Thursday, August 16, 2007

In evolutions playground, Humans left chimps behind

What is the difference between humans and chimps?
MICRO-RNA, the snippets of RNA that control gene expression, could be the difference.

Variation between individuals, in traits ranging from pigment to behaviour, is the raw material of evolution. The difference can be down to very subtle changes: the genes involved may code for exactly the same proteins but make them at other places and times. So could micro-RNA be the determining factor?

What do Micro-RNA's do?
Micro-RNAs are a mere 22 nucleotides long and block the messenger RNA that translates DNA into protein. This allows them to fine-tune gene expression. Micro-RNA has only recently been studied because it was discovered withing the last few years. But it has been shown to determine what cell types form, and, for example, whether sheep become muscular or puny.

Now, researchers at the Hubrecht Laboratory in Utrecht, the Netherlands, have combed painstakingly through the RNA in human and chimp brains, and found 447 new micro-RNAs, more than doubling the number discovered so far. Some were expressed very rarely.

What accounts for the differences between Chimps and Humans?
The brain has 10,000 cell types, so it is possible because of all these micro-RNAs. Many were unique to chimps and humans, and some only to humans. So while we share most of our DNA with chimps, the small genetic changes through Micro RNA that fine-tune its expression might account for the radical differences in our brains. This is the playground of evolution.

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