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Thursday, May 27, 2004
An international team of scientists, seeking to track the course of human evolution and the ancient roots of genetic diseases, has completed the first highly accurate map of the genes in a single chimpanzee chromosome and compared them gene-by-gene with their human counterparts.The result, the scientists say, reveals surprising differences between the species, even though they are the closest of relatives in the primate family.
The international team completed the first sequence of the genes in chimp chromosome pair No. 22, one of 24 chromosome pairs in the chimpanzee. That pair is the counterpart of chromosome 21 in the human array of 23 chromosome pairs.
The sequencing feat was accomplished by a consortium of scientists working at genetics centers in five nations headed by Yoshiyuki Sakaki and Asao Fujiyama of Japan's Genomics Sciences Center in Yokohama.
The group's report, with 45 co-authors representing hundreds of geneticists and technicians, is being published today in the scientific journal Nature.
Within a month or two, an American research consortium is expected to announce completion of the most accurate map of the entire chimp genome.
Chimp chromosome 22 contains 33.3 million chemical DNA units, known as bases. The report describes how they painstakingly determined the sequences of the DNA units with accuracy better than 99.99 percent. As the team compared the chimp DNA with the genetic material in human chromosome 21, the scientists found to their surprise that both species had both gained and lost thousands of stretches of DNA, although what caused those changes and what effect they might have had remain a mystery, they said.
Much of the work's value lies in providing clues to the nature and timing of the divergent evolution of the chimp and human lineages, according to Robert Waterston of the University of Washington, a leader in the completion of the Human Genome Project.
Despite their close relationship, chimps and humans vary greatly in their susceptibility to diseases and in their cognitive and language skills. The answers to when and how those differences arose should lie in the changes in their genes.
The chimp gene group was particularly interested in this chromosome, Sasaki said, because an extra copy of the human analogue, chromosome 21, is the cause of Down syndrome. Symptoms of Down syndrome have been reported in chimps, too.
E-mail David Perlman at email@example.com.
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