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Author Topic:   Evolution Requires Reduction in Genetic Diversity
RAZD
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From: the other end of the sidewalk
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Message 961 of 1034 (759983)
06-16-2015 1:27 PM
Reply to: Message 947 by jar
06-16-2015 9:15 AM


Re: let them drink milk
Would lactose tolerance be a clear example of a mutation that increased genetic diversity and can be shown to actually be beneficial?

Would sickle cell anemia be a clear example of a mutation that increased genetic diversity and can be shown to actually be beneficial?

Indeed it would show diversity. The question to faith was not that there were no changes in the different populations, but whether it was insufficient to cause speciation and would that mean that we have used up the available diversity to enable speciation -- her argument applied to humans.

There was no apparent pressure to cause speciation that I can see at this time.

Enjoy


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NosyNed
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Posts: 8800
From: Canada
Joined: 04-04-2003
Member Rating: 10.0


Message 962 of 1034 (760009)
06-16-2015 5:30 PM
Reply to: Message 954 by Faith
06-16-2015 10:33 AM


Mutations
Where are your otherwise so plentiful mutations then?

You, yourself, have somewhere around 100 mutations that make you different from your parents or any recombination of their alleles. They are very plentiful.


This message is a reply to:
 Message 954 by Faith, posted 06-16-2015 10:33 AM Faith has responded

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Faith
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Posts: 26449
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 963 of 1034 (760012)
06-16-2015 6:44 PM
Reply to: Message 962 by NosyNed
06-16-2015 5:30 PM


Re: Mutations
All those mutations are like a ticking time bomb, it seems to me, nothing likely to contribute to anyone's health.
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Faith
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Posts: 26449
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 964 of 1034 (760098)
06-17-2015 3:47 PM
Reply to: Message 943 by herebedragons
06-15-2015 10:24 PM


Re: Back to HBD's Chart: Trying New Wording
If I use my own words I think I get it better, but you can tell me:

MUTATION:
Adds an allele, so adds diversity to pop B = INCREASE WITHIN B
Population A doesn't change, so there is now more of a difference between A and B than there was before = INCREASE IN DIFFERENCE BETWEEN the two populations
Does not affect all loci

MIGRATION: (corrected by Admin and PaulK below)
Adds to one by subtracting from the other = INCREASE WITHIN B, (decrease within A for some reason not mentioned)
One gains, one loses, so they are now LESS different than they were before= DECREASE IN DIFFERENCE BETWEEN A and B
Yes affects all Loci

DRIFT:
Subtracts from B, A doesn't change= DECREASE WITHIN B
B is now more different from A than before = INCREASE IN DIFFERENCE BETWEEN A and B
Yes affects all Loci

SELECTION: My first take:
Selection replaces one trait with another or its allele with another, so it subtracts diversity from B = DECREASE IN DIVERSITY WITHIN B
A doesn't change so there is an INCREASE IN THE DIFFERENCE BETWEEN A and B

But it's apparently more complicated than that, as you say, which I'll copy here and come back to it later:

Fourth, Selection:
... selection would bring about both INCREASE AND DECREASE in genetic diversity

Increase OR decrease. Selection is kind of a difficult one. It will probably take more explaining that I have time for now, but I will at least explain the chart.
Some alleles would tend to be favored and would increase in frequency, some alleles would be less favorable and would tend to decrease in frequency. As selection continues to act on the population the tendency would be that diversity within that population will DECREASE as the population moves towards an optimum fitness. However, there are situations where diversity can INCREASE such as with heterozygote advantage (where the heterozygote is more fit that either homozygote).

If different selection pressures are operating on each population we would expect diversity between the two populations to INCREASE as in each population different alleles or combinations are being favored. However, if two populations are already slightly diverse and the same selection pressure begins to act on both populations, then they will become more similar, or diversity will DECREASE.

It does not affect all loci because, in general, only loci that are being selected for or against will be affected.

Like I said, selection is not quite as straight forward as the others and is a bit more difficult to grasp

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


This message is a reply to:
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Replies to this message:
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Admin
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Posts: 12533
From: EvC Forum
Joined: 06-14-2002
Member Rating: 1.8


Message 965 of 1034 (760103)
06-17-2015 4:13 PM
Reply to: Message 964 by Faith
06-17-2015 3:47 PM


Moderator Clarification
Faith writes:

MIGRATION:
Adds to one by subtracting from the other = INCREASE WITHIN B, (decrease within A for some reason not mentioned)

It's not impossible for there to be a decrease in the diversity of A, but it's very unlikely. Consider just one loci for populations A and B. Population A has alleles X, Y and Z for this loci, while population B has only Y and Z. Now an individual with allele X migrates from A to B, which adds allele X to population B and increases its diversity. But the migration of this single individual from population A to B does not remove the X allele from population A. There are still plenty of individuals in population A with allele X.

