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Chapter 17 : How Bacteria Revealed Darwin's Mistake (and Got Me To Read )

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How Bacteria Revealed Darwin's Mistake (and Got Me To Read ), Page 1 of 2

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Abstract:

Charles Darwin really could have used bacteria, organisms for which you can really measure mutation rates. Astronomical populations of bacteria can be grown with and without stress and their mutation types can be characterized. In fact bacteria helped Lederberg, Luria, and Delbrück show that new mutations can form without any required "stress." Mutants arise continuously in perfectly happy bacterial populations. With great excitement Darwin showed the data (obtained using bacteria) suggesting that Lederberg, Luria, and Delbrück had missed something-Darwin might have been closer to the mark than people realized. The key to evaluating Cairns claims lies in the details of his selection conditions. Small-effect mutations are extremely common, and they can contribute serially to very fast strain improvement. It seems that the mechanisms for DNA replication and repair have evolved to be most effective at preventing mutation types with large phenotypic effects. All of laboratory bacterial genetics use the same principle strong selection. The trick is to block all parent cell growth (no new mutations) and prevent growth of those annoying frequent small-effect mutations. Darwin’s idea of stress-induced mutation may be wrong, but natural selection can take on breathtaking power when common small-effect mutations are allowed to contribute. These effects are revealed by bacterial populations. Under selection, the high speed of genetic adaptation is easily mistaken for an increase in mutation rate—maybe even Darwin underestimated the power of selection.

Citation: Roth J. 2012. How Bacteria Revealed Darwin's Mistake (and Got Me To Read ), p 123-131. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch17

Key Concept Ranking

Frameshift Mutation
0.71505374
Point Mutation
0.6877791
Escherichia coli
0.50555557
Natural Selection
0.4969322
0.71505374
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Figures

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Figure 1

Mutation types vary in their formation rate over a millionfold range. In general, the most frequent mutation types are those with the smallest effects on phenotype. This is true for both increases and decreases in gene activity. doi:10.1128/9781555818470.ch17f1

Citation: Roth J. 2012. How Bacteria Revealed Darwin's Mistake (and Got Me To Read ), p 123-131. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch17
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Image of Figure 2
Figure 2

Selection causes an exponential increase in mutant frequency and is most likely to act on the most common mutations, which often have the smallest phenotypic change. Each mutation leads to expansion of a subclone in which subsequent common mutations can further enhance growth ability. doi:10.1128/9781555818470.ch17f2

Citation: Roth J. 2012. How Bacteria Revealed Darwin's Mistake (and Got Me To Read ), p 123-131. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch17
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Image of Figure 3
Figure 3

The Cairns experiment allows slow growth of very common small-effect mutants (with a duplication). These mutants initiate clones that adapt by a multistep pathway during the prolonged (6-day) selection period. Many of these clones succeed in generating full-sized Lac colonies, which first appear at various times over the selection period. doi:10.1128/9781555818470.ch17f3

Citation: Roth J. 2012. How Bacteria Revealed Darwin's Mistake (and Got Me To Read ), p 123-131. In Kolter R, Maloy S (ed), Microbes and Evolution. ASM Press, Washington, DC. doi: 10.1128/9781555818470.ch17
Permissions and Reprints Request Permissions
Download as Powerpoint

References

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