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From Junk to Function and Back Again

The human genome is some 3.2 billion bases large, writes Carl Zimmer in the New York Times Magazine, and is dwarfed by the onion genome as well as broad-footed salamander, the African lungfish, and more. But, Zimmer adds, these organisms don't seem to be any more complex than people are. So, he asks, what is all that DNA doing?

According to the University of Guelph's T. Ryan Gregory, the answer is not much, Zimmer says. Gregory and some others say that while some noncoding DNA likely has essential function, the bulk of it is extra baggage.

The idea that much of the genome is 'junk DNA' has been around since the 1970s, Zimmer writes. Proponents of this idea argue that that some stretches of junk DNA used to be genes but mutations rendered them inactive while other regions are copies of transposable elements that have been bouncing their way around the genome.

But then, Zimmer says, opinion swung the other way as studies of the genome found functionality, some of it essential, within noncoding DNA. For instance, John Rinn, now at Harvard, has found that cells read more DNA than thought, including noncoding portions, Zimmer writes. Some of those regions produce RNA molecules that seem to be important for proper development or for bringing DNA into different configurations.

Researchers like Rinn, Zimmer adds, then think there is more to be discovered within those noncoding stretches of the genome.

At the same time, Gregory and others like him say there likely isn't much to be found. He tells Zimmer that it's like using a metal detector at beach to find gold — a fine idea as long as it doesn't respond to every bit of metal trash. "You're going to find bottle caps and nails," Gregory says.

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