In order for A to lose diversity, all individuals with allele X would have to migrate away. That's very unlikely.


--Percy
EvC Forum Director

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PaulK
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Posts: 13228
Joined: 01-10-2003
Member Rating: 1.9


Message 966 of 1034 (760104)
06-17-2015 4:15 PM
Reply to: Message 964 by Faith
06-17-2015 3:47 PM


Re: Back to HBD's Chart: Trying New Wording
quote:

MIGRATION:
Adds to one by subtracting from the other = INCREASE WITHIN B, (decrease within A for some reason not mentioned)
One gains, one loses, so they are now LESS different than they were before= DECREASE IN DIFFERNCE BETWEEN A and B
Yes affects all Loci

A little more thought is needed here:

Migration will not typically subtract alleles from A.

To add alleles to B only requires at least one of the migrants has an allele not found in population B. And adding an allele to B that was previously found in A but not B will decrease the difference between the populations.

To subtract alleles from A every individual with that allele must be among the migrants. That's not impossible but I wouldn't expect it to be common. And this would NOT decrease the difference between the populations - the allele would still only be found in one population.

So, the typical situation - the one envisioned in the table - is that migration will add alleles to B previously only found in A, but that A will still include these alleles. This increases the diversity within B but decreases the difference between the two populations.


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Faith
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Posts: 26449
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 967 of 1034 (760107)
06-17-2015 4:21 PM


Admin and PaulK
OK I get it, thanks.
    
NoNukes
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Posts: 9998
From: Central NC USA
Joined: 08-13-2010
Member Rating: 2.2


Message 968 of 1034 (760108)
06-17-2015 4:22 PM
Reply to: Message 964 by Faith
06-17-2015 3:47 PM


Re: Back to HBD's Chart: Trying New Wording
DRIFT:
Subtracts from B, A doesn't change

The statement above makes no sense whatsoever.

Selection replaces one trait with another or its allele with another

Nope. Not even close to a good definition of selection or its results. Yes there is an attendant reduction in diversity.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

History will have to record that the greatest tragedy of this period of social transition was not the strident clamor of the bad people, but the appalling silence of the good people. Martin Luther King

If there are no stupid questions, then what kind of questions do stupid people ask? Do they get smart just in time to ask questions? Scott Adams


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PaulK
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Posts: 13228
Joined: 01-10-2003
Member Rating: 1.9


(2)
Message 969 of 1034 (760110)
06-17-2015 5:16 PM
Reply to: Message 964 by Faith
06-17-2015 3:47 PM


Re: Back to HBD's Chart: Trying New Wording
For drift, I will just point out that in reality drift will affect A.

quote:

SELECTION: My first take:
Selection replaces one trait with another or its allele with another, so it subtracts diversity from B = DECREASE IN DIVERSITY WITHIN B
A doesn't change so there is an INCREASE IN THE DIFFERENCE BETWEEN A and B

Selection can be positive or negative. Alleles that add to fitness will become more common, those that subtract from it will become less common. In either case it will tend to eliminate alleles. That's how selection reduces diversity within a population.

As I pointed out in the discussion with jar, sickle-cell is an unusual case where selection maintains diversity. This is an example of "heterozygote advantage" where - according the the chart - selection increases diversity. Having one sickle-cell allele is better (in the presence of malaria) than having none or (worse) two. As a consequence selection is positive when the allele is rare and negative when it is common. (It requires some thought but it does work out)

The difference between the populations is also listed as increase/decrease, but that is easier to understand. If alleles present in A and remaining in A are removed from B this increases the difference. If alleles not in A are eliminated from B (e.g. deleterious mutations) then it will decrease the difference.

Edited by PaulK, : No reason given.


This message is a reply to:
 Message 964 by Faith, posted 06-17-2015 3:47 PM Faith has responded

Replies to this message:
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NoNukes
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Posts: 9998
From: Central NC USA
Joined: 08-13-2010
Member Rating: 2.2


Message 970 of 1034 (760117)
06-17-2015 7:10 PM
Reply to: Message 969 by PaulK
06-17-2015 5:16 PM


Re: Back to HBD's Chart: Trying New Wording
For drift, I will just point out that in reality drift will affect A.

Yes. If we are eliminating all other effects, then of course drift must happen in all populations.

And perhaps there is a tendency in smaller populations that rare alleles are more likely to be lost or that the allele frequencies will vary more over time than in a large population, just because of the way statistics in large and not so large numbers works. But there is no way to predict how long it would take to expunge any particular trait absent selection.

Decrease in diversity over time within a population but over an unpredictable time scale, unpredictable affect on the difference between two populations with an increase being most likely?

