This was bound happen, Dogs after all evolved and still evolving with us - here:
Police investigating the gang-related crime found a trail of blood running from the park right to Johnson's front door and suspected it belonged to the dog, which had been injured during the attack. When DNA analysis matched this blood and the blood on the victim's body to Tyson, the case was clinched. In March, Johnson was found guilty of murder - condemned by evidence from his own dog, which he had used as a weapon.
This conviction was the first to use reference samples from a new UK database of dog DNA, which opened for business earlier this year. With more cases in the pipeline, such services are clearly in demand. The US is leading the game and has several similar databases that have sprung up over the decade, and some high-profile criminal cases hingeing on animal DNA. This year, a DNA database dedicated to combating dogfighting was launched in the US (see "Busting the fight club"). Doggy forensics looks set to take off.
When investigators have only a single dog hair or the tiniest trace of canine blood to go on, there may not be enough intact genetic material to run a standard profile. Then, instead of looking for genetic markers from regular DNA, forensic scientists may have to rely on mitochondrial DNA found within the cell's power houses, which is present in far greater quantities than nuclear DNA. This approach is less reliable, since there is less genetic variation between dogs in mtDNA than in nuclear DNA. Here, forensic scientists look at the variation in the mtDNA sequence itself rather than looking at markers, but even if there is a complete sequence match there is still a reasonable chance that the mtDNA could belong to another dog.
Some sequences are so common they have a match probability of about 1 in 7. However, around a quarter of the dogs in the world have fairly uncommon mtDNA sequences; these dogs have profiles that are shared with only 1 to 5 per cent of other dogs. A further quarter have sequences that are likely to be shared by fewer than 1 per cent of dogs, making mtDNA analysis more effective. "It's kind of a roll of the dice," says Joy Halverson, director of Zoogen, an animal DNA testing company in Davis, California.
Occasionally forensic scientists find a particularly rare mtDNA profile that can make or break a case. For example, canine mtDNA helped to convict a burglar in the US who broke into a home and put the owners' two barking pekinese dogs into a lit oven. The larger dog, Dexter, managed to escape, leaving a droplet of blood on the defendant's shorts in the process. Elizabeth Wictum, who runs a dog DNA database at the University of California, Davis, worked on the case and calculated that the likelihood of the mtDNA from this droplet belonging to another dog was 1 in 100. "The actual DNA sequence was only seen in dog breeds originating in Asia - and because they were pekinese, that gave further evidence beyond statistics," she says.
Police investigating the gang-related crime found a trail of blood running from the park right to Johnson's front door and suspected it belonged to the dog, which had been injured during the attack. When DNA analysis matched this blood and the blood on the victim's body to Tyson, the case was clinched. In March, Johnson was found guilty of murder - condemned by evidence from his own dog, which he had used as a weapon.
This conviction was the first to use reference samples from a new UK database of dog DNA, which opened for business earlier this year. With more cases in the pipeline, such services are clearly in demand. The US is leading the game and has several similar databases that have sprung up over the decade, and some high-profile criminal cases hingeing on animal DNA. This year, a DNA database dedicated to combating dogfighting was launched in the US (see "Busting the fight club"). Doggy forensics looks set to take off.
When investigators have only a single dog hair or the tiniest trace of canine blood to go on, there may not be enough intact genetic material to run a standard profile. Then, instead of looking for genetic markers from regular DNA, forensic scientists may have to rely on mitochondrial DNA found within the cell's power houses, which is present in far greater quantities than nuclear DNA. This approach is less reliable, since there is less genetic variation between dogs in mtDNA than in nuclear DNA. Here, forensic scientists look at the variation in the mtDNA sequence itself rather than looking at markers, but even if there is a complete sequence match there is still a reasonable chance that the mtDNA could belong to another dog.
Some sequences are so common they have a match probability of about 1 in 7. However, around a quarter of the dogs in the world have fairly uncommon mtDNA sequences; these dogs have profiles that are shared with only 1 to 5 per cent of other dogs. A further quarter have sequences that are likely to be shared by fewer than 1 per cent of dogs, making mtDNA analysis more effective. "It's kind of a roll of the dice," says Joy Halverson, director of Zoogen, an animal DNA testing company in Davis, California.
Occasionally forensic scientists find a particularly rare mtDNA profile that can make or break a case. For example, canine mtDNA helped to convict a burglar in the US who broke into a home and put the owners' two barking pekinese dogs into a lit oven. The larger dog, Dexter, managed to escape, leaving a droplet of blood on the defendant's shorts in the process. Elizabeth Wictum, who runs a dog DNA database at the University of California, Davis, worked on the case and calculated that the likelihood of the mtDNA from this droplet belonging to another dog was 1 in 100. "The actual DNA sequence was only seen in dog breeds originating in Asia - and because they were pekinese, that gave further evidence beyond statistics," she says.
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