Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

DNA analysis for chimpanzees and humans reveals striking differences in genes for smell, metabolism and hearing

19.12.2003


Nearly 99 percent alike in genetic makeup, chimpanzees and humans might be even more similar were it not for what researchers call "lifestyle" changes in the 6 million years that separate us from a common ancestor. Specifically, two key differences are how humans and chimps perceive smells and what we eat.



A massive gene-comparison project involving two Cornell University scientists, and reported in the latest issue of the journal Science (Dec. 12, 2003), found these and many other differences in a search for evidence of accelerated evolution and positive selection in the genetic history of humans and chimps.

In the most comprehensive comparison to date of the genetic differences between two primates, the genomic analysts found evidence of positive selection in genes involved in olfaction, or the ability to sense and process information about odors. "Human and chimpanzee sequences are so similar, we were not sure that this kind of analysis would be informative," says evolutionary geneticist Andrew G. Clark, Cornell professor of molecular biology and genetics. "But we found hundreds of genes showing a pattern of sequence change consistent with adaptive evolution occurring in human ancestors." Those genes are involved in the sense of smell, in digestion, in long-bone growth, in hairiness and in hearing. "It is a treasure-trove of ideas to test by more careful comparison of human and chimpanzee development and physiology," Clark says.


The DNA sequencing of the chimpanzee was performed by Celera Genomics, in Rockville, Md., as part of a larger study of human variation headed by company researchers Michele Cargill and Mark Adams.

Celera generated some 18 million DNA sequence "reads," or about two-thirds as many as were required for the first sequencing of the human genome. Statistical modeling and computation was done by Clark and by Rasmus Nielsen, a Cornell assistant professor of biological statistics and computational biology. Some of the analysis, which also compared the mouse genome, used the supercomputer cluster at the Cornell Theory Center. Clark explains, "By lining up the human and chimpanzee gene sequences with those of the mouse, we thought we might be able to find genes that are evolving especially quickly in humans. In a sense, this method asks: What are the genes that make us human? Or rather, what genes were selected by natural selection to result in differences between humans and chimps?" The study started with almost 23,000 genes, but this number fell to 7,645 because of the need to be sure that the right human, chimp and mouse genes were aligned.

According to Clark, all mammals have an extensive repertoire of olfactory receptors, genes that allow specific recognition of the smell of different substances. "The signature of positive selection is very strong in both humans and chimps for tuning the sense of smell, probably because of its importance in finding food and perhaps mates," says Clark. In addition to the great departure in smell perception, differences in amino acid metabolism also seem to affect chimps’ and humans’ abilities to digest dietary protein and could date back to the time when early humans began eating more meat, Clark speculates. Anthropologists believe that this occurred around 2 million years ago, in concert with a major climate change.

"This study also gives tantalizing clues to an even more complex difference -- the ability to speak and understand language," Clark says. "Perhaps some of the genes that enable humans to understand speech work not only in the brain, but also are involved in hearing." Evidence for this came from a particularly strong sign of selection acting on the gene that codes for an obscure protein in the tectorial membrane of the inner ear. One form of congenital deafness in humans is caused by mutations to this gene, called alpha tectorin.

Mutations in alpha tectorin result in poor frequency response of the ear, making it hard to understand speech. "It’s something like replacing the soundboard of a Stradivarius violin with a piece of plywood," Clark notes. The large divergence between humans and chimps in alpha tectorin, he says, could imply that humans needed to tune the protein for specific attributes of their sense of hearing. This leads Clark to wonder whether one of the difficulties in training chimpanzees to understand human speech is that their hearing is not quite up to the task. Although studies of chimpanzee hearing have been done, detailed tests of their transient response have not been carried out.

Clark emphasizes that a study like this cannot prove that the biology of humans and chimps differ because of this or that particular gene. "But it generates many hypotheses that can be tested to yield insight into exactly why only 1 percent in DNA sequence difference makes us such different beasts," he says.

Also collaborating in the study were researchers at Applied Biosystems (Foster City, Calif.), Celera Diagnostics (Alameda, Calif.) and Case Western Reserve University in Cleveland. The Science report is titled, "Inferring non-neutral evolution from human-chimp-mouse orthologous gene trios."

Roger Segelken | Cornell News
Further information:
http://www.news.cornell.edu/releases/Dec03/chimp.life.hrs.html

More articles from Life Sciences:

nachricht New technique for in-cell distance determination
19.03.2019 | Universität Konstanz

nachricht Dalian Coherent Light Source reveals hydroxyl super rotors from water photochemistry
19.03.2019 | Chinese Academy of Sciences Headquarters

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

Im Focus: Revealing the secret of the vacuum for the first time

New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum

For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...

Im Focus: Sussex scientists one step closer to a clock that could replace GPS and Galileo

Physicists in the EPic Lab at University of Sussex make crucial development in global race to develop a portable atomic clock

Scientists in the Emergent Photonics Lab (EPic Lab) at the University of Sussex have made a breakthrough to a crucial element of an atomic clock - devices...

Im Focus: Sensing shakes

A new way to sense earthquakes could help improve early warning systems

Every year earthquakes worldwide claim hundreds or even thousands of lives. Forewarning allows people to head for safety and a matter of seconds could spell...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Levitating objects with light

19.03.2019 | Physics and Astronomy

New technique for in-cell distance determination

19.03.2019 | Life Sciences

Stellar cartography

19.03.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>