring. This is all genetic business as usual, involving no novel mutations. Novel mutations would be unpredictable in any case, but the business of breeders is prediction.
(My bold)
But the fact is that novel mutations DO take place and breeders do USE them in breeding. There are different breeds of domestic cats which came about due to some novel mutation.
For example:
quote:
On a sunny day in June 1981 in Lakewood, California, a longhair silky black female kitten with unusual ears wandered up to the doorstep of Joe and Grace Ruga. Joe scrutinized the situation and determined that the most effective solution to this stray kitten problem was to ask Grace not to feed the kitten. Grace, not abiding by her husband's wishes but listening to her heart instead, left a bowl of food on the porch. The affectionate black kitten quickly worked her way into the Ruga's hearts (especially Joe's) and they named her Shulamith, which means "black but comely". Such are the beginnings of the American Curl as it is known today. True American Curls must trace their pedigree back to Shulamith, the foundation female.
In December 1981, Shulamith delivered her first litter of kittens. Out of four kittens, two had the same curly ears as Shulamith. A geneticist was contacted to study this phenomenon and he confirmed that this unusual ear was a genetic trait and was inherited in every case, causing it to be labeled a dominant gene, with no deformities attached to it. Referred to as a spontaneous mutation, the gene that causes the ear to curl appeared to be following a single dominant pattern.
From: Cat Fanciers Website

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 Message 6 by Faith, posted 02-14-2005 9:28 PM Faith has not replied

DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 52 of 218 (185962)
02-16-2005 5:40 PM
Reply to: Message 13 by Faith
02-15-2005 8:39 AM


Re: Considering rapid rate of mutation
The processes of variation (called "speciation" by evolutionists) proceed by selecting out portions of the built-in potential for expression in the phenotype. The process ALWAYS involves reduction of the frequency of alleles and of genetic variability because for new traits to come to the fore new allelic combinations are required and you don't get these unless other allelic expressions are somehow suppressed -- or unfortunately in some cases actually killed.
The process of natural selection works on the phenotypes. This can cause a reduction in variation but you mustn't forget that there is still hidden variation within the genotype which can continue on in later generations and not be expressed.

This message is a reply to:
 Message 13 by Faith, posted 02-15-2005 8:39 AM Faith has replied

Replies to this message:
 Message 63 by Faith, posted 02-16-2005 10:54 PM DBlevins has replied

DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 54 of 218 (185982)
02-16-2005 6:48 PM
Reply to: Message 35 by Faith
02-16-2005 7:47 AM


Re: Mutation appears to be everything
Yes, your bacterium. But still in my mind are the examples from the PBS program that called the process of selection of the poisonous newt and the antibiotic-resistant tuberculosis "mutation" while nevertheless ILLUSTRATING the process by diagrams showing that the adaptive trait was present in the beginning of the process. Surely that is not mutation, that is simply an already-present allelic variant. And such a case makes the whole question of mutation very iffy.
How do you think that that adaptive trait came about in the first place? This, I think, is a fundemental problem that you are falling under. Mutation had to have happened at one time or another. This mutation may already have been present in the population but not expressed, until some selective pressure made it beneficial to HAVE that mutation. How do you think you get variations in allele's??

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 Message 35 by Faith, posted 02-16-2005 7:47 AM Faith has replied

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DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 56 of 218 (185986)
02-16-2005 7:00 PM
Reply to: Message 42 by sfs
02-16-2005 12:20 PM


Re: Mutation appears to be everything
Isn't the Hardy-Weinberg Equilibrium equation often used as an indicator that evolution is happening? You can compare allelic frequencies from the equation to actual allelic frequencies in the population to show that/if evolution is happening.

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DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 57 of 218 (185991)
02-16-2005 7:28 PM
Reply to: Message 48 by Faith
02-16-2005 3:36 PM


Re: evolution does not proceed solely by drastic events
Fascinating. So even at the extremes of least genetic variability variation can occur. This and the bacterium example do raise questions about what variation is. The probabilities of anything nonlethal occurring through random "accidents" just "seem" astronomical to my untutored mind. I can't think they are accidents but are obeying some law. It just boggles the mind that an "accident" such as mutation is said to be, can have such a pinpoint nonlethal effect. Deleterious effects, of course, are easy to understand as the product of accidental changes.
Codons can often have a change in the last base without affecting the amino acid it codes for. There are 20 amino acids in biological systems and DNA has 4 base pairs arranged in complementary pairs. That gives us, what, 64 different combinations for the codons. As you can see, those 64 different combinations code for 20 amino acids. As an example: GCT, GCC, GCA all code for alanine. A point mutation can affect the last base of the codon and this would essentially be a neutral mutation. It wouldn't change the code for the amino acid.
Now, if you look at which parts of the DNA strand actually used to code for the proteins produced you would see that often there is much of the strand that is no longer used or codes for nothing. Any change to this portion of the code, via point mutation, would again be neutral. In fact, often mRNA is "snipped" of portions of its chain before it is sent out of the nucleus to be read by the tRNA. (Obviously it is more complicated than this but I hope you get the picture.) That snipped portion might have had a mutation but is ignored because it doesn't pass through.
So you can see that DNA has such redundancies to it, that mutations (specifically point mutations), may not even affect the survival of the organism.

