Nuclear DNA can provide a veritable match to a suspect, but mitochondrial DNA is a relatively new phenomenon in Canadian courts.
Known as mtDNA, it’s the genetic material found in the mitochondria of cells rather than the nucleus.
MtDNA has been used in anthropological and genealogical studies as well as after 9-11 and to examine the remains of Czar Nicholas II. Still, its use in American courts is controversial.
You inherit mtDNA maternally. Absent genetic mutations, a mother’s mtDNA passes on to her children. As a result, they have the same mtDNA as their maternal relatives.
A rootless hair may have degraded DNA that cannot yield a nuclear DNA profile. But mtDNA is available in great numbers in the cell, meaning the profile of the evidentiary sample may be available.
The mtDNA test result reveals markers or nucleotides and ultimately a profile or what’s called a haplotype. This profile is compared with those in a databank created by the FBI in the United States.
The Scientific Working Group on DNA Analysis Methods database contains 4,839 convenience samples collected in a non-random manner from FBI agents, paternity suit samples, and other sources.
The FBI database contains 1,655 Caucasians, 1,148 African-Americans, and 686 people of Hispanic descent. About half the haplotypes appear only once, but that still makes it difficult to tell if they are rare because the databank is so small.
While the profiles are publicly available, authorities restrict access to them. In fact, mistakes have occurred because information was manually inputted. As a result, only the FBI can correct these errors.
MtDNA mutates more readily than nuclear DNA. A hair from one area of your head, for example, may not have exactly the same profile as a hair from another area. This is called heteroplasmy.
If hair turns up at a crime scene and it differs by one marker from a known sample, the result is inconclusive. Authorities can neither include nor exclude the suspect.
The prosecution may put mtDNA forward as evidence to identify the accused, but the crux of the matter is that it cannot prove identity. It can only include, exclude or be inconclusive.
A powerful tool for exoneration and exclusion, mtDNA is potentially unsafe science when authorities attempt to use it to identify a suspect. Because jury members may confuse it with nuclear DNA, they require a special caution before tendering the evidence.
The American database has significant limitations. For example, French-Canadians, Inuit, and Mohawk are not in it, but the Apache and Navajo are. A defence challenge to mtDNA evidence should include an attack on the databank itself.
There are only two reported cases in which courts in Canada admitted mtDNA into evidence:
R. v. Woodcock and
R. v. Murrin.
In the mtDNA context, if a Caucasian haplotype has never before shown up in the FBI database (which occurs about half of the time), the probability of an unrelated individual sharing the same mtDNA profile is expressed as one in 556. This is expressed by means of a confidence interval of 95 per cent.
Recently, in an unreported decision in Newfoundland in
R. v. Turner, four apparently unrelated people in a small community had the same or similar mtDNA profiles.
In maritime, French-Canadian, and native communities, certain profiles may be quite common but they may not be in the database or may appear to be uncommon.
American courts have become comfortable with this evidence, but not all American lawyers have. For more details, see the article “Database Limitations on the Evidentiary Value of Forensic Mitochondrial DNA Evidence” by Frederika Kaestle, Rick Kittles, Andrea Roth, and Edward Ungvarsky in the American Criminal Law Review.
There is real debate about mtDNA science and its limits. As a result, it’s crucial not to ally ourselves too closely with the United States and its database. If this science is to have relevance in Canada, we need to develop our own random databases. What we don’t want is bad use of good science.
Rosalind Conway is a certified specialist in criminal litigation. She can be reached at [email protected].
