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Author Topic:   Wright et al. on the Process of Mutation
shadow71
Member (Idle past 1870 days)
Posts: 706
From: Joliet, il, USA
Joined: 08-31-2010


Message 106 of 296 (635005)
09-25-2011 3:04 PM
Reply to: Message 105 by Percy
09-24-2011 8:43 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
Wright et al writes: Taken from an earlier Percy message.

The current paradigm of neo-Darwinism as formulated by Weisman (59) rejects any influence of the environment on the direction of variation. However, prolonged nutritional stress results in a general increase in mutation rates; the introduction of environmental effects on specific mutation rates is a reasonable extension of what is known, especially because mechanisms by which starvation can immediately and specifically affect rates of transcription and mutation are consistent with accepted principles of molecular biology. The proposed mechanism of derepression-induced hypermutation provides the critical link between mutations and the metabolic activities evoked by specific conditions of environmental stress, increasing the availability of variants most likely to evolve in that environment.

Percy writes:


Back to the topic. This thread is about the Wright paper's demonstration that environmental factors do not direct evolution in specific directions.

I cannot agree that Wright's paper demonstrates that enviormental facors do not direct evolution in specific directions.
If you read the Wright quote above she seems to be saying that in fact the enviomental factors are directing evolution in specific directions.

I emphasize the later part of her quote:

Wright writes:

However, prolonged nutritional stress results in a general increase in mutation rates; the introduction of environmental effects on specific mutation rates is a reasonable extension of what is known, especially because mechanisms by which starvation can immediately and specifically affect rates of transcription and mutation are consistent with accepted principles of molecular biology. The proposed mechanism of derepression-induced hypermutation provides the critical link between mutations and the metabolic activities evoked by specific conditions of environmental stress, increasing the availability of variants most likely to evolve in that environment.

Am I interpreting this incorrectly?


This message is a reply to:
 Message 105 by Percy, posted 09-24-2011 8:43 PM Percy has responded

Replies to this message:
 Message 107 by Percy, posted 09-25-2011 7:59 PM shadow71 has not yet responded
 Message 109 by Taq, posted 09-26-2011 12:03 PM shadow71 has responded

  
Percy
Member
Posts: 20117
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.4


Message 107 of 296 (635022)
09-25-2011 7:59 PM
Reply to: Message 106 by shadow71
09-25-2011 3:04 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
shadow71 writes:

If you read the Wright quote above she seems to be saying that in fact the enviomental factors are directing evolution in specific directions.

I emphasize the later part of her quote:

Wright writes:

However, prolonged nutritional stress results in a general increase in mutation rates; the introduction of environmental effects on specific mutation rates is a reasonable extension of what is known, especially because mechanisms by which starvation can immediately and specifically affect rates of transcription and mutation are consistent with accepted principles of molecular biology. The proposed mechanism of derepression-induced hypermutation provides the critical link between mutations and the metabolic activities evoked by specific conditions of environmental stress, increasing the availability of variants most likely to evolve in that environment.

Am I interpreting this incorrectly?

Yes, of course you're interpreting this incorrectly. The last sentence, which is what I think you're focusing on, is talking about variants produced by increasing the random mutation rate in a specific region of DNA. The mutations are random with respect to adaptation, but they're occurring in a region with a greater likelihood of having an impact on adaptation in that environment. It represents an improvement over increasing the mutation rate generally throughout the DNA.

--Percy


This message is a reply to:
 Message 106 by shadow71, posted 09-25-2011 3:04 PM shadow71 has not yet responded

  
Taq
Member
Posts: 8482
Joined: 03-06-2009


(2)
Message 108 of 296 (635082)
09-26-2011 11:50 AM
Reply to: Message 104 by shadow71
09-24-2011 8:34 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
If you don't see a reason to inquire as to whether "random mutations and natural selection" is questionalble, then live in your safe little world.

The problem seems to be that you ignore the answers to these questions. I even chose a primary research paper for discussion written by someone that you claim supports your views.

