For the first time ever, mitochondrial DNA from shed cat hair was accepted as evidence in a U.S. legal proceeding and helped to convict a suspect of murder.
The case, which will be outlined in the November issue of the Journal Forensic Science International: Genetics, could set a precedent, such that pet hair may be more commonly introduced as evidence in U.S. trials.
“Dog hair has been used in both state and federal courts,” co-author Beth Wictum told Discovery News. “Cases range from animal theft to animal cruelty, murder, sexual assault, bestiality, and pretty much anything you can think of.”
Wictum, who is associate director of the Veterinary Genetics Laboratory Forensics Unit at the University of California at Davis, and her colleagues analyzed the single light orange-colored cat hair that was found in one of the victim’s jean pockets. The individual, from Clay County, Missouri, was found severely beaten with his throat violently lacerated to near decapitation.
Both the victim and the primary suspect lived with cats, so the cat hair by itself did not mean much, given how frequently felines shed. As any cat owner knows, strands of cat fur seem to wind up everywhere. Prior studies have demonstrated how shed cat hair can cling to everything from curtains to clothing.
The researchers therefore obtained and sequenced mitochondrial DNA (mtDNA) from the single hair. This is a type of DNA that passes down from mothers to their offspring. Another type of DNA, nuclear, provides more information because it encodes for the majority of the individual’s genome.
“Shed hair usually doesn’t have nuclear DNA because it is in the hair follicle, so we test the mtDNA in the hair shaft,” Wictum explained. “However, because cats and dogs groom themselves, we sometimes get nuclear DNA profiles from shed pet hair.”
For this case, only the mtDNA was available, but the researchers were able to compare and contrast it with mtDNA from a large general database as well as from samples of fur obtained from both the victim’s and the suspect’s cats. That was quite a challenge, since the suspect lived with 11 cats, and 8 of those were reported to be related.
The murder trial of the State of Missouri versus Henry L. Polk, Jr. represents the first legal proceeding where cat mitochondrial DNA analysis was introduced into evidence. The mitochondrial DNA evidence was initially considered inadmissible due to concerns about the cat dataset and the scientific acceptance of the marker. Those concerns were subsequently addressed, and the evidence was deemed admissible.
Source: Discovery News