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P145 – MtDNA Analysis from Hair Samples: Removal of Exogenous DNA and Interpretation of Results

16:19

Wednesday August 19^th

Station 15

Duration: 12 minutes

04. Forensic biology

Frédéric Grosjean

Mitochondrial DNA (mtDNA) analysis is frequently used in forensic genetics when nuclear DNA is limited, such as in degraded items or rootless hairs. A key challenge lies in distinguishing endogenous mtDNA from exogenous DNA originating from biological material adhering to the sample. This is particularly critical when hairs recovered from a scene are recovered in what appears to be the victim’s blood.

This study evaluates a two-step DNA extraction protocol designed to separate exogenous (first lysis) from endogenous (second lysis) mtDNA. A total of 48 hair fragments (~1 cm), with and without roots, were analyzed. In the first experiment, the two-step protocol was compared to a conventional single-step extraction. While all hairs with roots yielded interpretable mtDNA profiles regardless of method, reduced success was observed for rootless hairs with the two-step protocol, likely due to DNA loss during the initial lysis.

In a second experiment, hairs artificially contaminated with blood were processed using the two-step protocol. Endogenous mtDNA profiles were successfully produced after the second lysis, with no detectable contribution from the exogenous known blood donor. However, some rootless hairs yielded no usable profiles.

These results demonstrate that the two-step protocol can effectively separate endogenous from exogenous mtDNA, although efficiency is reduced in low-template items. The approach was successfully applied in casework and the results evaluated using a probabilistic approach.

Authors

Frédéric Grosjean (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Switzerland)
Tacha Hicks (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Switzerland)
Vincent Castella (Unit of Forensic Genetics, University Center of Legal Medicine, Lausanne - Geneva, Switzerland)

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P145 – MtDNA Analysis from Hair Samples: Removal of Exogenous DNA and Interpretation of Results

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