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Author Topic:   Evolution Requires Reduction in Genetic Diversity
PaulK
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Message 948 of 1034 (759933)
06-16-2015 9:20 AM
Reply to: Message 947 by jar
06-16-2015 9:15 AM


Sickle-cell anaemia
Sickle-cell anaemia is a case where selection maintains diversity.

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 Message 947 by jar, posted 06-16-2015 9:15 AM jar has replied

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PaulK
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Posts: 17822
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Member Rating: 2.2


Message 950 of 1034 (759936)
06-16-2015 9:45 AM
Reply to: Message 949 by jar
06-16-2015 9:24 AM


Re: Sickle-cell anaemia
I don't think so. The thing about sickle-cell anaemia is that it is the heterozygous condition that is beneficial (in malarial regions). I haven't heard that said about lactase persistence.

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 Message 949 by jar, posted 06-16-2015 9:24 AM jar has replied

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 Message 951 by jar, posted 06-16-2015 9:53 AM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 952 of 1034 (759939)
06-16-2015 9:59 AM
Reply to: Message 951 by jar
06-16-2015 9:53 AM


Re: Sickle-cell anaemia
I think you miss the point. Because the heterozygous condition for sickle-cell is advantageous and the homozygous state is disadvantageous, selection acts to keep a balance. Is there a similar disadvantage to lactase persistence alleles ?

This message is a reply to:
 Message 951 by jar, posted 06-16-2015 9:53 AM jar has replied

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PaulK
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Posts: 17822
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Member Rating: 2.2


Message 955 of 1034 (759943)
06-16-2015 10:41 AM
Reply to: Message 953 by jar
06-16-2015 10:07 AM


Re: Sickle-cell anaemia
quote:
During periods of famine, yes there would be a distinct advantage and so those who lack the trait would be selected.
Still missing the point. Iin the case of the sickle-cell allele, selection will be positive when it is rare and negative when it is common. Thus selection acts to prevent it from becoming either fixed or lost, hence maintaining diversity.
Unless you can show something similar with lactase persistence it is not the same.

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PaulK
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Message 959 of 1034 (759955)
06-16-2015 11:42 AM
Reply to: Message 954 by Faith
06-16-2015 10:33 AM


More misrepresentation from Faith
quote:
What evidence? The evidence is that mutations accomplish very little of use to any organism. Just consider that all jar and PaulK could come up with in their recent posts are the sickle cell example, which offers a protection against malaria at the cost of sickle sickness and death, wonderful gift of mutation. And that other familiar one, can't think of it right now
To correct Faith, I was not even trying to "come up with" examples of mutation, or even challenging jar to come up with more. I was simply pointing out an interesting an relevant fact about suckle-cell.
And the other mutation that Faith conveniently forgets - lactase persistence - seems to be unambiguously useful...

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PaulK
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Posts: 17822
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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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PaulK
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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 replied

Replies to this message:
 Message 970 by NoNukes, posted 06-17-2015 7:10 PM PaulK has replied
 Message 972 by Faith, posted 06-18-2015 6:45 AM PaulK has replied
 Message 976 by herebedragons, posted 06-18-2015 11:39 PM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


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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PaulK
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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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PaulK
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Posts: 17822
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Message 977 of 1034 (760241)
06-19-2015 3:26 AM
Reply to: Message 976 by herebedragons
06-18-2015 11:39 PM


Re: Back to HBD's Chart: Trying New Wording
Perhaps I have misunderstood the terminology, but it seems to me that heterozygote advantage must describe a case where the heterozygote has an advantage over both homozygotes, which is exactly the situation with sickle-cell in malarial regions. If that is not correct I think the term needs to be carefully explained when introduced because it is not obvious. As I have said, an advantage to the heterozygote over both homozygotes will have the consequence of what you called frequency-dependent selection although I would think that a more general term.
I have thought a little more on the matter and it does seem that in this case diversity measured by the proportion of heterozygotes would increase, although diversity measured by the number of different alleles would not. Although this could also be said for selection in general, it is more marked in cases like this.
Edited by PaulK, : No reason given.

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 Message 976 by herebedragons, posted 06-18-2015 11:39 PM herebedragons has replied

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PaulK
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Posts: 17822
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Message 979 of 1034 (760272)
06-19-2015 11:23 AM
Reply to: Message 978 by herebedragons
06-19-2015 7:35 AM


Re: Back to HBD's Chart: Trying New Wording
quote:
which doesn't fit heterozygote advantage
For cases like sickle-cell where selection maintains a balance between alleles it must be the case. Maybe there are cases where it isn't true, and it may depend on relative fitnesses but I'm pretty sure that it is for sickle-cell.

