Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
Mitochondrial DNA (mtDNA) analysis has several forensic applications such as criminal investigations, identification of human remains, and missing person investigations. It is also the only type of DNA that is available from certain sample types such as hair shafts. The presence of mtDNA heteroplasmy within and between tissue types can lead to mtDNA sequence differences when comparing samples originating from the same individual. Studies on mtDNA heteroplasmy are increasingly being carried out for their implications in forensic interpretation of mtDNA sequences. Specifically, mtDNA in buccal swabs compared to hair samples from one individual may show differences in sequence due to heteroplasmy, and casework samples compared to reference swabs may exhibit differences that must be correctly interpreted to prevent faulty conclusions made by investigators and scientists alike. Establishing expected rates of heteroplasmy in mtDNA extracted from hair shaft samples and comparison to mtDNA extracted from buccal swab samples will lead to increased confidence in mtDNA interpretation.
The goals of this study were to (1) successfully sequence the entire mtDNA control region from buccal swab samples from 5 volunteers using Sanger sequencing, (2) amplify smaller (<300bp) sections of overlapping regions of the mtDNA control region from 15-20 hair shafts collected from three areas of the scalp using three methods of DNA extraction, and (3) evaluate mtDNA sequences from hair shafts and buccal swabs to identify heteroplasmy within and between samples. Overall, only 20% of the extracted hair samples resulted in half of Hypervariable Region 1 (HV1) being successfully sequenced from either the 5´ or 3´ end. Two out of five participants showed length heteroplasmy in the poly-cytosine region beginning at position 303 within the HV2 region. Point heteroplasmy was observed in one participant at one position in the buccal swab (nucleotide position 16093) as well as at two different positions in a hair sample (nucleotide positions 16258 and 16288) that did not show heteroplasmy in the buccal swab. The heteroplasmy seen in the buccal swab could not be compared to the hair sample as position 16093 did not fall within the successfully sequenced region in the hair. Although only a small subset of hair shafts were successfully sequenced, this study has succeeded in showing that mtDNA heteroplasmy seen in a hair shaft may not be present in buccal swab mtDNA. Further research into rates of heteroplasmy in hair shafts vs. buccal swabs is paramount to bettering the interpretative abilities of forensic scientists working with mtDNA and preventing false exclusions.
Bodnar, Sara R., "mtDNA Heteroplasmy in Hair Shafts versus Buccal Swabs for Forensic Applications" (2022). Graduate Theses, Dissertations, and Problem Reports. 11240.