Human chromosomes show startling similarity to birds'

Study compares sequence with chickens and mice

November 26, 1999|By KNIGHT RIDDER/TRIBUNE

PHILADELPHIA -- Scientists at Scotland's Roslin Institute, the laboratory famous for cloning Dolly the sheep, have come out with this new finding just in time for the Thanksgiving weekend: We're more like turkeys than previously believed.

The similarity -- identified specifically in chickens but present in turkeys and all other birds -- is in the way that genes are arranged on the chromosomes.

"We find that the human is more like the chicken than the human is like the mouse," said lead researcher David Burt, whose paper appeared in yesterday's issue of the journal Nature.

That's not to say that humans are closer kin of chickens -- they're birds after all, while both mice and men fall into the class known as mammalia. The human lineage branched off from the chicken lineage 300 million years ago, while we split from mice just 100 million years ago.

So the finding came as a surprise. "You'd expect the arrangement of genes to be very similar in two related species, such as two mammals," said Burt.

But there are two ways to look at an animal's genes. You can look at the genes themselves, or you can look at the order in which an animal's several hundred thousand genes are strung together on structures called chromosomes.

If genes are words, then we share more common spellings with the mouse vocabulary than we do with the chicken. But the sentences formed from their order in the chromosome look more like those of the chicken.

Somehow the mouse's genes have gotten scrambled.

Mice have managed to diverge quickly over the past tens of millions of years, their genes getting reshuffled much faster than those of humans or birds. Some of that comes from the fast turnover of mouse generations -- they breed and die over a period of less than two years.

Rapid swings in mouse populations also can cause random rearrangements of genes to spread through the whole population.

Why does it matter?

People need to look to other animals to make any sense out of the $3 billion Human Genome Project, which will tell us what our 100,000 genes look like but not what they do.

"We might know what 10,000 do, and for the other 90,000, you won't have a clue," said Burt. By looking at how some genes work in the development of chickens, which are easy to study, researchers might learn what their function is in us.

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