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Genome Comparison: Smell, Hearing May Separate Humans from Chimps

NEW YORK, Dec. 22 (GenomeWeb News) - With chimp sequence in hand, researchers at Cornell have begun to sort out what separates this species genomically from its closest relative in the opposable thumb club, the human.


In this genomic comparison, published in the Dec. 12 issue of Science, researchers reported that they found differences in genes that were involved in olfaction, and evidence of positive selection in these genes in humans, as well as those involved in digestion, long-bone growth, hairiness, and hearing.


"Human and chimpanzee sequences are so similar, we were not sure that this kind of analysis would be informative," evolutionary geneticist Andrew Clark, a professor of molecular biology and genetics at Cornell who led the research, said in a statement. "But we found hundreds of genes showing a pattern of sequence change consistent with adaptive evolution occurring in human ancestors."


Clark's analysis was based not on the draft of the chimp genome released Dec. 10 by the National Human Genome Research Institute, but a project to sequence 18 million reads performed by Celera Genomics as part of a study headed by Mark Adams and Michele Cargill.


Clark and Rasmus Nielsen, an assistant professor of biological statistics and computational biology at Cornell, performed the computational analysis. In addition to comparing the chimp sequence to the human, they also compared it to that of the mouse.


"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?," Clark said.


The researchers additionally found evidence that selection has acted on the gene that codes for a protein in the tectorial membrane of the inner ear, alpha tectorin. Mutations in this gene lead to a form of congenital deafness in humans.


"Perhaps some of the genes that enable humans to understand speech work not only in the brain, but also are involved in hearing," Clark said.


The Science article on the study is entitled, "Inferring non-neutral evolution from human-chimp-mouse orthologous gene trios."

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