On junk DNA

While we talk about the quirks of DNA and mutations in class this week, here's a good review of junk DNA that you might enjoy spending a few minutes reading. Here's how it begins:

The instructions for "life as we know it" are coded in DNA, but it appears that only a fraction of our DNA is ever used. (This is probably not true of our brains, myths notwithstanding.) At least, only a fraction of it is ever translated into proteins such as enzymes. Some of the untranslated (noncoding) DNA has known functions, such as coding for the RNA part of the ribosomes that translate messenger RNA into protein, but much appears to be junk. Much of the junk is multiple copies of transposons, bits of unusually selfish DNA that reproduce like rabbits and burrow into the chromosomes, sometimes presumably disrupting functional DNA.

But if the noncoding DNA is mostly useless junk, why has some of it apparently been preserved by natural selection?

Go read the whole thing on This Week in Evolution, a blog I hope is becoming part of your weekly wander through the blogosphere.