I have met people like yourself before. You are married to a conclusion, the data be damned. I have been very upfront about what random mutations are, how they are tested, and potential falsifications. You, on the otherhand, have not. In your eyes, it doesn't seem to matter what the results of experiments are.

If I am wrong then please show that I am wrong. Please explain how specificity to ssDNA is non-random with respect to fitness. Please explain how the bacteria prevent deleterious and neutral mutations through this mechanism. Also, please explain why the leuB- reversion rate is only 1 in every 500 million divisions.

Edited by Taq, : No reason given.


This message is a reply to:
 Message 104 by shadow71, posted 09-24-2011 8:34 PM shadow71 has not yet responded

Replies to this message:
 Message 119 by zi ko, posted 09-27-2011 5:20 AM Taq has not yet responded

  
Taq
Member
Posts: 8482
Joined: 03-06-2009


(1)
Message 109 of 296 (635083)
09-26-2011 12:03 PM
Reply to: Message 106 by shadow71
09-25-2011 3:04 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
The current paradigm of neo-Darwinism as formulated by Weisman (59) rejects any influence of the environment on the direction of variation.

That is false. Neo-Darwinism did not exist in 1893. It didn't come to fruition until the 1940's, and it has matured since then. Environmental influences on the random mutation rate is a part of the Modern Synthesis (aka neo-Darwinism).

I cannot agree that Wright's paper demonstrates that enviormental facors do not direct evolution in specific directions.
If you read the Wright quote above she seems to be saying that in fact the enviomental factors are directing evolution in specific directions.

The data shows that the environment changes the random mutation rate in genes based on gene upregulation. It is the ssDNA state of the gene which increases the mutation rate, not the need for a specific mutation in that gene. All genes that are actively transcribed, including vital housekeeping genes like gyrase, will see an increase in beneficial, deleterious, and neutral mutations. The processes which produce these mutations are blind to the effects of these mutations on the fitness of the organism.

In fact, we can draw pertinent information from the Lederberg plate replica paper. The Lederbergs' observed that antibiotic resistant mutants arose in the absence of antibiotic. One of those antibiotics binds to the DNA gyrase protein. Mutations in that gene can prevent binding of the antibiotic while preserving gyrase activity. The rate at which these mutants arose is comparable to the leuB- reversion rate as it should be given the fact that gyrase is upregulated at all times.

Am I interpreting this incorrectly?

This is equivalent to people in debt buying more lottery tickets. This increases their chances of getting out of debt, but the lottery is still random. Not only that, but the 1 in 200 million odds of winning the lottery make it a desperate stab at survival, not a proven mechanism for specifically curing someone's debt woes.

If poor people buy more lottery tickets than rich people causing the lottery to be won more often by poor people than rich people does this mean that the lottery is not random but is instead specific for poor people? Does this negate the random nature of the lottery?


This message is a reply to:
 Message 106 by shadow71, posted 09-25-2011 3:04 PM shadow71 has responded

Replies to this message:
 Message 110 by shadow71, posted 09-26-2011 5:03 PM Taq has responded
 Message 113 by Wounded King, posted 09-26-2011 6:53 PM Taq has responded

  
shadow71
Member (Idle past 1870 days)
Posts: 706
From: Joliet, il, USA
Joined: 08-31-2010


Message 110 of 296 (635101)
09-26-2011 5:03 PM
Reply to: Message 109 by Taq
09-26-2011 12:03 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
Wright writes:

The proposed mechanism of derepression-induced hypermutation provides the critical link between mutations and the metabolic activities evoked by specific conditions of environmental stress, increasing the availability of variants most likely to evolve in that environment.

Taq, my question is do you believe Wright is opining by this sentence that these are non-random mutations that are most likely to be beneficial?


