BC 367 Experiment 5
Forensic Analysis of Canine DNA Samples
The advent of the Polymerase Chain Reaction (PCR) two decades ago revolutionized
forensic science. While older DNA typing techniques required a bloodstain the size of a dime,
PCR allows a DNA profile to be generated from a single fingerprint.
The most common method
of DNA analysis currently used by the forensic community is PCR at loci containing Short
Tandem Repeats (“PCR-STR”).
Short tandem repeats, also called microsatellites, arise when a
two-to-ten nucleotide sequence is repeated in the genome, much like a stutter. Following
isolation of DNA from a sample of interest, one or more hypervariable regions containing short
tandem repeats is amplified via PCR, leading to different fragment sizes across individuals.
Amplifying several hypervariable regions simultaneously in the same tube (“multiplexing”)
saves time, expense, and sample, as well as providing a highly discriminating test for identity.
In addition to nuclear DNA, cells also contain mitochondrial DNA (mtDNA). Both genomes
can be useful forensically, depending on the amount of sample, its quality, and the nature of the
MtDNA contains a hypervariable noncoding “control” region of about a thousand
Furthermore, amplification is possible from many different types of samples (e.g., hair shafts,
cheek cells, blood, teeth, and bone). Two other characteristics render mtDNA useful forensically:
it is present in high copy number (several hundred genomes per cell) and it is maternally
inherited (rendering individuals not only haploid, but also identical in sequence to their relatives
along the maternal line). MtDNA is most useful for identification of human remains when the
only reference material available is from relatives or when the remains are old and/or badly
damaged. For example, the remains of the Romanovs, the Russian Imperial family executed in
1918 by the Bolsheviks, were excavated in 1991 and subsequently positively identified via
grandmother was the mother of Czarina Alexandra.
More recently, mtDNA analysis confirmed
mountaineer Reinhold Messner’s version of his brother’s fatal climbing accident on Nanga
Parbat in 1970, disproving accusations that Reinhold had abandoned his brother in his own quest
for first-ascent glory.
Typically, mtDNA analysis is via sequencing of either the HV1 or HV2
subregion of the control region, both of which display an average 1-2% sequence variance in
Crime scene investigations often yield biological evidence from non-human sources such as