Study: Humans’ DNA Not Quite So Similar

Malcolm Ritter, AP, September 3, 2007

People are less alike than scientists had thought when it comes to the billions of building blocks that make up each individual’s DNA, according to a new analysis.

“Instead of 99.9 percent identical, maybe we’re only 99 percent (alike),” said J. Craig Venter, an author of the study—and the person whose DNA was analyzed for it.

Several previous studies have argued for lowering the 99.9 percent estimate. Venter says this new analysis “proves the point.”

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The order of building blocks along a strand of DNA encodes genetic information, somewhat like the way a sequence of letters creates a sentence. Particular sequences form genes. Landmark studies published in 2001 indicated that the DNA of any two people is about 99.9 percent alike. The new paper suggests estimates of 99.5 percent to just 99 percent, Venter said.

The Venter paper joins several others published over the past three to four years that indicate an estimate of around 99 percent, said Richard Gibbs, a DNA expert at the Baylor College of Medicine in Houston who didn’t participate in Venter’s study.

The studies produce the lower figure because they uncovered chunks of DNA that differ among people, whereas previous studies focused on differences in individual building blocks.

The 99 percent figure is close to what scientists have often estimated for the similarity between humans and chimps. But the human-chimp similarity drops to more like 95 percent when the more recently discovered kinds of DNA variation are considered, Venter said.

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That finding in turn is shedding light on how DNA varies among people, with implications for understanding the genetic underpinnings of disease, Gibbs said.

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Initial study of genome entrepreneur Craig Venter’s own DNA map shows 4.1 million places where his genetic code is different from the basic “reference” human genome.

This is many more than had been expected, including big differences that extend far beyond the single-letter changes that account for much of the variation seen so far.

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“I found out that I have a high probability of having blue eyes,” the blue-eyed Venter said in a telephone interview.

“You can’t even tell with 100 percent accuracy if I would have blue eyes, looking at my genetic code,” he laughed. “We all thought that would be simple.”

The researchers at the J. Craig Venter Institute in Maryland, along with teams at The Hospital for Sick Children in Toronto and the University of California San Diego, analyzed Venter’s genetic code to compare it with the rival human genome maps published in 2001 by Venter’s private company and the publicly funded Human Genome Project.

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Writing in the Public Library of Science journal PLoS Biology, the researchers said it would also be useful as a rare exercise to thoroughly examine a single person’s genome and compare it to these averages.

DISPELLING FEAR

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Both Venter and [James] Watson have said they wanted to serve as examples to a public often afraid of genetic sequencing, in part for fear of being denied jobs or insurance coverage and in part because of privacy concerns.

One thing the researchers wanted to find was if an individual’s risk for disease could be discerned just by looking at his or her genes.

Only for a few illnesses is this a certainty. Huntington’s disease is one—if a person carries the mutated Huntington’s gene, he or she will develop the deadly and incurable disease.

But most other diseases are the result of a more complex interaction between genes and environment.

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Venter has versions of three genes believed to lower the risk of heart disease and carries two copies of a gene mutation that raise the risk of a heart attack, the study found.

Venter said he started taking a cholesterol-lowering statin drug years ago, even though his cholesterol levels were below those recommended for taking such medications.

“I don’t have to have a 100 percent chance of heart disease to think of taking preventative measures,” Venter said.

His mother is 84 and still active, he noted.

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