[Sequence polymorphism of mitochondrial DNA and its forensic application]

We have investigated polymorphism of mitochondrial (mt) DNAs in the Japanese population. In order to compare 288-bp sequences (nucleotide positions 16,111 to 16,398) in the noncoding region, a 452-bp segment elongated by 82 bp at both sides of the target was amplified by PCR and analyzed directly by Taq cycle sequencing with FITC-labelled primers. A survey of 100 Japanese individuals revealed the existence of 66 types of mtDNAs. Among them, 10 types including two frequent types were shared by more than one individual. During this investigation, it was found that 19 types (from 25 individuals) possessed a common nucleotide replacement of T by C at position 16,189, by which a "C-continuous stretch" was formed, and that clear reading of their sequences was restricted in the region lying ahead of the C stretch on either forward or reverse sequencing. Cloning analysis of PCR product possessing the C stretch demonstrated that the length of the C stretch was heterogeneous. Consequently, we propose the following rules for mtDNA sequencing and its forensic application: 1) the replacement of T by C at position 16,189 is acceptable as a variation factor. 2) The number of Cs in the C stretch is tentatively fixed at 10.