The Eye Opener

DNA Varies More Widely From Person to Person, Genetic Maps Reveal

National Geographic News

November 22, 2006

The genetic makeup of the human race is much more varied than previously believed, new research shows.

Scientists say that surprisingly many large chunks of human DNA differ among individuals and ethnic groups.

The research also suggests that humans have less DNA in common with chimpanzees, our closest living relative, than is widely supposed.

The new findings, based on several studies, will have dramatic implications for research into deadly diseases, the researchers add.

In the lead study, reported tomorrow in the journal Nature, scientists created the first map of the human genome that shows that large segments of DNA are missing or duplicated between normal, healthy people.

Known as copy number variants (CNVs), some of these altered DNA sequences can be responsible for increased susceptibility to cancers and many other diseases, the study team says.

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"One can no longer consider human traits as resulting primarily from single base pair changes," he said. "This is perhaps the most important breakthrough in human and medical genetics in several decades.

"I would say it rivals finally knowing the number of chromosomes [50 years ago] that makes us humans and showing that some syndromes can result from an abnormal number of chromosomes."

Disease Breakthrough?

The study team says their genome map will provide new ways for scientists to identify genes involved in disease.

Many examples of diseases known to result from changes in DNA copy number are emerging, the team points out.

Yet current tests for mutated genes that cause diseases won't detect most CNVs, the researchers warn.

CNVs revealed in the study are associated with a wide variety of diseases, including AIDS, cataracts, heart disease, and schizophrenia.
"Medical research will benefit enormously from this map," team member Lee said.

The study also highlighted genetic differences among the population groups tested, with 11 percent of copy number variations not being shared between people of European, African, and East Asian ancestry.

Some of these differences may relate to how different ethnic groups adapted to their specific environments, according to Hurles of the Wellcome Trust Sanger Institute.

For instance, he says, the African group was found to have higher copy numbers of a gene associated with increased resistance to HIV infection.

The team says an understanding of how such genetic variation is distributed around the world can reveal much about human prehistory and help in tracking down disease genes.

The findings also suggest "more genetic variation between human genomes and chimpanzee genomes than we had previously appreciated," Lee said.

Past studies suggest chimps share around 99 percent of their DNA with humans.

"If you add on CNVs, you do see a lot more differences between the two species," Lee added.

The researchers say their findings suggest a figure in the region of 96 to 97 percent similarity.

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