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Topic: Under Pressure, Does Evolution Evolve?
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roxrkool
Member (Idle past 989 days) Posts: 1497 From: Nevada Joined: 03-23-2003
(2)
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Message 1 of 7 (718920)
02-09-2014 4:01 PM
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quote:
Under Pressure, Does Evolution Evolve? In 1996, Susan Rosenberg, then a young professor at the University of Alberta, undertook a risky and laborious experiment. Her team painstakingly screened hundreds of thousands of bacterial colonies grown under different conditions, filling the halls outside her lab with tens of thousands of plates of bacteria. It stank, Rosenberg recalled with a laugh. My colleagues hated me. The biologist, now at Baylor College of Medicine in Houston, hoped to resolve a major debate that had rocked biology in different incarnations for more than 100 years. Were organisms capable of altering themselves to meet the needs of their environment, as Jean Baptiste Lamarck had proposed in the early 1800s? Or did mutations occur randomly, creating a mixture of harmful, harmless or beneficial outcomes, which in turn fueled the trial-and-error process of natural selection, as Charles Darwin proposed in On the Origin of Species? Although Darwin’s ideas have clearly triumphed in modern biology, hints of a more Lamarckian style of inheritance have continued to surface. Rosenberg’s experiments were inspired by a controversial study, published in the late 1980s, that suggested that bacteria could somehow direct their evolution, choosing which mutations will occur, the authors wrote a modern molecular biologist’s version of Lamarckian theory. Rosenberg’s results, published in 1997, disputed those findings, as other’s had before, but with a twist. Rather than targeting specific traits, as Lamarck’s theory would have predicted, the mutations struck random genes, with some good outcomes and some bad. However, the process wasn’t completely random. Rosenberg’s findings suggested that bacteria were capable of increasing their mutation rates, which might in turn produce strains capable of surviving new conditions. Cells are able to adapt to stress not by knowing exactly what they need to do, but by throwing the dice as a population and making random changes to the genome, said James Broach, a biologist at Pennsylvania State University’s College of Medicine in Hershey who studies a similar phenomenon in yeast. That will allow stressed progeny to find an escape route. Rosenberg expected the biology community to be relieved. Darwin, after all, had prevailed. But some scientists questioned the findings. Indeed, the research triggered debates that played out in the pages of scientific journals for several years. Accurately measuring mutation rates can be tricky, and given that most mutations are harmful to the cell, boosting their frequency seemed like a risky evolutionary move. Over the past decade, however, labs around the world have found similar patterns in bacteria, human cancer cells and plants. And Rosenberg and others have pinpointed the molecular mechanisms underlying the stress-induced mutations, which vary from organism to organism.
... the rest of the story
Replies to this message: | | Message 2 by Taq, posted 02-11-2014 1:35 PM | | roxrkool has not replied |
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Taq
Member Posts: 9973 Joined: 03-06-2009 Member Rating: 5.7
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Message 2 of 7 (719110)
02-11-2014 1:35 PM
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Reply to: Message 1 by roxrkool 02-09-2014 4:01 PM
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From the article: "However, the process wasn’t completely random. Rosenberg’s findings suggested that bacteria were capable of increasing their mutation rates, which might in turn produce strains capable of surviving new conditions." Increasing the random mutation rate still produces random mutations. I see this mistake made by the press and scientists alike. The randomness of mutations has to do with their relation to fitness, not time, genomic loci, or rate. As an analogy, you can increase the number of lottery drawings, but the results are still random. Poor people can buy more tickets than rich people, but the results are still random. One area of the country can buy more tickets than other areas, but the results are still random.
This message is a reply to: | | Message 1 by roxrkool, posted 02-09-2014 4:01 PM | | roxrkool has not replied |
Replies to this message: | | Message 3 by RAZD, posted 02-11-2014 2:10 PM | | Taq has replied |
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RAZD
Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: 03-14-2004
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Message 3 of 7 (719114)
02-11-2014 2:10 PM
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Reply to: Message 2 by Taq 02-11-2014 1:35 PM
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Increasing the random mutation rate still produces random mutations. I see this mistake made by the press and scientists alike. The randomness of mutations has to do with their relation to fitness, not time, genomic loci, or rate. Several different mechanism have been found iirc that reduce the error correction\counteraction, allowing more mutations that would otherwise be constricted. Is it possible that some of these mechanisms affect some sections of the DNA more\less than others (are some sections more highly conserved)?
