Figure 8.2 Diagram of the human mtDNA control region. Positions of the primers are indicated by arrows. For analysis of aged samples, two sets of PCR primers are used to amplify overlapping fragments -250 bp long: L15997/H16236 and L16159/ H16401 for HV-I and L29/H285 and L172/H408 for HV-II
If the sequences are unequivocally different, then the samples can be excluded as having originated from the same source. If the sequences are the same, then the reference and evidence samples cannot be excluded as potentially being from the same source. In cases where the same heteroplasmy is observed in both the known and unknown samples, its presence may increase the strength of the evidence. If heteroplasmy is observed in the questioned sample but not in the known sample, a common maternal lineage cannot be excluded. If the two samples differ by a single nucleotide, and there is no indication of heteroplasmy, the interpretation may be that the results are inconclusive. However, a one-nucleotide difference between two samples, on occasions, may provide evidence against the samples either originating from the same source or having the same maternal lineage; in particular, where both samples are a tissue such as blood, a single nucleotide difference points towards exclusion of a common maternal origin. The source of the tissue being investigated should be taken into consideration, because differences in mtDNA sequences due to mutations seem to be more likely between e.g. hair and blood than between two blood samples taken from the same individual.
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