03 May 2011

Bin Laden's DNA

For the second day in a row, The Plain Dealer, Cleveland's main newspaper, devoted its first page to coverage of the tracking down and killing of Osama Bin Laden. As I scanned the front page of today's (Tuesday, May 3, 2011) edition, I was attracted to one headline among the list of articles inside: "A DNA Match. Details on page A9." I immediately turned to this article inside the 10 pages of "special coverage" to see what I could learn about DNA testing. There were several facts new to me.

In the balance of this post, I am including most of that article by two Associated Press reporters because of its focus on the use of DNA in confirming the identity of bin Laden. The text below from www.Cleveland.com, the PD's website, differs slightly from the version in the paper. Comments by me are included in square brackets.

DNA testing confirms Osama bin Laden death, sources say

WASHINGTON — The U.S. used multiple means to confirm the identity of Osama bin Laden during and after the firefight in which he was killed, before placing his body in the North Arabian Sea from aboard a U.S. aircraft carrier, senior U.S. officials said Monday.
The al-Qaida leader was identified by name by a woman believed to be one of his wives — bin Laden had several — who was present at his Pakistan compound at the time of the U.S. raid. He also was visually identified by members of the U.S. raid squad, a senior intelligence official told reporters at a Pentagon briefing. Under ground rules set by the Pentagon, the intelligence official and two senior defense officials could not be identified by name.
The intelligence official said the DNA match, using DNA from several family members, provided virtual certainty that it was bin Laden's body. The U.S. is believed to have collected DNA samples from bin Laden family members in the years since the 9/11 attacks that triggered the U.S.-led invasion of Afghanistan. It was unclear whether the U.S. also had fingerprints or some other means to identify the body on site.
U.S. officials also said bin Laden was identified through "facial recognition," a reference to technology for mapping unique facial characteristics, but it was not clear exactly how the Navy SEAL troops performed the comparison.
Positive identification of the remains is considered a critically important part of the U.S. operation, given the symbolic importance of bin Laden's leadership of the Islamic extremist movement that was based in Afghanistan until the U.S. invaded in October 2001.
Officials did not immediately say where or how the testing was done but the test explains why President Barack Obama was confident to announce the death to the world Sunday night. Obama provided no details on the identification process.
Dr. Bruce Budowle, a former senior scientist at the FBI, said DNA confirmation can be achieved quickly under the right circumstances.
Budowle, currently director of the Institute of Investigative Genetics at the University of North Texas Health Science Center at Fort Worth, said using a sample of blood or a cheek swab, "you extract the DNA that day, get the PCR done in the same day, put it on the machine that night... and interpret it the following day." PCR, or polymerase chain reaction, technology allows scientists to rapidly copy a single stretch of DNA using cycles of heating and cooling. Then it's a matter of adding fluorescent dyes to compare specific spots on that chunk of DNA with the relative's sample.
If markers on standard, well-known regions match, they have a positive identification.
[As noted, the foregoing was taken from Cleveland.com. The following was included in the PD's article, and I add it here because it's interest to genealogists.]
DNA matching usually involves obtaining material from a blood sample or cheek swab. The vast majority of a person's DNA sequence will be the same as every other person's. So a test, which can be done in a few hours if needed, focuses on a small number of locations on the genome, usually 13 to 16 spots.
These spots are on what is sometimes referred to as junk DNA areas of genetic material that do not contain instructions for building brain, bone, or muscle. A DNA analysis looks for patterns of two or more nucleotides, the chemicals that form DNA.
These strings of nucleotides are called short tandem repeats. The closer the relative, the more that pattern of repeats matches. In an identical twin, they should be the same.
A parent and child should share half the number of repeats. In siblings, the combinations can vary;  in half-siblings, they can vary even more.
"With a sibling, there is only a likelihood that you'll share some DNA with them," said Mitchell Holland, a forensic scientist at Penn State and former head of the Armed Forces DNA Identification Laboratory. "With a half-sibling, that complicates things even further."
Bin Laden did not have any full siblings. He did have more than 50 half-siblings, some of whom have close ties to the United States and had long ago distanced themselves from him. Using a half-sibling's DNA could still yield a resonably high chance of identification, more than 90 percent. And collecting DNA from several half-siblings would increase the likelihood of making a match.
"If you have that, you can attempt to reconstruct the parents," Holland said. "You know the numbers the proof is coming from. But the math is relatively complex."

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