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


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Message 993 of 1034 (769909)
09-26-2015 1:45 PM


Population Genetics - Faith's errors
Faith:
quote:
So as I was pondering (and praying about) that example I realized that for such an event to have occurred would require many stages of population genetics, and that led me to recognize that population genetics doesn't work that way: first it doesn't make incremental changes from generation to generation: in a condition of reproductive isolation it makes clear DIFFERENT phenotypic variations in many individuals that over many further recombinations can become part of a new look for the entire new population.
The first error is that population genetics does not describe phenotypic changes. It describes how alleles change in frequency.
The second error is that population genetics DOES work incrementally over generations. (Indeed, a generation would be a 'round of population genetics')
The third error is - as usual - to exclude the role of mutation
Apparently prayer is no substitute for making the effort to understand what you are talking about.

Replies to this message:
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 Message 995 by Faith, posted 09-28-2015 12:54 PM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


(1)
Message 997 of 1034 (770037)
09-28-2015 2:25 PM
Reply to: Message 995 by Faith
09-28-2015 12:54 PM


Re: Population Genetics - Faith's errors
quote:
Yes, and the phenotypes that emerge come from the greater frequencies
I'm glad that you accept that you misunderstood what population genetics is actually about.
quote:
Sticking with the one and only example I focus on, that of a reproductively isolated daughter population formed from a relatively small number of individuals, what happens in the first few generations is the emergence of a number of different phenotypes in different individuals due to the new gene frequencies, and after whatever number of generations of inbreeding it takes to mix all the genetic types, the population as a whole acquires a new phenotypic look. Where's the incremental development
Unfortunately you've gone right back to repeating your first error immediately after accepting that it was an error. Population genetics does not describe the phenotypic changes. It describes changes in allele frequency and those changes DO take place incrementally over the generations.
Although to be quite honest I would not be surprised to find some examples of incremental change in dogs if we had a decent record. Declaring that it didn't happen without the records that would let you know if it had is just an unsupported opinion.
quote:
That's because, as I've explained so many times, the source of alleles has nothing to do with the processes that reduce genetic diversity.
That's a typical Faith excuse. You can't make a relevant factor irrelevant just by refusing to talk about it.
quote:
The article is concerned with the problems of breeders and the only real description of natural populations is that very large stable sort of population.
Or to put it another way they are really only interested in pure-bred dogs, the problems faced by breeders of those dogs and what to do about them. It's all short-term stuff, related to small, isolated and heavily inbred populations which are rarely found in nature. With artificial selection tending to make the problems worse.
quote:
That really ought to be pretty good support for what I've been arguing.
It isn't. It's almost completely irrelevant. You'd have to be nuts to think that a heavily artificial, short-term situation (which would be expected to lead to extinction) has much to do with long term evolutionary change in nature.
Edited by PaulK, : Minor clarification

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


(1)
Message 1000 of 1034 (770044)
09-28-2015 3:18 PM
Reply to: Message 999 by Admin
09-28-2015 3:00 PM


Re: Population Genetics - Faith's errors
I'm referring to cases where a sequence of phenotypic changes build on top of each other. It wouldn't be that surprising to find a few short sequences. It doesn't even require mutations. If multiple genes affect a feature select for one until an allele is fixed in the breed. Sometime later select on another and so on.
Maybe comparing a breed derived from another with the "parent" breed might show something of the sort, although obviously it couldn't demonstrate a sequence of more than two steps without getting into the genetics. But I would be very, very surprised if Faith has even made a decent attempt at making comparisons of that sort.

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 1005 of 1034 (770062)
09-29-2015 1:08 AM
Reply to: Message 1002 by Faith
09-28-2015 6:44 PM


Faith's new math
quote:
Change in allele frequency most obviously occurs with the formation of a new isolated population by a relatively small number of individuals.
Change in allele frequency goes on all the time. It's just faster in small populations.
quote:
This is the classic view. I don't know where you are getting yours. Other things may contribute to the same effect of course, but population splits are THE known cause of changes in gene/allele frequencie
NO. This is another of your misunderstandings. Selection and drift cause changes in allele frequencies (although selection can also maintain them). Population splits can increase the rate of drift (because the sub-populations are smaller than the whole). But the real reason they are important is that they eliminate gene flow between the sub-populations allowing them to change relative to each other.
quote:
Mutation merely supplies alleles (according to current ToE anyway), but alleles are what get reduced by the evolutionary processes. Mutation therefore does nothing to prevent reduced genetic diversity.
Only if you believe that 2 - 1 + 1 = 1. Faith's new math.

This message is a reply to:
 Message 1002 by Faith, posted 09-28-2015 6:44 PM Faith has replied

Replies to this message:
 Message 1006 by Faith, posted 09-29-2015 1:21 AM PaulK has replied

  
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