Evolution Caught in the Act: Scientists Measure How Quickly Genomes Change

[steven johnson]

While mutation rates of DNA have been estimated to calibrate a "molecular clock" indicating time since species had a common ancestor. There is a 'circular argument' in this clock's calibration. Until now, there is very little experimental data on the actual rate of of this mutation rate. Here is a study in plants that purports to suggest what the real rate might be.

http://www.detectingdesign.com/dnamutationrates.html

ScienceDaily (Jan. 3, 2010) — Mutations are the raw material of evolution. Charles Darwin already recognized that evolution depends on heritable differences between individuals: those who are better adapted to the environment have better chances to pass on their genes to the next generation. A species can only evolve if the genome changes through new mutations, with the best new variants surviving the sieve of selection...Their findings shed new light on a fundamental evolutionary process. They explain, for example, why resistance to herbicides can appear within just a few years.

The painstakingly detailed comparison of the entire genome (five lines of the mustard relative Arabidopsis thaliana) revealed that in over the course of only a few years some 20 DNA building blocks, so called base pairs, had been mutated in each of the five lines. "The probability that any letter of the genome changes in a single generation is thus about one in 140 million," explains Michael Lynch. To put it differently, each seedling has on average one new mutation in each of the two copies of its genome that it inherits from mum and dad. To find these tiny alterations in the 120 million base pair genome of Arabidopsis was akin to finding the proverbial needle in a haystack, says Weigel: "To ferret out where the genome had changed was only possibly because of new methods that allowed us to screen the entire genome with high precision and in very short time." Still, the effort was daunting: To distinguish true new mutations from detection errors, each letter in each genome had to be checked 30 times.

The number of new mutations in each individual plant might appear very small. But if one starts to consider that they occur in the genomes of every member of a species, it becomes clear how fluid the genome is: In a collection of only 60 million Arabidopsis plants, each letter in the genome is changed, on average, once. For an organism that produces thousands of seeds in each generation, 60 million is not such a big number at all.

urning to the larger picture, Weigel suggests that changes in the human genome are at least as rapid as in Arabidopsis: "If you apply our findings to humans, then each of us will have on the order of 60 new mutations that were not present in our parents." With more than six billion people on our planet, this implies that on average each letter of the human genome is altered in dozens of fellow citizens. "Everything that is genetically possible is being tested in a very short period," adds Lynch, emphasizing a very different view than perhaps the one we are all most familiar with: that evolution reveals itself only after thousands, if not millions of years.

Evolution Caught in the Act: Scientists Measure How Quickly Genomes Change

[Poll_Blind]

1. Very....VERY cool. K&R! n/t

PB

[gristy]

2. It dawned on me today that random changes on the genome is itself a product

of evolution. Imagine a form of life somehow coming into existence whose genome is frozen. It would have no ability to adapt to changing circumstances, competition, climate, etc. It would die out. Only those that can adapt (through random changes in the genome) will evolve to survive such changes.

The finer point here is that the nature of life that requires random changes in the genome may be an evolution-induced trait itself.