Edited by NoNukes, : No reason given.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)

History will have to record that the greatest tragedy of this period of social transition was not the strident clamor of the bad people, but the appalling silence of the good people. Martin Luther King

If there are no stupid questions, then what kind of questions do stupid people ask? Do they get smart just in time to ask questions? Scott Adams


This message is a reply to:
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Replies to this message:
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PaulK
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Posts: 13228
Joined: 01-10-2003
Member Rating: 1.9


Message 971 of 1034 (760135)
06-18-2015 1:06 AM
Reply to: Message 970 by NoNukes
06-17-2015 7:10 PM


Re: Back to HBD's Chart: Trying New Wording
Because drift is random it has more extreme effects in small populations.

quote:

Decrease in diversity over time within a population but over an unpredictable time scale, unpredictable affect on the difference between two populations with an increase being most likely?

Divergence is almost inevitable. To avoid it the same alleles would have to be lost to drift in both populations. While that is possible in a random process it's hardly likely.


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Faith
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Posts: 26449
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 972 of 1034 (760149)
06-18-2015 6:45 AM
Reply to: Message 969 by PaulK
06-17-2015 5:16 PM


Re: Back to HBD's Chart: Trying New Wording
For drift, I will just point out that in reality drift will affect A

For some reason the effect on only one population is considered on the chart. I think HBD mentioned this but I'll wait until he responds to all this.

Selection can be positive or negative. Alleles that add to fitness will become more common, those that subtract from it will become less common. In either case it will tend to eliminate alleles. That's how selection reduces diversity within a population.

Which I take into account whenever selection comes up in my argument. But HBD's chart has Increase/Decrease and Increase/Decrease so he's going to have to explain some more.


This message is a reply to:
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Replies to this message:
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PaulK
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Posts: 13228
Joined: 01-10-2003
Member Rating: 1.9


(1)
Message 973 of 1034 (760150)
06-18-2015 6:55 AM
Reply to: Message 972 by Faith
06-18-2015 6:45 AM


Re: Back to HBD's Chart: Trying New Wording
quote:

Which I take into account whenever selection comes up in my argument. But HBD's chart has Increase/Decrease and Increase/Decrease so he's going to have to explain some more.

He already has Message 931. My post has a simpler version of the explanation. I don't know why you didn't respond to that.


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herebedragons
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Posts: 1413
From: Michigan
Joined: 11-22-2009
Member Rating: 2.2


Message 974 of 1034 (760235)
06-18-2015 10:47 PM
Reply to: Message 964 by Faith
06-17-2015 3:47 PM


Re: Back to HBD's Chart: Trying New Wording
Sorry, I've had a lot going in the last week. I thought things were going to slow down for me this summer, but I can't seem to catch a break

If I use my own words I think I get it better, but you can tell me:

I think you pretty much get the gist of it. I want to go back and explain a little more about drift, particularly the idea of sampling error.

SELECTION: My first take:
Selection replaces one trait with another or its allele with another, so it subtracts diversity from B = DECREASE IN DIVERSITY WITHIN B
A doesn't change so there is an INCREASE IN THE DIFFERENCE BETWEEN A and B

But it's apparently more complicated than that, as you say, which I'll copy here and come back to it later:

Most of the time this is how selection works. There are exceptions though that can reverse these trends, that is why the chart says "Increase/Decrease." But those exceptions are generally rare and the net effect is that most of the time the two populations will become increasingly different.

You asked somewhere what all this has to do with your argument, and I guess I will just say that what I hope to be able to do is to show how populations (and their diversity) are currently studied and what those studies tell us about diversity.

HBD


Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca

"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.

Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.


This message is a reply to:
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herebedragons
Member
Posts: 1413
From: Michigan
Joined: 11-22-2009
Member Rating: 2.2


Message 975 of 1034 (760236)
06-18-2015 11:04 PM
Reply to: Message 972 by Faith
06-18-2015 6:45 AM


Re: Back to HBD's Chart: Trying New Wording
For some reason the effect on only one population is considered on the chart.

You could add another column for Population A, but it would be the same as for population B. Perhaps the assumption we could make here is that A is a larger population so the effects would not be as noticeable as they are in the smaller, population B.

It seems the only factor where it is not clear to you that A and B would be the same change in diversity is migration, it seems as if one population increases the other must decrease. But I think Percy and PaulK have cleared that up. ALL the individuals with a particular allele would have to leave a population in order to decrease the diversity of that population, whereas only ONE individual with a new allele would have to migrate into population in order to increase the diversity of that population. It should be clear what the TREND would be.

But HBD's chart has Increase/Decrease and Increase/Decrease so he's going to have to explain some more.

Some examples have already been given of how selection can increase diversity in a population. These situations are rare (but very interesting) and for the most part, selection reduces diversity within a population and increase diversity between populations.

HBD


Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca

"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.

Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.


This message is a reply to:
 Message 972 by Faith, posted 06-18-2015 6:45 AM Faith has not yet responded

  
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