This message is a reply to:
 Message 109 by Taq, posted 09-26-2011 12:03 PM Taq has responded

Replies to this message:
 Message 111 by Percy, posted 09-26-2011 5:16 PM shadow71 has not yet responded
 Message 112 by Taq, posted 09-26-2011 6:46 PM shadow71 has responded

  
Percy
Member
Posts: 20117
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.4


Message 111 of 296 (635102)
09-26-2011 5:16 PM
Reply to: Message 110 by shadow71
09-26-2011 5:03 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
Hi Shadow,

You're again asking the same question repeatedly. Let me ask you a question. What do you think Taq was getting at when he asked this of you:

Taz writes:

Also, please explain why the leuB- reversion rate is only 1 in every 500 million divisions.

Hint: It bears directly on the passage from Wright you just quoted.

It is rare in a technical paper for a single sentence to contain all the qualifications and constraints described and explained throughout the paper. There are always going to be sentences in any paper that seem to provide enough wiggle room for you to keep alive the hope that the paper is saying what you wish in your heart it was saying. Cherry picking these sentences isn't going to get you anywhere with people who have read and understood the entire paper. Or as someone says in their signature, we could agree with you, but then we'd all be wrong.

--Percy


This message is a reply to:
 Message 110 by shadow71, posted 09-26-2011 5:03 PM shadow71 has not yet responded

  
Taq
Member
Posts: 8482
Joined: 03-06-2009


Message 112 of 296 (635103)
09-26-2011 6:46 PM
Reply to: Message 110 by shadow71
09-26-2011 5:03 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
Taq, my question is do you believe Wright is opining by this sentence that these are non-random mutations that are most likely to be beneficial?

No, I do not. Wright is stating that hypermutation is an increase in the random mutation rate in genes that are upregulated, exactly what I have been saying all along. This is consistent with the Modern Synthesis, but perhaps not consistent with Weissman's definition of the Modern Synthesis before there was a Modern Synthesis.

Also, Wright states that this hypermutation increase "the availability of variants most likely to evolve in that environment". Wright et al. are hedging their bets against mutations that would be beneficial in genes that are downregulated. This is certainly a possible outcome. Therefore, this mechanism could also lower the probability of specific beneficial mutations occuring in a given environment. There is absolutely no guarantee that every potential beneficial mutation in a given environment will be found in an upregulated gene. I fully believe that Wright et al. would agree with this as well.

If you want to go further down the rabbit hole, you also can not forget that the promoter region of the leuB gene had evolved as a part of a functional leuB gene. If not for the selection of the functional leuB gene and its promoter prior to the experiment there would be no reason for the leuB- gene to be upregulated in the absence of leucine in the first place. If this gene were a sequence that had never been selected for based on past leuB activity then it may have very well been downregulated in an environment lacking leucine.


This message is a reply to:
 Message 110 by shadow71, posted 09-26-2011 5:03 PM shadow71 has responded

Replies to this message:
 Message 115 by shadow71, posted 09-26-2011 7:50 PM Taq has responded

  
Wounded King
Member (Idle past 3030 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 113 of 296 (635104)
09-26-2011 6:53 PM
Reply to: Message 109 by Taq
09-26-2011 12:03 PM


Nitpicks and an interesting reference
Taq writes:

That is false. Neo-Darwinism did not exist in 1893. It didn't come to fruition until the 1940's, and it has matured since then. Environmental influences on the random mutation rate is a part of the Modern Synthesis (aka neo-Darwinism).

This isn't actually correct Taq.

The problem is that terms describing various developments in evolutionary theory over the years have become conflated together, specifically 'Neo-Darwinism' and 'The Modern Synthesis'.

The term neo-darwinism is from a description of Weismann's work by George Romanes another biologist contemporary to Darwin and Weismann. It is a distinction based on the discrete germ line inheritance model of Weismann compared to Darwin's blending inheritance model.

While I'm in my nit-picking mode I'd also direct some at Percy who substantially misrepresented Weismann's position which was principally concerned with the genetic separation between the somatic and germ line cells in metazoa.

