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Scientists also mapped more than 4 million sites where proteins bind to DNA to regulate genetic function, sort of like a switch. “We are finding way more switches than we were expecting,” Birney said.

The discovery of so many switches may help scientists in their search for the biology of disease, particularly common conditions such as high blood pressure, heart disease and asthma, scientists said.

Studies have found that DNA variations that predispose people to such common disease often lie outside the genes, raising the question of how they could have any effect. The new work finds evidence that many of these variations fall within or near regulatory regions identified by the ENCODE project, suggesting a way they could meddle with gene activity.

Another finding raises questions about just how best to define a gene, researcher Thomas Gingeras of the Cold Spring Harbor Laboratory in New York and colleagues suggest in their report in the journal Nature. The common notion that genes are specific regions of DNA that are separated from other genes “is simply not true,” he said.

He and colleagues said it would make more sense to define a gene as a collection of RNA molecules instead of a particular location on the DNA.

Birney said that with the finding of widespread activity across a person’s DNA, scientists will be debating how much of it is really crucial to life.

Still, “it’s worth reminding ourselves that we are very, very complex machines,” Birney said. “It shouldn’t be so surprising that the instruction manual is really pretty fearsomely complicated.”

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Online:

Journal Nature: http://www.nature.com/nature