January 25, 2011 - Among great apes, orangutans are humans’ most distant cousins. These tree dwellers sport a coat of fine reddish hair and have long been endangered in their native habitats in the rainforests of Sumatra and Borneo in Southeast Asia.
Now, a team of scientists, led by Washington University, has decoded, or sequenced, the DNA of a Sumatran orangutan. With this genome as a reference, the scientists then sequenced the genomes of five more Sumatran and five Bornean orangutans.
Their research, published in Nature, reveals intriguing clues about the evolution of great apes, including humans, and showcases the immense genetic diversity across and within Sumatran and Bornean orangutans.
Diversity is important because it enhances the ability of populations to stay healthy and adapt to changes.“The average orangutan is more diverse – genetically speaking – than the average human,” says lead author Devin Locke, a geneticist at university’s Genome Centre.
“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.”
The scientists catalogued some 13 million DNA variations in the orangutans. This valuable resource can help conservationists assess the diversity of orangutans both in the wild and in captivity.
The orangutan genome adds detail to the evolutionary tree and gives scientists insights into the unique aspects of human DNA that set man apart from the great apes, their closest relatives. Overall, the researchers found that the human and orangutan genomes are 97 per cent identical.
Slow to evolve but stable
However, in a surprising discovery, the researchers found that at least in some ways, the orangutan genome evolved more slowly than that of humans and chimpanzees, which are 99 per cent similar.
“In terms of evolution, the orangutan genome is special among apes in that it has been extraordinarily stable over the past 15 million years,” says senior author Richard Wilson, director of the Genome Centre.
“This compares with chimpanzees and humans, both of which have experienced large-scale structural changes of their genome that may have accelerated their evolution.”
The genome book
A genome reads much like an instruction book for creating and sustaining a particular species. The chromosomes are the chapters and within every chapter are paragraphs, sentences, words and single letters, which are like the individual bases of the DNA sequence.
“If you are editing a book on your computer, you can highlight a paragraph and copy and paste it, delete it or invert it,” Wilson explains. “Duplications, deletions and inversions of DNA are types of structural variations.
When we look at the genomes of humans and chimps, we see an acceleration of structural changes over the course of evolutionary history. But for whatever reason, orangutans did not participate in that acceleration, and that was a surprise.”
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