Rather than the vague term 'environment' what Weismann studied was whether use and disuse, of specific traits, or physical changes affected inheritance. The sort of Lamarckism Percy seems to be describing in terms of environmental influence is a much more modern conception. Specifically Weismann used mice to study whether docking tails over successive generations would give rise to tailless offspring.

So that is the original concept of Neo-Darwinism and it is distinct form the population genetics based Modern Synthesis of the 30s and 40s.

Just one more thing, not strictly related, while I was searching around for a while ago looking at stuff on different definitions of 'random mutation' I found an article that seems quite pertinent.

Rather unusually for me it isn't from the scientific literature but instead from 'Philosophy and Theory in Biology', an online open-access philosophy journal. The paper is Evolutionary Chance Mutation: A Defense Of the Modern Synthesis’ Consensus View (Merlin, 2010), the abstract reads ...

Merlin writes:

One central tenet of the Modern Evolutionary Synthesis (1930s-1950s), and the consensus view among biologists until now, is that all genetic mutations occur by “chance” or at “random” with respect to adaptation. However, the discovery of some molecular mechanisms enhancing mutation rate in response to environmental conditions has given rise to discussions among biologists, historians and philosophers of biology about the “chance” vs “directed” character of mutations (1980s-2000s). In fact, some argue that mutations due to a particular kind of mutator mechanisms challenge the Modern Synthesis because they are produced when and where needed by the organisms concerned. This paper provides a defense of the Modern Synthesis’ consensus view about the chance nature of all genetic mutations by reacting to Jablonka and Lamb’s analysis of genetic mutations (2005) and the explicit Lamarckian flavor of their arguments. I argue that biologists can continue to talk about chance mutations according to what I call and define as the notion of “evolutionary chance,” which I claim is the Modern Synthesis’ consensus view and a reformulation of Darwin’s most influential idea of “chance” variation. Advances in molecular genetics are therefore significant but not revolutionary with respect to the Modern Synthesis’ paradigm.

Definitely worth a look.

More specifically relevant to this topic is Merlin's critique of the 'directed' interpretation of Wrights work which strongly echoes what Taq has been saying throughout this thread ...

Merlin (2010) writes:

The beneficial mutation at the level of the leuB gene fulfills the first but not the second condition to be a “directed” mutation and is therefore an “evolutionary chance” mutation according to the Modern Synthesis’ consensus view (see above, Section 5). The mutation from LeuB- to LeuB+ is more probable in an environment where bacteria are in leucine starvation than in an environment where the mutation is neutral or deleterious (e.g., in a milieu rich in leucine). This is due to the increase of the mutation rate targeted at the leu operon in response to leucine deprivation. However, the probability of this beneficial reverse mutation occurring is not higher than for other neutral or deleterious mutations in the same leucine deprived environment. In fact, Wright and her colleagues observed that this increased mutation rate is not only targeted at the leuB gene, where a mutation could allow bacteria to survive and reproduce, but at all the genes of the leu operon as well. Therefore, the reverse beneficial mutations at the level of the leuB gene may seem to be “directed” simply because it is easier to detect than mutations occurring in these other genes, which may either grow slower or be negatively selected. Thus, since bacteria carrying the reverse beneficial mutation from LeuB- to LeuB+ are positively selected and contribute to the next generation, they can be easier to detect and quantify than bacteria with other mutations.

TTFN,

WK

Edited by Wounded King, : No reason given.

Edited by Wounded King, : No reason given.


This message is a reply to:
 Message 109 by Taq, posted 09-26-2011 12:03 PM Taq has responded

Replies to this message:
 Message 114 by Taq, posted 09-26-2011 7:38 PM Wounded King has not yet responded
 Message 117 by Percy, posted 09-26-2011 8:25 PM Wounded King has responded

  
Taq
Member
Posts: 8482
Joined: 03-06-2009


Message 114 of 296 (635106)
09-26-2011 7:38 PM
Reply to: Message 113 by Wounded King
09-26-2011 6:53 PM


Re: Nitpicks and an interesting reference
The problem is that terms describing various developments in evolutionary theory over the years have become conflated together, specifically 'Neo-Darwinism' and 'The Modern Synthesis'.

