Thursday, August 19, 2010

Junk DNA and copy number variation

Wow, amazing genomic phenomena described in this new research: an explicit demonstration of the impact of copy number variation, and "dead" junk DNA revitalized by a mutation!

NYTimes: The human genome is riddled with dead genes, fossils of a sort, dating back hundreds of thousands of years — the genome’s equivalent of an attic full of broken and useless junk.

Some of those genes, surprised geneticists reported Thursday, can rise from the dead like zombies, waking up to cause one of the most common forms of muscular dystrophy. This is the first time, geneticists say, that they have seen a dead gene come back to life and cause a disease.

... As they studied the repeated, but dead, gene, Dr. Tapscott and his colleagues realized that it was not completely inactive. It is always transcribed — copied by the cell as a first step to making a protein. But the transcriptions were faulty, disintegrating right away. They were missing a crucial section, called a poly (A) sequence, needed to stabilize them.

When a mutation added back this sequence, the dead gene came back to life. “It’s an if and only if,” Dr. Housman said. “You have to have 10 copies or fewer. And you have to have poly (A). Either one is not enough.”

But why would people be protected if they have more than 10 copies of the dead gene? Researchers say that those extra copies change the chromosome’s structure, shutting off the whole region so it cannot be used. ...

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