v. related to plight + deconvolution
QT:{{”
Dr Willerslev had been able to obtain SNPs from Meng’s trousers. Then came the task of trying to identify whom they could have come from. In 2023 a man called Philip Patrick Westh was arrested in connection with a kidnapping case in the same area; because of similarities between the cases, the police believed that he had killed Meng too (Mr Westh denies most of the accusations related to the kidnapping case and pleaded not guilty to the charge of killing Meng). To assess the probability that the genetic material from Meng’s trousers had come from Mr Westh, Dr Willerslev made use of a DNA database of ordinary, healthy Danes. If the SNPs found on the trousers were identical to those in Mr Westh’s DNA, went the logic, and enough of them were sufficiently rare variants, the probability that they did indeed come from Mr Westh went up. Dr Willerslev testified that this particular pattern of SNP variants would be at least one million times more likely to turn up if the sample included DNA from Mr Westh, or a close relative, than if it did not.
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But identifying a suspect from SNPs is another matter. Degraded samples can be extremely complex to analyse, says Dr Simonsen, in particular if material from several people has been mixed together. There are no standardised forensic protocols for separating out those signals, nor for how to confidently calculate the probability that the DNA belongs to a suspect. That matters because the stakes are somewhat higher in a criminal case than in the study of mammoths and dodos. But, says Dr Simonsen, “We expect that nut to be cracked.” He hopes to learn from Dr Willerslev’s team and develop new forensic tools. The work has already started: in September, researchers from Aalborg University and the University of Copenhagen, with whom he
collaborates, published a paper describing an approach for doing identification calculations based on SNPs.
He is not the only one to see potential. An American company called Astrea Forensics has recently spun out from the palaeogenomics group at the University of California in Santa Cruz, to offer aDNA expertise to law enforcement. Their speciality is the nuclear DNA found within hair, which has long been considered too fragmented and scarce to be of any use.
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