Freethought & Rationalism Archive

Elijah · 07-08-2007, 10:00 AM

Quote:

Originally Posted by The Evil One

Um "mutagenesis"? As in mutations to the genes? As in, the mechanism of change in neo-Darwinism, not Lamarckism?

Just read up on it.

someotherguy · 07-08-2007, 10:26 AM

Quote:

Originally Posted by Elijah

Quote:

Originally Posted by The Evil One

Um "mutagenesis"? As in mutations to the genes? As in, the mechanism of change in neo-Darwinism, not Lamarckism?

Just read up on it.

Okay. From Wikipedia:

Quote:

Directed mutagenesis, also known as directed mutation, is a largely discredited hypothesis proposing that organisms can respond to environmental stresses through directing mutations to certain genes or areas of the genome.

The hypothesis was first proposed in 1988 by John Cairns, of Harvard University,[citation needed] who was studying Escherichia coli that lacked the ability to metabolize lactose. He grew these bacteria in media in which lactose was the only source of energy. In doing so, he found that the rate at which the bacteria evolved the ability to metabolize lactose was many orders of magnitude higher than would be expected if the mutations were truly random. This inspired him to propose that the mutations that had occurred had been directed at those genes involved in lactose utilization.

Later support for this hypothesis came from Susan Rosenberg, then at the University of Alberta, who found that an enzyme involved in DNA recombinational repair, recBCD, was necessary for the directed mutagenesis observed by Cairns and colleagues in 1989.

However, the directed mutagenesis hypothesis was essentially disproved in 2002, when John Roth and colleagues showed that the phenomenon was due to general hypermutability due to selected gene amplification, and was thus a "standard Darwinian process."

Emphasis added.

Elijah · 07-08-2007, 10:30 AM

Quote:

Originally Posted by someotherguy

However, the directed mutagenesis hypothesis was essentially disproved in 2002, when John Roth and colleagues showed that the phenomenon was due to general hypermutability due to selected gene amplification, and was thus a "standard Darwinian process."

Emphasis added.

Another test will say something else later, I'm sure.

Edit add link... fix box

https://notes.utk.edu/bio/greenberg....5?OpenDocument

ck1 · 07-08-2007, 10:59 AM

Quote:

Originally Posted by Elijah

From wiki on lamarckism.

"In 1988, John Cairns at the Radcliffe Infirmary in Oxford, England, and a group of other scientists renewed the Lamarckian controversy (which by then had been a dead debate for many years).[4] The group took a mutated strain of E. coli that was unable to consume the sugar lactose and placed it in an environment where lactose was the only food source. They observed over time that mutations occurred within the colony at a rate that suggested the bacteria were overcoming their handicap by altering their own genes. Cairns, among others, dubbed the process adaptive mutagenesis."

http://www.springerlink.com/content/vwr160460x397667/

Your comment brings to mind SOS polymerases, and from the link above, this may explain this phenomenon at least in part.

(I am under a time constraint and the following is from memory, and may need some editing.) E. coli have 5 DNA polymerases used in replication. Several of these are not normally expressed but are induced during times of stress, particularly when the cells are exposed to radiation or DNA-damaging chemicals. These polymerases are able to replicate DNA even when it is broken, but they have a much higher error rate in replicating non-damaged DNA. So when bacteria are stressed, these polymerases become active and generate a higher than normal mutation rate. So more of the bacteria die, but the higher mutation rate is also more likely to generate mutations that has survival benefits. This can explain the results you cited above. This provides a perfectly natural explanation for the observed phenomenon and it is not Lamarckianism.

Added note - There is at least one study showing that deletion of the SOS polymerase genes severely impairs the ability of bacteria to produce drug-resistance mutants.

