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Author Topic:   Can Genetic Loss Increase Diversity?
Quetzal
Member (Idle past 5873 days)
Posts: 3228
Joined: 01-09-2002


Message 16 of 23 (350756)
09-20-2006 4:46 PM
Reply to: Message 15 by Jazzns
09-20-2006 1:38 PM


Re: Speciation
Correct me if I am wrong, but is not drift driven at least partially by mutation? If the only thing that is happening in drift is allele reshuffling then how can the drifting populations ever be made incompatable?
Not necessarily. The idea here is that frequencies of existing variation within a population can change due to drift of alleles that are generally neutral or even mildly deleterious. Let me see if I can explain it a bit better.
Let’s say we have a population that has two loci: A and B. There are two alleles for each locus: A1 and A2, and B1 and B2. Let’s say the homozygous combination A1A1/B1B1 is “normal” with respect to fitness, but say the occasional A2A2/B2B2 is present but mildly deleterious in the ancestral habitat (or as far as that goes, could be simply different without either negative or positive effects). However, heterozygote combinations/hybrids are invariably deleterious in the ancestral “sub-1” environment. This would tend to keep the frequency of the latter fairly low. Then let’s say a random combination of a bunch of A1A1/B1B1 and A2A2/B2B2 found a colony. IF the A2A2/B2B2 homozygotes are favored in the new environment, then the frequency of the two alleles would change due to the action of natural selection, all other things being equal. Eventually, the “sub-2” population will dominate, and the “sub-one” alleles may eventually disappear from the “sub-2” population. This isn’t speciation, of course (since there’s no real barrier to reproduction with the ancestral population), and doesn’t include drift. Here’s the rub: what if A1 is neutral with respect to fitness on a “sub-2” background? That it’s only when A1 is combined with B1 in a “sub-2” environment that the combination is deleterious? Since A1 is neutral (not under selection), eventually some A2 are going to be replaced by A1 on a relatively random basis - through drift (alternatively, of course, A1 could simply disappear the same way). IF the combination A2A1 is linked to other genes epistatically, then the frequency of those linked genes increases as well. The new genetic composition of the colony through drift may be the cause of incompatibility between the two populations - ancestor and daughter. It isn’t because natural selection is favoring the heterozygote A’s in the “sub-2” population - simply that the ancestral homozygous karyotype is no longer fertile with the “new”, epistatically-driven frequency. This is the ONLY conceivable way for a recombination of existing alleles to create the effect Faith is insisting occurs IN ALL CASES.

This message is a reply to:
 Message 15 by Jazzns, posted 09-20-2006 1:38 PM Jazzns has replied

Replies to this message:
 Message 17 by Jazzns, posted 09-20-2006 7:13 PM Quetzal has replied

  
Jazzns
Member (Idle past 3912 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 17 of 23 (350799)
09-20-2006 7:13 PM
Reply to: Message 16 by Quetzal
09-20-2006 4:46 PM


Re: Speciation
Thanks for the breakdown.
Just to see if I am understanding it correctly, it is because the heterozygous combinations are deleterious in the ancestral population that allows this potential effect of no-mutation-drift to cause speciation in this case?
In the end though, the claim still seems to be that this is the NORM.

Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

This message is a reply to:
 Message 16 by Quetzal, posted 09-20-2006 4:46 PM Quetzal has replied

Replies to this message:
 Message 18 by Quetzal, posted 09-20-2006 8:08 PM Jazzns has not replied
 Message 22 by Quetzal, posted 09-21-2006 8:56 AM Jazzns has not replied

  
Quetzal
Member (Idle past 5873 days)
Posts: 3228
Joined: 01-09-2002


Message 18 of 23 (350814)
09-20-2006 8:08 PM
Reply to: Message 17 by Jazzns
09-20-2006 7:13 PM


Re: Speciation
You got it.
In the end though, the claim still seems to be that this is the NORM.
And this is in fact the issue. The case for this type of speciation is purely hypothetical - to the best of my knowledge, there has been no unequivocal observation showing that speciation by genetic drift is anything but theoretical. There have been some tantalizing hints, especially in insect studies, but no "for sure" example. So not only is this type of speciation not "the norm", but may not even really exist.

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Faith 
Suspended Member (Idle past 1445 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 19 of 23 (350857)
09-20-2006 10:24 PM
Reply to: Message 9 by mick
09-20-2006 6:56 AM


Re: dog breeding
Mick,
You have to write that a lot more clearly. I can't follow that. I don't know what a microsatellite is. You haven't proved a thing until you make it comprehensible. I haven't mentioned heterozygosity so what does it prove to emphasize that anyway? I've talked about an overall trend to reduced genetic diversity. Make your point please.
I hope I'll have more time eventually to think through stuff like this.
Also, I have no idea whether a given breed would have lower anything than a wild breed. I haven't suggested such a thing. I've merely said that the process of domestic breeeding DEMONSTRATES THE PRINCIPLE I'M TALKING ABOUT.
By the way I posted links that said what I'm saying. Sorry I'll have to wait to try to track them down later.
Edited by Faith, : No reason given.