The term neo-darwinism is from a description of Weismann's work by George Romanes another biologist contemporary to Darwin and Weismann. It is a distinction based on the discrete germ line inheritance model of Weismann compared to Darwin's blending inheritance model.

While I'm in my nit-picking mode I'd also direct some at Percy who substantially misrepresented Weismann's position which was principally concerned with the genetic separation between the somatic and germ line cells in metazoa.

Rather than the vague term 'environment' what Weismann studied was whether use and disuse, of specific traits, or physical changes affected inheritance. The sort of Lamarckism Percy seems to be describing in terms of environmental influence is a much more modern conception. Specifically Weismann used mice to study whether docking tails over successive generations would give rise to tailless offspring.

So that is the original concept of Neo-Darwinism and it is distinct form the population genetics based Modern Synthesis of the 30s and 40s.

Fair enough. Nonetheless, I am arguing from the position that mutations are random with respect to fitness, or adaptation as described by Merlin. This seems to conflict with shadow's view of how biology works. A rose by any other name . . .

Merlin (2010) writes:
The beneficial mutation at the level of the leuB gene fulfills the first but not the second condition to be a “directed” mutation and is therefore an “evolutionary chance” mutation according to the Modern Synthesis’ consensus view (see above, Section 5). The mutation from LeuB- to LeuB+ is more probable in an environment where bacteria are in leucine starvation than in an environment where the mutation is neutral or deleterious (e.g., in a milieu rich in leucine). This is due to the increase of the mutation rate targeted at the leu operon in response to leucine deprivation. However, the probability of this beneficial reverse mutation occurring is not higher than for other neutral or deleterious mutations in the same leucine deprived environment. In fact, Wright and her colleagues observed that this increased mutation rate is not only targeted at the leuB gene, where a mutation could allow bacteria to survive and reproduce, but at all the genes of the leu operon as well. Therefore, the reverse beneficial mutations at the level of the leuB gene may seem to be “directed” simply because it is easier to detect than mutations occurring in these other genes, which may either grow slower or be negatively selected. Thus, since bacteria carrying the reverse beneficial mutation from LeuB- to LeuB+ are positively selected and contribute to the next generation, they can be easier to detect and quantify than bacteria with other mutations.

The original Luria-Delbruck paper may actually give us some insight into this. They didn't know it at the time, but the mutations that confer resistance to T1 phage occur in the tonB gene in E. coli. This is a protein that has high turnover and is consitutuitively expressed (i.e. always upregulated). In addition to serving as a binding site for T1 phage it is also a part of the vitamin B12 transport system that moves the vitamin from the environment into the cell (here is a good paper on tonB function). A bacterium without this function will be less adapted than one with this function. At the same time, a dysfunctional tonB gene will allow the bacterium to survive in the presence of T1 phage. Therefore, the selection methods used by Luria and Delbruck actually selected for a deleterious mutation in the environment in which the mutation occurred. This deleterious mutation is produced by the same mechanism as the leuB- reversions, and at a comparable rate.

Edited by Taq, : No reason given.


