22: Proteins Make the Primate

By Chris Jozefowicz|Monday, January 03, 2005

Scientists uncovered subtle clues this year suggesting that chimpanzees and humans, estimated to be more than 98 percent identical in their DNA sequences, may be more different at the molecular level than previously thought. Instead of being distinguished by a small number of crucial genes, as some geneticists had supposed, the two species appear to have surprisingly significant and widespread differences in the proteins produced by their genes.

A group of international researchers completed the first highly detailed map of a single chimpanzee chromosome and matched it with its human counterpart. Among the portions that lined up, only 1.4 percent of the chemical letters were different, consistent with expectations. However, the researchers found 68,000 small discrepancies where DNA had either been added or lost on the respective chromosomes. And when they analyzed the sequences of 231 genes, they predicted that 83 percent of them would produce proteins that differed in some way.

If such discrepancies occur throughout the rest of the human and chimp genomes, there will probably be thousands of proteins that differentiate the two species. But determining which specific genetic changes led to humans won’t be easy, says Asao Fujiyama, of RIKEN Genomic Sciences Center and the National Institute of Informatics in Japan, one of the project leaders: “The key proteins are very difficult to iron out because we have so many differences.”

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