mtDNA role in mixtures deconvolution

Mitochondrial DNA (mtDNA) usually has a negligible role in forensic casework and is only taken into account by forensic scientists if familiar testing is necessary or when genomic DNA (gDNA) is degraded. The forensic workflow normally does not include validated protocols to calculate the amount of mtDNA in a trace or the ratio between gDNA and mtDNA Because of the great inter-individual and tissue-specific variability of the number of mitochondria, the absence of this information may create misunderstandings in results interpretation. The aim of this work was to study mtDNA behaviour in mixtures composed of blood–saliva, blood–skin and saliva–skin; the GEP-ISFG group made similar analyses in the past, but only mixtures with semen were involved (representative of rape samples after differential lysis) and an almost complete absence of mtDNA was observed for the sperm fractions. In this project mixtures were prepared using two donor subjects with formerly known sequence information, having at least three different variants on the HV1 sequence, and DNA extraction was carry out on all samples. Autosomal STR markers were also analyzed in order to compare sequence results with gDNA electropherograms. Our experiment is the first time where skin tissue is included as a DNA source in mixtures where the role of mitochondria may be pivotal. These results could represent the first step of a more wide analysis involving real-time detection of mtDNA, in order to understand real gDNA/mtDNA ratios in different contexts.