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Low Copy Forensics

Low copy number DNA analysis can enable researchers to generate genetic profiles from fossils that are thousands of years old, but its use in forensics is a bit more fraught, the New York Times reports.

Washington State University's Brian Kemp, who studies DNA from 10,000-year-old fish, tells the Times that "[w]e can be down to 10 or 20 molecules."

But with the ability to detect such small amounts of DNA, the risk of contamination and distorted results rises, and in forensics, those implications could affect cases.

First of all, the Times notes that it can be harder to link those tiny amounts of DNA to the crime itself, as it could have been left behind at a different time.

"Maybe there's not three people bleeding on a steering wheel, but there are three people touching it," Kirk Lohmueller from the University of California, Los Angeles, tells the paper. "Before, you didn't have to worry about that."

In addition, low copy number DNA analysis can push PCR past its limits so that nothing is amplified and it can suffer from allelic dropout. This may led forensic scientists to come to incorrect conclusions, the Times writes.

"I'm not pleased with what's been done with low copy number in forensics to date," Bruce Budowle from the University of North Texas Health Science Center tells the Times.

He served as an expert witness for the defense in a murder trial that relied on DNA evidence from a bicycle handle, and he questioned the way the allelic dropout rate was calculated. He does, though, use the approach in his own research to identify Civil War and other remains.

"But if we get better interpretation, I think it could be a better system," Budowle adds.

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