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Scientists Map Entire DNA Sequence of One Person

BY Admin  September 4, 2007 at 5:30 PM EST

DNA strand

The research allows scientists for the first time to separately examine the strands of a person’s maternal and paternal DNA. It also suggests that there may be much more genetic variation between people than previously thought.

Data from two previous human genome studies, published in 2000, had suggested that humans are 99.9 percent genetically identical and that our many differences are rooted in the other 0.1 percent. The new study, however, suggests that people are only about 99.5 percent identical.

“The biggest single surprise is how much we missed the boat with the human genome seven years ago, and how different we really are,” Venter told Canada’s Globe and Mail.

Venter and his colleagues at the company Celera Genomics put together one of the two genomes sequenced in 2000, the other was assembled by a rival team of federally funded scientists led by Francis Collins.

The new study, led by Venter’s new venture, the J. Craig Venter Institute in Maryland, surpasses the earlier research in several ways.

The older studies sequenced composite genomes made up of the DNA of several people, rather than one individual. Also, those studies actually sequenced only half genomes, called “haploid” genomes. Genes are made up of bundles of DNA called chromosomes, and everyone inherits two sets of 23 chromosomes — one from a mother, and one from a father. The original studies only sequenced one of the sets, on the assumption that the two are very similar. However, the new study mapped all 46 chromosomes.

“It’s very easy to start mixing up the readouts from each parent because they are so similar,” study coauthor Samuel Levy told the New York Times.

But mapping the pieces separately may help scientists understand how interactions among maternal and paternal genes affect a person’s chance of, for example, developing a particular disease. A gene inherited from a father, for example, could predispose a person to developing the disease, while one inherited from the mother might help counteract that.

“I might want to know: Do I have an additive risk from the genomes from both my parents, or did I get some helpful ones from her that counteract the ones from him,” Venter explained to the New York Times.

In Venter’s case, 44 percent of the genes he inherited from one parent had at least slight differences from the genes he inherited from the other parent, and a third of those variations had never been seen in other people, according to the Times. These findings are what suggest that humans are more genetically variable than previously thought.

Some researchers question Venter’s decision to sequence his own DNA, especially because the outspoken scientist has been known for his showmanship.

“There is this long history of Craig’s vanity, which for much of the scientific community is irritating,” genome expert Edward Rubin of the Lawrence Berkeley National Laboratory told the New York Times.

But Venter said that using his own genome sidesteps some of the privacy concerns that using anyone else’s might have raised. He plans to make his entire genome map, along with his medical history and other information, available to researchers. The genome map suggests he has 857 genes with variants that have been linked to diseases, although it’s usually not clear exactly what role they play in actually developing the diseases. Venter said he’ll likely provide even more information to researchers who want it.

“I’m willing to do anything non-invasive,” he joked with the Globe and Mail. “But I’m not giving a brain biopsy.”

Decoding a human genome is still an expensive proposition, but it’s getting cheaper. The original human genome sequences cost nearly $3 billion. Scientists estimate that today, sequencing an entire genome could probably be done for about $100,000. And many think that in the next five years, the cost could drop to about $1,000. At that point, many people could choose to have their genome mapped.

“This is the ultimate form of genealogy,” study co-author Stephen Scherer told the Washington Post. “You’ll have incredible information about yourself.”