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The objective of this case is to use forensic nuclear and mitochondrial DNA, mtDNA, analysis to determine the identity of Professor Millstone’s killer. Suspects include Professor Hedd and a disgruntled student. Canine hair and saliva were taken from the crime scene, from Professor Hedd’s female dog, the student’s male dog, and known control male and female dogs. DNA was extracted from hair and saliva using Tissue and Hair Extraction Kits and DNA IQ Kit from Promega. Specific loci of the nuclear DNA, PEZ 2, PEZ 15 and VWF.X, were amplified using the Polymerase Chain Reaction, or PCR. In addition, loci from mitrochondrial DNA and sex chromosomes were amplified using specific canine primers. These amplified DNA sequences were run on either 6% polyacrylamide gels, PAGE gels, or 1.5% agarose gel, which were stained and examined with SYBR Gold stain for PAGE gels or ethidium bromide for agarose. The resultant bands were compared to the exACT Gene 50 bp gene DNA ladder from Fisher Scientific. After measuring significant bands, plots of the logs of estimated base pairs were generated.
After observing PEZ2 bands, it was determined that they provided insufficient data to aid in our analysis. Mitochondrial DNA samples obtained from the victim and two suspects indicated that all dogs are all of the same maternal line. This is in keeping with the fact that both suspects’ dogs came from the same breeder. The VWF.X samples provide similar number of base pairs among all dogs, which increases probability that the dogs of the suspects are immediately related. The PEZ 15 samples, though not fully complete in hair and saliva, reinforce the conclusion from the VWF.X samples that the dogs of the suspects share the same maternal lineage and paternal lineage. Gender analysis of the samples provides inconclusive and inconsistent data compared to the known genders of the suspects’ dogs.
Findings from mtDNA analysis do support a constant profile independent of tissue type. There is a probability of 5.1E-3 for two mtDNA fragments from random canines to match in the way the mtDNA fragments matched in samples between suspects and the crime scene. mtDNA analysis does not exclude any of the suspects from further investigation. For the VWF.X nuclear locus, the probability that two unrelated canines would share the same number of short tandem repeats as both suspects and evidence do, is 0.319. For the PEZ 15 nuclear locus, the probability that two unrelated canines would share the same number of short tandem repeats as both suspects and evidence do, is 0.043. The probability that two that two unrelated canines would share the same bands in mtDNA and nuclear DNA analysis as both suspects and evidence do, is 6.99E-5. This final calculated probability certainly implicates the two suspects, but it does not conclusively determine the identity of the killer.
Evidence not only does not single out a suspect but also raises questions which further investigation must address. One issue that arises is that the two suspects’ dogs are clearly closely related, so there must be additional background checks on the two canines and the breeder of the dogs. In addition, other dogs bred from the same two parental lines must be investigated to ensure no other suspects in this case.
Inconsistent results from all canine samples, specifically from the gender analysis, suggest that samples from the crime scene and from suspects’ dogs must be recollected. Because of the nature of the genetic similarities of the suspects’ dogs, gender analysis will provide the most conclusive evidence towards one suspect’s dog over the other.
Potential sources of error include contamination of the collected samples, experimental error in mixing of PCR reagent and amplification, and damage to PAGE gel.