Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

University of Chicago study overturns conventional theory in evolution

07.06.2005


New data suggest that the accumulation of genetic changes is not solely determined by natural selection. A study by University of Chicago researchers contradicts conventional theory by showing that the percentage of mutations accepted in evolution is also strongly swayed by the speed at which new mutations arrive at a gene: the faster the speed of new mutations, the greater the percentage of those mutations accepted.

"We’ve discovered a striking phenomenon that challenges a paradigm of molecular evolution that has been around for several decades," said lead author Bruce Lahn, Ph.D., assistant professor of genetics at the University of Chicago and Howard Hughes Medical Institute investigator. "As such, it may cause a significant shift in the field."

The researchers report their findings in the July 2005, issue of the journal Trends in Genetics, available early online June 7. Other authors are Gerald Wyckoff, Ph.D., previously a postdoctoral fellow in Lahn’s lab and now an assistant professor at the University of Missouri-Kansas City, and Christine Malcom and Eric Vallender, both graduate students in Lahn’s lab.



For more than three decades, molecular evolutionists have thought that no matter how many genetic mutations show up on a specific gene, whether or not those mutations become fixed in the species is determined primarily by natural selection. The new study shows that the speed at which these new mutations arrive also affects whether the mutations become fixed.

Lahn’s team looked at nearly 6,000 genes in their study. For each gene, they compared sequences between two mammalian species. This enabled them to measure the mutation rate of the gene – specifically, the rate of those mutations that do not affect the protein’s structure, called synonymous mutation (Ks). These mutations are functionally neutral, which means natural selection is not a factor in whether they are accepted during evolution.

Lahn’s team also looked at the mutation rate of nonsynonymous changes (Ka) – the rate of those mutations that do affect protein structure. These mutations are typically subject to natural selection. A nonsynonymous mutation will get accepted into or bounced out of the population based upon how the change alters protein function.

The researchers then studied the Ka/Ks ratio. A low Ka/Ks ratio indicates strong selection; conversely, a high ratio, weak selection. Some genes have a ratio of 0, which means protein changes are not accepted. It is, in a sense, "perfect."

For a pseudogene – a stretch of DNA sequence that resembles a gene but has no function – its Ka/Ks ratio is approximately 1.0, which means that synonymous and nonsynonymous mutations are accepted at the same rate since the gene is functionally irrelevant.

For a gene that is highly functional and important for the organism, its Ka/Ks ratio is typically low. For example, if a gene has a Ka/Ks ratio of 0.1, it means that it’s highly selective and is only accepting 10 percent of the nonsynonymous mutations.

Regardless of the rate of new mutations at a particular gene, scientists have always presumed the percentage of nonsynonymous mutations accepted during evolution remains constant.

"This theory has been the workhorse of molecular evolution," Lahn said. "Thousands of scientific papers have been published based directly or indirectly on this notion."

The new data show that if more mutations show up at a gene, that gene tends to accept a higher percentage of those mutations.

"A gene under strong mutational pressure succumbs to that pressure," Lahn said. "For genes that have a high mutation rate, somehow selection appears to become less stringent."

Lahn cannot explain the mechanism of his findings and expects many will question this novel finding. "It’s too radical," he said. "People just don’t want to believe it, but the data are there."

"Lahn and his associates have found a most striking result, one that is totally unexpected," said geneticist James Crow, professor emeritus of genetics and zoology at the University of Wisconsin-Madison. "If this result is indeed confirmed it would cast doubt on use of this ratio [Ka/Ks] as an indicator of selection."

Sudhir Kumar, an associate professor of molecular evolution at Arizona State University, agreed. "It goes against strict theory, but evolutionary biologists know that nothing’s clean cut. There’s always distortion because we’re looking at longtime history.

"The novelty of this work is that he [Lahn] used a large amount of data," Kumar said. "It’s a perfect example of the power of the genome project."

"I hope that further work will provide an explanation of what now is a major puzzle," Crow added.

Catherine Gianaro | EurekAlert!
Further information:
http://www.uchospitals.edu

More articles from Studies and Analyses:

nachricht New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

nachricht Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>