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Tuesday, February 1, 2011

Orangutan genome yields surprises

An international team of scientists has sequenced the genomes of both Sumatran and Bornean orangutans. This new data brought up as many mysteries than it solved.


Divergence among great apes, a small ape, and an Old World monkey with respect to humans.

Divergence among great apes, a small ape, and an Old World monkey with respect to humans.

On the one hand, compared to the other great apes, orangutans have extraordinarily stable genomes. Structurally, orangutan DNA has undergone far fewer major events like duplications and translocations. This may be due in part to a lack of repetitive elements such as ‘Alu’. This 300 base pair long bit of DNA pops up throughout our genomes and is thought to be a driving force of genetic mutation and rearrangement. Humans have about a million Alu repeats making up 10% of our genomes. About 5000 of these Alu elements are human-specific. That means that in the 5 million or so years since chimps and humans diverged, the human genome gained 5000 Alu repeats. In contrast, over the past 15 million years, orangutans only gained 250 Alu repeats.

Meanwhile, the two types of orangutans, Bornean and Sumatran, diverged 400,000 years ago. Despite its structural stability, the orangutan genome is much more diverse than that of humans. Surprisingly, there was greater variety among Sumatran orangutans, even though they are outnumbered seven to one by their Bornean cousins.

To sum up: orangutans have extremely diverse genomes that have not changed structurally in the past fifteen million years. To put that time frame in perspective, humans have existed in our current form for only about 200,000 years.