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Faith 
Suspended Member (Idle past 1445 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 20 of 23 (350859)
09-20-2006 10:30 PM
Reply to: Message 10 by Jazzns
09-20-2006 10:12 AM


Re: Answer to Parasomnium
This is exactly what I am claiming has not been established. There has been no connection or valid argument to suggest that NEW TRAITS can arise from recombination alone.
OK I"m going to stop posting to this thread until my computer is in better shape but I posted stuff demonstrating this on the other thread.
Breeders have traditionally bred for observed traits. The more they select for those traits the more the traits get defined in their breed. The traits ARE ALREADY THERE in the dog population. That means the ALLELES for those traits are already there, so they are selecting alleles. They are carefully eliminating other alleles. You are assumign somewhere in there that mutation has made those alleles. THAT is what there is no evidence for. All we KNOW, actually KNOW, is that those traits were THERE in the population and their alleles were there.

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 Message 21 by Woodsy, posted 09-21-2006 8:02 AM Faith has not replied
 Message 23 by Parasomnium, posted 09-21-2006 9:59 AM Faith has not replied

  
Woodsy
Member (Idle past 3374 days)
Posts: 301
From: Burlington, Canada
Joined: 08-30-2006


Message 21 of 23 (350945)
09-21-2006 8:02 AM
Reply to: Message 20 by Faith
09-20-2006 10:30 PM


Re: Answer to Parasomnium
How do you know that they are already there? I gather that breeders sometimes propagate what are known as "sports"; that is, animals with unexpected new traits. Why would you assume that the new traits are somehow already present? Your insistance that any new feature is already encoded when it appears seems very suspicious to me.

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 Message 20 by Faith, posted 09-20-2006 10:30 PM Faith has not replied

  
Quetzal
Member (Idle past 5873 days)
Posts: 3228
Joined: 01-09-2002


Message 22 of 23 (350953)
09-21-2006 8:56 AM
Reply to: Message 17 by Jazzns
09-20-2006 7:13 PM


Re: Speciation
Hi Jazz,
Just to see if I am understanding it correctly, it is because the heterozygous combinations are deleterious in the ancestral population that allows this potential effect of no-mutation-drift to cause speciation in this case?
I just realized that this may require some clarification to make sure that all the bases are covered. In addition to what you wrote, the following are also necessary for speciation by genetic drift (at least using the hypothetical example I gave):
1. The A1 allele must be neutral with regards to fitness in the new (sub-2) environment. When the A1 is linked to a B2 backbone, it is not disvafored. During the time when the B1 alleles are being eliminated, the A1 must replace an A2 allele.
2. The A1 allele must reach fixation in the sub-2 population. This is where the random walk of genetic drift comes in - the allele could just as easily be eliminated through this means.
3. The A2A1 heterozygote must be linked to other suites of genes. As and if A1 increases in frequency, the frequency of these other genes also increases willy-nilly.
When these four (yours and the three I noted) conditions are met, the genetic composition of the colony MAY have changed enough to create a reproductive barrier with the ancestral population. And again, it may not.
Hope this clarifies, rather than obscures.
Edited by Quetzal, : No reason given.

This message is a reply to:
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Parasomnium
Member
Posts: 2224
Joined: 07-15-2003


Message 23 of 23 (350976)
09-21-2006 9:59 AM
Reply to: Message 20 by Faith
09-20-2006 10:30 PM


Re: Answer to Parasomnium
All we KNOW, actually KNOW, is that those traits were THERE in the population and their alleles were there.
Wrong. We don't KNOW that, you are just assuming that. You are doing exactly what you are accusing evolutionists of doing, i.e. making unwarranted assumptions. In the days that there were no bulldogs and no one had ever seen a dog with as short a muzzle as that of a bulldog, there was no way anyone could know that there existed an allele (or alleles) for such an appearance.
There are two reasons why this should be so. First, genetic science had not yet advanced to the level of today, meaning that no one knew even what an allele was, let alone that they knew whether a particular allele existed or not. Second, before there were bulldogs, the allele(s) for the form of its muzzle really did not exist, it's as simple as that.
You simply cannot know that such an allele has always existed, because it is impossible to know it, and because it hasn't. In your own words: "it's all assumption".
On the other hand, we do know that mutations occur, we can see them happening all the time, we can even make them happen, and we have a record of them happening throughout life's history. It is only a logical conclusion that they must play a role in how evolutionary history unfolds. True, in the end, the role of mutations is an assumption, born from logical inference, but it's testable assumption, and all tests to date have vindicated it.

"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.
Did you know that most of the time your computer is doing nothing? What if you could make it do something really useful? Like helping scientists understand diseases? Your computer could even be instrumental in finding a cure for HIV/AIDS. Wouldn't that be something? If you agree, then join World Community Grid now and download a simple, free tool that lets you and your computer do your share in helping humanity. After all, you are part of it, so why not take part in it?

This message is a reply to:
 Message 20 by Faith, posted 09-20-2006 10:30 PM Faith has not replied

  
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