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 The Great Unknown: Risk-Taking Behavior in Adolescents
19.01.2017 | Max-Planck-Institut für Bildungsforschung

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

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: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>