( A study comparing the genomes of both h...)Big differences in duplicated DNA distinguish chimp and human genomes

A study comparing the genomes of both humans and chimpanzees has found that much of the genetic difference between the two species came about in events called segmental duplications, in which segments of genetic code are copied many times in the genome. The study appears as a companion article to the draft sequence of the chimpanzee genome published in the Sept. 1 issue of the journal Nature.

Dr. Evan Eichler, associate professor of genome sciences at the University of Washington in Seattle, led this study, in addition to being involved in the Chimpanzee Genome Sequencing Project. Eichler, a Howard Hughes Medical Institute investigator, and his colleagues studied the chimp genome, looking for large-scale segmental duplications that consist of as many as 20,000 base pairs. They found that most of the change to the overall genome landscape between chimps and humans can be attributed to large segmental duplications. Such large-scale genetic events have altered more total base pairs - about 2.7 percent of the genome - than differences from single base-pair changes, which account for about 1.2 percent of the genome.

"For all the talk of the 1.2 percent single base-pair difference and the importance of those, there's even more difference between the species due to duplication events," said Eichler. "Now we need to learn the role of those duplication events in species evolution and disease."

The researchers divided the duplications into three groups: those found in the chimp but not the human, those found in the human but not the chimp, and those found in both species. Among the human-only duplications, some of those sections of the genome are implicated in human developmental disorders such as spinal muscular atrophy and Prader-Willi syndrome. Parts of those duplicated segments have only single copies in the chimp genome, and it is possible that the chimpanzee is therefore not predisposed to the same diseases as a human.

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Source:University of Washington

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