While federal officials said analysis of DNA from several relatives helped confirm that it was Osama bin Laden who was killed in the military raid on Monday, they have not yet disclosed the relationships of the family members whose DNA was used.
Officials said they collected multiple DNA samples from bin Laden's relatives in the years since the September 11 attacks. And they said the analysis, which was performed the day bin Laden was killed but after his body was buried at sea, confirmed his identity with 99.9 per cent accuracy.
Some scientific experts said if results really were so accurate, at least one of the sources was likely to have been a close relative, like a child or parent with whom he shared half his genes.
“That would be most likely,” said Frederic Zenhausern, director of the Center for Applied NanoBioscience and Medicine at University of Arizona.
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 the 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 University and former head of the Armed Forces DNA Identification Laboratory. “With a half-sibling, that complicates things even farther.”
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.
Mr. Zenhausern said using a half-sibling's DNA could still yield a reasonably high chance of identification, more than 90 per cent. And collecting DNA from several half-siblings would increase the likelihood of making a match.
Complex math
“If you have that, you can attempt to reconstruct the parents,” said Mr. Holland. “You know the numbers the proof is coming from. But the math is relatively complex.” — New York Times News Service
