Chimp genetic code opens human frontiers

Alan Boyle Science editor • Profile • E-mail

Scientists unleashed a torrent of studies comparing the genetic coding for humans and chimpanzees on Wednesday, reporting that 96 percent of our DNA sequences are identical. Even more intriguingly, the other 4 percent appears to contain clues to how we became different from our closest relatives in the animal kingdom, they said.

"We're really looking at an individual evolutionary event, and this is spectacular," said University of Washington geneticist Robert Waterston, senior author of a study in the journal Nature presenting the draft of the chimpanzee genome.

The achievement should lead to discoveries with implications for human health, including new approaches to treating age-old diseases, said Francis Collins, director of the National Human Genome Research Institute.

"As we build upon the foundation laid by the Human Genome Project, it's become clear that comparing the human genome with the genomes of other organisms is an enormously powerful tool for understanding our own biology," he said in a written statement.

The chimpanzee genetic blueprint is the result of a multimillion-dollar effort involving 67 researchers from the United States, Israel, Italy, Germany and Spain. In addition to that blueprint, more than a dozen other related reports are being published this week in Nature and two other scientific journals, Science and Genome Research.

Among the highlights from the analyses:

• Small but crucial differences: The researchers said the results confirmed the common evolutionary origin of humans and chimpanzees. Out of the 3 billion base pairs in the DNA coding for chimps and humans, about 35 million show single-base differences, and another 5 million DNA sites are different because of insertions or deletions of genetic code. Waterston estimated that 1 million of those coding changes are responsible for the functional differences between humans and chimps — thus defining our humanness.
• Six new genetic frontiers: Scientists identified six regions of our DNA that appear to have evolved dramatically over the past 250,000 years — including a "gene desert" that may play a role in nervous system development and also has been linked to obesity. They said a seventh region that showed notable change contains the FOXP2 gene, which already has been linked to speech in humans.
• Brain genes key: A comparison of gene expression in various tissues indicated that most of the genetic changes occurring during the evolution of chimps and humans had neither a positive nor a negative effect. However, the testes in the males of both species showed strong evidence of a positive effect. Also, genes active in the brain showed much more accumulated change in humans than in chimps — suggesting that those genes played a special role in human evolution.
• Primates' risky business: Scientists compared the chimp and human genomes with those of mice and rats, and found that both primates carried a greater amount of potentially harmful genetic coding. They speculated that such coding may have made primates more prone to genetic diseases, but also more adaptable to environmental changes.
• Clues to diseases: The genomes contained hints that the chimpanzee genetic code has been attacked more frequently than humans by retroviral elements — such as those present in the HIV virus. Scientists also noted key differences between the genomes that may affect susceptibility to viruses, the workings of the immune system and the progression of diabetes and Alzheimer's disease in humans.

The researchers emphasized that the studies raised more questions than answers, and that it would take years to decipher the meaning behind differences in genetic coding.

For example, although six new regions of rapid evolutionary change have been identified, "we don't know what natural selection in these regions acted upon," said Tarjei Mikkelsen, a graduate student at the Massachusetts Institute of Technology who was the first listed author for the chimp genome study.

But Waterston said the "really big picture" is that geneticists can now focus on the small percentage of DNA coding that is peculiar to humans, and figure out how that coding works.

"We're probably down to a million or so changes in the human genome that are even candidates for being the changes that have made us human," he told MSNBC.com. "So it's fun and exciting to be looking at nature's lab notebook like this."

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