February 7, 2011

Orangutan Genome Sequenced

Photo of an orangutan. Yerkes National Primate Research Center.

In an international effort, researchers have decoded the orangutan genome, revealing intriguing clues about the evolution of primates, including humans.

Orangutans, known for their distinctive auburn hair, are primarily tree dwellers native to the Southeast Asian islands of Sumatra and Borneo. Of the great apes — a biological family that includes humans — orangutans are our most distant relatives, whereas chimpanzees are the most closely related. Sumatran and Bornean orangutans are both listed as endangered species by the International Union for Conservation of Nature. This can be attributed to loss of habitat, deforestation, hunting and disease.

The orangutan genome sequence comes from the DNA of a single Sumatran female. In addition to this detailed sequence, 5 Sumatran and 5 Bornean orangutan genomes were sequenced at a less detailed level. The study was funded in part by NIH’s National Human Genome Research Institute (NHGRI) and other NIH components. The results appeared in the January 27, 2011, issue of Nature.

The researchers discovered that humans and orangutans share approximately 97% of their DNA. This compares to about 99% sequence similarity between humans and chimps.

The orangutan is the third nonhuman primate to have its genome sequenced, after the chimp and rhesus macaque. Although humans and orangutans are similar at the DNA level, a comparison of the primate genome sequences revealed that orangutans have evolved much more slowly than chimpanzees and humans. The orangutan genome has fewer large DNA rearrangements than its chimpanzee and human counterparts.

"In terms of evolution, the orangutan genome is quite special among great apes in that it has been extraordinarily stable over the past 15 million years," says study coauthor Dr. Richard K. Wilson, director of the Washington University Genome Center in St. Louis. "This compares with chimpanzees and humans, both of which have experienced large-scale structural rearrangements in their DNA that may have accelerated their evolution."

One structural oddity the researchers found is called a neocentromere. Centromeres sit in the middle of chromosomes and help keep the chromosomes properly aligned during the complex process of cell division. A neocentromere is a centromere that appears in a novel location. This is the first neocentromere discovered in a primate genome. The discovery will help researchers understand how centromeres and chromosomes change and evolve.

Analysis of the 10 less detailed orangutan genomes revealed unexpected genetic diversity across and within both orangutan species. Diversity may enhance the ability of different populations to stay healthy and adapt to changes in the environment.

"The average orangutan is still more diverse — genetically speaking — than the average human," says coauthor Dr. Devin Locke of the Washington University Genome Center. "We found deep diversity in both Bornean and Sumatran orangutans, but it's unclear whether this level of diversity can be maintained in light of continued widespread deforestation of their homes."

The researchers say that, given these population variations, their genomic data will provide a valuable resource to aid in the preservation of orangutans.

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