This message is a reply to:
 Message 113 by Wounded King, posted 09-26-2011 6:53 PM Wounded King has not yet responded

  
shadow71
Member (Idle past 1870 days)
Posts: 706
From: Joliet, il, USA
Joined: 08-31-2010


Message 115 of 296 (635108)
09-26-2011 7:50 PM
Reply to: Message 112 by Taq
09-26-2011 6:46 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
Merlin in the paper cited by Wounded King writes:

The main purpose of this paper is to defend the “chance” character of genetic mutations, which I claim is a Darwinian tenet and part of the Modern Synthesis’ consensus view, against recent challenges, especially those advanced by Jablonka and Lamb (1995, 2005). During the last thirty years, experimental research in molecular genetics, in particular on microorganisms, has shown that certain molecular mechanisms – the so-called “mutator mechanisms” – can regulate mutation rates (increasing or decreasing them) in response to certain selective forces. Because of this causal connection between mutation rates and selective substrates, Jablonka and Lamb, along with other biologists, historians and philosophers of biology (Shapiro 1999, 2005;

Wright et al. 1999, 2000; Sternberg 2002; Keller 2000), have questioned the Modern Synthesis’ claim that all genetic mutations occur by “chance” or at “random.”

From Message 112 by Taq:

Shadow 71 asks;

Taq, my question is do you believe Wright is opining by this sentence that these are non-random mutations that are most likely to be beneficial?

taq writes:


No, I do not. Wright is stating that hypermutation is an increase in the random mutation rate in genes that are upregulated, exactly what I have been saying all along. This is consistent with the Modern Synthesis, but perhaps not consistent with Weissman's definition of the Modern Synthesis before there was a Modern Synthesis.

The paper cited by Wounded King clearly states that Wright et. al. including Shaprio challenge the Modern Synthesis claim that all genetic mutation occur by chance or at random.

So your interpretation of Wright's opinion is challenged by Merlin. You may or may not be correct about mutations being random, but my reading of Wright is correct. She is in fact challenging whether all mutations are random in the paper you cited. So both you and Percy should read my messages more carefully, and not jump to conclusions, such as Percy's, that I am "daft".
If you read Wright's paper carefully it is clear she is challenging this Modern Synthesis point.


This message is a reply to:
 Message 112 by Taq, posted 09-26-2011 6:46 PM Taq has responded

Replies to this message:
 Message 116 by Taq, posted 09-26-2011 7:53 PM shadow71 has responded
 Message 118 by Percy, posted 09-26-2011 9:09 PM shadow71 has responded

  
Taq
Member
Posts: 8482
Joined: 03-06-2009


Message 116 of 296 (635109)
09-26-2011 7:53 PM
Reply to: Message 115 by shadow71
09-26-2011 7:50 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
The paper cited by Wounded King clearly states that Wright et. al. including Shaprio challenge the Modern Synthesis claim that all genetic mutation occur by chance or at random.

Wright didn't show that in this paper, and it was never stated outright in the section you quoted.

Even more importantly, the data does not support non-random mutations. Wright's opinion does not trump the data.


This message is a reply to:
 Message 115 by shadow71, posted 09-26-2011 7:50 PM shadow71 has responded

Replies to this message:
 Message 125 by shadow71, posted 09-27-2011 12:47 PM Taq has responded

  
Percy
Member
Posts: 20117
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.4


Message 117 of 296 (635112)
09-26-2011 8:25 PM
Reply to: Message 113 by Wounded King
09-26-2011 6:53 PM


Re: Nitpicks and an interesting reference
Even after reading your excerpts from 'Philosophy and Theory in Biology', an online open-access philosophy journal, and after rereading key portions of the Wright paper, I couldn't see how this philosophy/biology paper arrives at the conclusion that Wright is endorsing directed evolution. Do you agree with this paper's interpretation? If so, can you help us out here?

--Percy


This message is a reply to:
 Message 113 by Wounded King, posted 09-26-2011 6:53 PM Wounded King has responded

Replies to this message:
 Message 120 by Wounded King, posted 09-27-2011 5:42 AM Percy has responded

  
Percy
Member
Posts: 20117
From: New Hampshire
Joined: 12-23-2000
Member Rating: 3.4


Message 118 of 296 (635116)
09-26-2011 9:09 PM
Reply to: Message 115 by shadow71
09-26-2011 7:50 PM


Re: Do you agree that this specificity is not compatable with NeoRe: beneficial mutations
shadow71 writes:

So both you and Percy should read my messages more carefully, and not jump to conclusions, such as Percy's, that I am "daft".