Elijah · 07-08-2007, 11:15 AM

Quote:

Originally Posted by ck1

(I am under a time constraint and the following is from memory, and may need some editing.) E. coli have 5 DNA polymerases used in replication. Several of these are not normally expressed but are induced during times of stress, particularly when the cells are exposed to radiation or DNA-damaging chemicals. These polymerases are able to replicate DNA even when it is broken, but they have a much higher error rate in replicating non-damaged DNA. So when bacteria are stressed, these polymerases become active and generate a higher than normal mutation rate. So more of the bacteria die, but the higher mutation rate is also more likely to generate mutations that has survival benefits. This can explain the results you cited above. This provides a perfectly natural explanation for the observed phenomenon and it is not Lamarckianism.

Added note - There is at least one study showing that deletion of the SOS polymerase genes severely impairs the ability of bacteria to produce drug-resistance mutants.

My feeling is that the stimuli on an organism creates predictable changes. Even radiation on the cells, if we could understand fully all the factors going into it. I'm not much for the accelerating the rate of genetic mistakes idea. I'm for actual physical stimuli creating corresponding affects on the organism that could be passed on.

TomboyMom · 07-08-2007, 11:27 AM

Why would we be interested in your feelings or beliefs? Do you have er, evidence? That would impress us much more.

Elijah · 07-08-2007, 11:34 AM

Quote:

Originally Posted by TomboyMom

Why would we be interested in your feelings or beliefs? Do you have er, evidence? That would impress us much more.

Did you look at the link I posted?

ck1 · 07-08-2007, 12:41 PM

Quote:

Originally Posted by Elijah

My feeling is that the stimuli on an organism creates predictable changes. Even radiation on the cells, if we could understand fully all the factors going into it. I'm not much for the accelerating the rate of genetic mistakes idea. I'm for actual physical stimuli creating corresponding affects on the organism that could be passed on.

Interesting link on epigenetics, thanks.

There are multiple factors that alter gene expression - methylation being one of them. This phenomenon has been under investigation for a long time and its role, for example, in imprinting, is well documented. It also seems to me that this is a sophisticated way for organisms to respond to temporary fluctuations in their environments. But it does not result in a permanent change in the lineage which is what evolution is all about.

You seem to be suggesting that this type of phenomenon has a greater role than DNA level mutational changes in terms of the evolutionary adaptations we see. If that is what you are saying, you need to provide more support, because I sure don't see that in the scientific literature.

And accelerating genetic mistakes through the SOS system is supported by experimental data.

Elijah · 07-08-2007, 12:53 PM

Quote:

Originally Posted by ck1

Interesting link on epigenetics, thanks.

There are multiple factors that alter gene expression - methylation being one of them. This phenomenon has been under investigation for a long time and its role, for example, in imprinting, is well documented. It also seems to me that this is a sophisticated way for organisms to respond to temporary fluctuations in their environments. But it does not result in a permanent change in the lineage which is what evolution is all about.

You seem to be suggesting that this type of phenomenon has a greater role than DNA level mutational changes in terms of the evolutionary adaptations we see. If that is what you are saying, you need to provide more support, because I sure don't see that in the scientific literature.

And accelerating genetic mistakes through the SOS system is supported by experimental data.

I just don't see the genetic changes as mistakes. Not sure what phenomenon you are talking about.

SpaghettiSawUs · 07-08-2007, 01:51 PM

Quote:

Originally Posted by Elijah

I just don't see the genetic changes as mistakes. Not sure what phenomenon you are talking about.

You seem to be having difficulty with the term "mistake". In this context it is merely a copying error, a difference between the source DNA and the resultant DNA. If any of those changes give rise to the synthesis of a new protein - one having beneficial results for the survival fitness of the organism - then you have random change (a "mistake or error" in copying) producing novel function and survival fitness. Most mistakes do not have this result, they are mainly neutral or mal-adaptive, the latter being selected out.

It follows that by increasing the mutation rate, within a large enough population, increases the odds of a beneficial mutation occurring. This seems to be what happened with Escherichia coli, which, coupled with strong selection pressure within the environment, found a way (through genetic mutation) to survive in a hostile environment.

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07-08-2007, 11:27 AM	#16
TomboyMom Contributor Join Date: Jan 2003 Posts: 10,931	Why would we be interested in your feelings or beliefs? Do you have er, evidence? That would impress us much more.

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