This message is a reply to: | | Message 2 by Taq, posted 02-11-2014 1:35 PM | | Taq has replied |
Replies to this message: | | Message 4 by Taq, posted 02-11-2014 3:16 PM | | RAZD has replied |
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Taq
Member Posts: 9973 Joined: 03-06-2009 Member Rating: 5.7
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Message 4 of 7 (719119)
02-11-2014 3:16 PM
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Reply to: Message 3 by RAZD 02-11-2014 2:10 PM
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Several different mechanism have been found iirc that reduce the error correction\counteraction, allowing more mutations that would otherwise be constricted. Is it possible that some of these mechanisms affect some sections of the DNA more\less than others (are some sections more highly conserved)?
There is no doubt that some areas of a genome will experience higher mutation rates than others. However, whether a mutation occurs or not is not determined by the needs of the organism. The classic example of the SOS mutation response was seen with E. coli and lac+ revertants. In this experiments, starvation caused a higher rate of mutations that resulted in the ability to metabolize lactose when lactose was present. However, it was soon found that these mutations would occur at the same rate whether lactose was present or not. It was the starvation that caused the increased the genome wide mutation rate, not the presence of lactose.
This message is a reply to: | | Message 3 by RAZD, posted 02-11-2014 2:10 PM | | RAZD has replied |
Replies to this message: | | Message 5 by RAZD, posted 02-11-2014 3:37 PM | | Taq has replied |
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RAZD
Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: 03-14-2004
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Message 5 of 7 (719122)
02-11-2014 3:37 PM
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Reply to: Message 4 by Taq 02-11-2014 3:16 PM
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There is no doubt that some areas of a genome will experience higher mutation rates than others. ... Would you say that the areas that are more highly conserved would be ones where mutations are more likely to be lethal?
This message is a reply to: | | Message 4 by Taq, posted 02-11-2014 3:16 PM | | Taq has replied |
Replies to this message: | | Message 6 by Taq, posted 02-11-2014 4:22 PM | | RAZD has replied |
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Taq
Member Posts: 9973 Joined: 03-06-2009 Member Rating: 5.7
(1)
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Message 6 of 7 (719129)
02-11-2014 4:22 PM
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Reply to: Message 5 by RAZD 02-11-2014 3:37 PM
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Would you say that the areas that are more highly conserved would be ones where mutations are more likely to be lethal? On average, yes. This could be confirmed by the ratio of synonymous and non-synonymous mutations. The rate of divergence due to neutral synonymous mutations should give you the rate of mutation. This would allow you to measure selection based on the rate of accumulation of non-synonymous mutations, the famous Ka/Ks ratio.
This message is a reply to: | | Message 5 by RAZD, posted 02-11-2014 3:37 PM | | RAZD has replied |
Replies to this message: | | Message 7 by RAZD, posted 02-11-2014 6:03 PM | | Taq has not replied |
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RAZD
Member (Idle past 1405 days) Posts: 20714 From: the other end of the sidewalk Joined: 03-14-2004
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Message 7 of 7 (719137)
02-11-2014 6:03 PM
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Reply to: Message 6 by Taq 02-11-2014 4:22 PM
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On average, yes. ... So - on average - the increase in mutation rate would be skewed slightly to less lethally deleterious mutations, but the rest is wide open random? On average then, it could be argued that there is slightly increased beneficial\neutral mutations in proportion to total mutations? Not by knowing what would be beneficial\neutral, but by knowing what is lethally deleterious and reducing those? Edited by RAZD, : .
This message is a reply to: | | Message 6 by Taq, posted 02-11-2014 4:22 PM | | Taq has not replied |
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