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updated 1/17/2005 2:21:15 PM ET 2005-01-17T19:21:15

Researchers working in Iceland say they have identified a genetic pattern that makes some Europeans more fertile.

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The genetic pattern, known as an inversion, is a stretch of the DNA code that runs backwards in people who carry it.

Usually, such rearrangements of a chromosome are harmful to carriers. But this one causes carriers to have more children each generation — giving them what is known as a selective advantage, the researchers reported.

The finding, published in Monday’s issue of the journal Nature Genetics, opens some interesting questions about human evolution, the team at Iceland’s DeCODE Genetics said.

“We found that almost 20 percent of people in Iceland have at least one copy of this inversion,” DeCODE spokesman Edward Farmer said in a statement. “We then turned to other databases to see whether it existed elsewhere and how common it was. It turns out to be fairly common in European populations but quite rare in Africa and virtually absent in Asia.”

More than 29.000 Icelanders donated DNA samples to a database open to scientists, which DeCODE specializes in studying.

Focusing on the code's location
Genes are carried on structures known as the chromosomes. The DNA code varies from person to person, but the genes and other part of the code generally lie along the same chromosomes in the same order.

This large stretch of DNA is on chromosome 17, Augustine Kong and Kari Stefansson of DeCODE found. They are checking to see whether the inversion affects the function of the genes contained in it.

About 21 percent of all Europeans they looked at have the same inversion, which they named H2, but just 6 percent of Africans and 1 percent of Asians.

The effects of the H2 inversion are not seen on an individual level, as each carrier produces an average 0.06 more children. But across populations and generations, it adds up, the researchers said.

3-million-year-old inversion
Calculations suggest the inversion has existed for about three million years, the researchers said.

“This predates the emergence of anatomically modern Homo sapiens in Africa (150,000 years ago) and may even predate the origin of the genus Homo (2.5 million years ago),” they wrote.

It could be that the inversion has survived in the human genetic code for that long.

Or it could be that modern Homo sapiens bred with earlier species, such as Homo erectus, and inherited the genetic variation that way. The two species may have lived side by side for a time before Homo erectus went extinct, sometime between 400,000 and 50,000 years ago.

And the researchers say the inversion makes carriers more fertile. In each generation, an H2 carrier has about 3.2 percent more children than people without the sequence.

That is enough of an advantage to have “profound consequences” on evolution, Nature Genetics said.

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