You were called daft because you were parroting the exact same question in the face of repeated answers as if it were some kind of profound search for knowledge deserving of respect. It had nothing to do with your interpretation of the Wright paper, but you then continued your daft behavior by repeatedly quoting the same Wright passage and asking the same question.

Merlin's interpretation of the Wright paper is as wrongheaded as your own. Wright never claims directed mutations, and that's a good thing, because her data doesn't support directed mutations.

Maybe WK will make the case for how the Wright paper endorses directed mutations.

--Percy


This message is a reply to:
 Message 115 by shadow71, posted 09-26-2011 7:50 PM shadow71 has responded

Replies to this message:
 Message 126 by shadow71, posted 09-27-2011 1:32 PM Percy has responded

  
zi ko
Member (Idle past 2555 days)
Posts: 578
Joined: 01-18-2011


Message 119 of 296 (635134)
09-27-2011 5:20 AM
Reply to: Message 108 by Taq
09-26-2011 11:50 AM



If I am wrong then please show that I am wrong. Please explain how specificity to ssDNA is non-random with respect to fitness. Please explain how the bacteria prevent deleterious and neutral mutations through this mechanism. Also, please explain why the leuB- reversion rate is only 1 in every 500 million divisions.

I suppose mutations inlelation to fitness are random, but are they random in relation to life perservance? This i think is the crucial question. Randomness in relation to fintness could mean nothing,if it is not random in relation to life percervance, which actually shows the "Designer", or the "thinking" Nature, according to my information hypothesis.

Edited by zi ko, : No reason given.


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 Message 108 by Taq, posted 09-26-2011 11:50 AM Taq has not yet responded

Replies to this message:
 Message 124 by Percy, posted 09-27-2011 7:15 AM zi ko has responded

  
Wounded King
Member (Idle past 3030 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 120 of 296 (635137)
09-27-2011 5:42 AM
Reply to: Message 117 by Percy
09-26-2011 8:25 PM


Re: Nitpicks and an interesting reference
Well to some extent you have to look outside of this specific paper by Wright, the other Wright paper Merlin cites is entitled "A Biochemical Mechanism for Nonrandom Mutations and Evolution". It is also worth bearing in mind that it is Wright who claims that her research is overturning 'current neo-Darwinian dogma'.

If one should equate non-random with directed is another question and one that the Merlin paper deals with at length. If you feel that Wright's 'non-random' mutational claims are distinct from claims of 'directed' mutation then fair enough. Merlin is more focused on the way the work has been presented by Jablonka and Lamb in their book "Evolution in 4 dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life."

Fro the most part Merlin merely describes the actual specifics of Wright's work on the LeuB- strain. The only specific claim of Wright's that Merlin discusses in the paper is that ...

On the basis of these results, Wright and her colleagues suggested that the induced and local hypermutability was an adaptive result of evolution by natural selection, that is, an adaptive response to adverse environmental conditions or, to be more precise, to amino acid starvation.

Merlin contends that this is not in fact an adaptive response even though it was a response that did have the effect of giving rise to an adaptation. Rather the adaptive mutation is simply a by product, due to the increased susceptibility of single stranded DNA, of the metabolic response to Leucine starvation, which is the upregulation of the Leu operon.

It would be interesting to see whether there was a specific increase in beneficial mutations of the Leu operon in a normal LeuB+ strain under starvation. The artificiality of the LeuB- experimental setup produces a possible mutation with such an overbearing selective advantage that one wonders what a more finely detailed approach might throw up. Sadly such experiments are considerably more challenging as with Lenski's long term evolutionary study.

TTFN,

WK


This message is a reply to:
 Message 117 by Percy, posted 09-26-2011 8:25 PM Percy has responded

Replies to this message:
 Message 123 by Percy, posted 09-27-2011 7:13 AM Wounded King has responded

  
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