May 20th, 2006

homuncul

МЕТОДОЛОГИЯ

в PLos Biology не доверяют 'молекулярным часам'


...genetic distances are rather crude indicators of evolutionary history. A small genetic distance between two sequences may suggest a recent common ancestor, but is also consistent with a slower rate of sequence change and a more ancient common ancestor (i.e., genetic distance = evolutionary rate × time). Genetic distances alone are therefore of little use if, for example, we wish to know the age of the common ancestor of mammals, or the rate at which bacterial antibiotic resistance genes evolve. Such questions can be answered only if independent information about rates or divergence times is found. Often paleontology or biogeography can provide a date for one or more points in a phylogeny, which are then used to “calibrate” the timescale for the rest of the phylogeny.


Whatever the source of the independent information, it is usual to calibrate a phylogeny by assuming that all its branches evolve at the same rate—i.e., there is a constant but stochastic “molecular clock” of sequence change. The concept of the molecular clock originated in the early 1960s and has since been used widely, more as a result of its downright usefulness than its biological accuracy, as it is clear that rates of evolution can and do vary considerably among species. Evolutionary rates depend on a combination of factors: generation time, population size, metabolic rate, the efficacy of DNA repair, and the degree to which mutations are beneficial or deleterious, all of which may vary among species. As the geneticist Steve Jones recently remarked, evolutionary biologists seem to use the molecular clock “with our fingers crossed”.


PLoS Biology, May 2006
Model Selection and the Molecular Clock


Похоже, не только в PLos Biol. но также и в
PNAS, May 2006
There is no universal molecular clock for invertebrates, but rate variation does not scale with body size


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К вопросу о последних "неожиданных результатах"...(по мне просто казусах из-за некорректных моделей)
homuncul

ЭВОЛЮЦИЯ

и все-таки они не случайны!..


In this week's Molecular Cell, Rice University biologists describe how they stripped heat-loving bacteria of a key metabolic gene and then forced them to adapt by slowly raising the temperature of their habitat. The identical genetic adaptation won out in repeated experiments, suggesting a repeatable pattern of molecular adaptation.


...Though millions of mutations in the target gene are believed to have occurred, only about 700 of those were capable of creating a new variant of the target gene. In all, the researchers identified 343 unique strains, each of which contained one of just six variants of the critical gene.
...The research included a raft of additional experiments as well. The team characterized each of the mutant proteins to document precisely how it aided in metabolic regulation. The fermentor experiment was repeated and the same mutations - and no others - were observed to develop again.

"One of our most surprising findings is that an estimated 20 million point mutations gave rise to just six populations that were capable of vying for dominance," said lead researcher Yousif Shamoo, associate professor of biochemistry and cell biology. "This suggests that very few molecular pathways are available for a specific molecular response".

Shamoo said the most promising finding is the fact that the follow-up test produced precisely the same mutant genes.



"Ready, set, mutate..." Rice Univercity press release (05/18/2006)
One-Track Evolution

Molecular Cell, Vol 22, 441-449, 19 May 2006
"In Vivo Molecular Evolution Reveals Biophysical Origins of Organismal Fitness", abstract , DOI


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то, о чем так долго говорили большевики....
см. также http://nature-wonder.livejournal.com/40903.html
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