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DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 58 of 218 (185996)
02-16-2005 7:51 PM
Reply to: Message 53 by pink sasquatch
02-16-2005 6:16 PM


Re: selection & mutation - which is faster?
Off the top of my head - hemaglobin allelic diversity is maintained by selective forces. If an individual is homozygous wild-type, they are susceptible to malaria (the selective force); if they are homozygous for the sickle-cell allele, they have anemia. Thus the allelic diversity of having two hemaglobin alleles is maintained in the population, because heterozygous individuals are positively selected for.
There it is - an example of selection maintaining diversity.
Which explains why this mutation is NOT selected against even though having homozygous allele's for sicke-cell is VERY deleterious. I don't think they even live to reproductive age, correct? Having this allele in populations exposed to malaria carrying mosquitos is a positive thing. If you're heterogenous for this trait, you have some resistance to the disease and are able to pass YOUR gene to your offspring. You have a reproductive advantage over the homozygous normal carrying individual in THAT environment.
(I hope you don't mind me adding my comments here. Just hoping he reads through the posts and isn't selective I guess.)
Which reminds me. The change in the gene is a point mutation. IT can be deleterious when you are homozygous for the trait, but heterozygous individuals have a reproductive advantage.

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DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 106 of 218 (186256)
02-17-2005 2:40 PM
Reply to: Message 63 by Faith
02-16-2005 10:54 PM


Re: Considering rapid rate of mutation
Not "can" cause a reduction, but natural selection ALWAYS causes a reduction in variation by selecting some types at the expense of others.
and
None of these processes increase variability to say the least, but an increase in variability would seem to me to be THE engine to drive "macroevolution" if it is really possible.
Natural selection does NOT ALWAYS cause a reduction in variation because hidden variation is ALWAYS present in continuously varrying traits. Natural selection can INCREASE variation. How about an example of how this can come about, eh?
Suppose you have an environment that favors larger beaks in birds. We'll let + equal the gene for large beaks and - as the gene for small beaks. Because deeper beaks is determined by genes at many loci, a population of even large beaked birds + have some small beak genes -. Now when the birds with the smallest beaks die, alleles for the small beaks are removed from the breeding popuation. This may increase the frequency of the + gene at every loci, but because even the larger beaked birds have some - alleles, variation still remains. Reproduction shuffles these genes within the population and because + genes are more common, individuals in future generations will have more + alleles. Because the more + genes you have the deeper your beak, the population will show a shift to larger beaks, and the new generations biggest beaks will be bigger than the previous generation. If this continues the same thing happens again. The individuals with the biggest beaks will have beaks even larger than the previous generation. As you can see you have MORE variation. This process can even be reversed.
An example I have seen used is an experiment on oil content within seeds. The experiment conducted on corn showed that oil content could be increased, after 80 generations, beyond the initial oil content of 4-6%. The researchers were also able to reverse the process and select for low oil content instead. This showed that selection could INCREASE the initial range of variation.
(From Boyd and Silk, ibid, p. 74 with the citing found in the url below)
Evolution: Online course
And finally, where do you think our domestic dogs have come from? If they come from wolves and we SELECTED traits then of course you should be able to see that we do have MORE dog breeds and MORE variation in this species.
It is hidden variation that is selected FOR in many situations of natural selection...
It is EXPRESSED variation that is selected for. Hidden variation is later expressed through reproduction/recombination.

This message is a reply to:
 Message 63 by Faith, posted 02-16-2005 10:54 PM Faith has replied

Replies to this message:
 Message 108 by Faith, posted 02-17-2005 3:38 PM DBlevins has replied

DBlevins
Member (Idle past 3887 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 111 of 218 (186357)
02-17-2005 7:07 PM
Reply to: Message 108 by Faith
02-17-2005 3:38 PM


Re: Considering rapid rate of mutation
I apologize if I misunderstood what you were saying. It seemed to me that you were talking about variation. Specifically a reduction in variation due to genetic drift/ NS.
I do think I percieve what you are saying and perhaps a misunderstanding about alleles that you might have. In your first post you talked about a reduction in alleles:
Migration out of a population leaves both the remaining populations genetically reduced. This is what happened with Darwin's Galapagos turtles. They are both likely to develop traits peculiar to themselves from their reduced allotment of alleles...
This is infact not the case. There is no genetic reduction, or reduced allotment of alleles, as if they are somehow reduced. Instead there is a shift in the frequency of alleles by selection working on the expressed alleles. This may or may not cause a reduction in the "FREQUENCY" of an allele, but that is because the frequency of a selected allele is increased. So if we see in our finches with small beaks that they are selected against, we still have a population of larger beaked birds that may have the small beak alleles. In the case of a drastic reduction, such as a bottleneck the allele frequency may shift so much that the allele for small beaks doesn't exist in the population, but the number of alleles for that trait are still there, they may all be large beak alleles.
To express this visually, suppose you have a population of birds that vary in beak size according to expressed alleles, as shown below (with - allele for small beaks and + allel for larger beaks). Now remember we are talking about continuouly varrying traits or multiple alleles affect a trait (such as height in humans.)
(numbers in parenthesis show hypothetical population)
(5) (11) (20) (30) (21) (10) (3)
-- -- -- -+ -+ -+ ++
-- -- -+ -+ -+ ++ ++
-- -+ -+ -+ ++ ++ ++
Now if some selection pressure caused the smallest beaked birds to die off you still have - genes in all but the largest beaked birds. There was no "reduction" in the alleles that affect beak size but a reduction in the FREQUENCY of the - allele.
This I think is the misperception you have about some reduction.
As far as there being a reduction in variability. Variability is the "ability" to vary. What is stopping a mutation to act on or change one of the alleles, even if they were all + alleles? If a mutation acts or changes one of these alleles it will remain hidden and reshuffled among the population if it isn't detrimental to the reproduction of the species UNTIL selective forces act in such a way that this NOVEL ALLELE becomes expressed. This novel allele may or may not help the species to survive.
This message has been edited by DBlevins, 02-17-2005 19:09 AM

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