[Sequence polymorphism of mitochondrial DNA and its forensic application]

Area of Science:

• Genetics
• Forensic Science

Background:

• Mitochondrial DNA (mtDNA) exhibits polymorphism, crucial for population genetics and forensic applications.
• Direct sequencing of mtDNA noncoding regions can be challenging due to sequence variations.

Purpose of the Study:

• To investigate mitochondrial DNA polymorphism in the Japanese population.
• To analyze sequence variations, particularly a T-to-C replacement at position 16,189, and its impact on sequencing.
• To propose updated guidelines for mtDNA sequencing in forensic contexts.

Main Methods:

• PCR amplification of a 452-bp segment of the mtDNA noncoding region (nt 16,111-16,398).
• Direct Taq cycle sequencing using FITC-labelled primers.
• Cloning analysis to characterize the 'C-continuous stretch' variation.

Main Results:

• A survey of 100 Japanese individuals identified 66 distinct mtDNA types.
• Ten mtDNA types were shared among individuals, with two being particularly frequent.
• Nineteen types (from 25 individuals) showed a T-to-C replacement at position 16,189, forming a 'C-continuous stretch' that hindered sequence readability.
• Cloning revealed heterogeneous lengths of the 'C-continuous stretch'.

Conclusions:

• The T-to-C replacement at position 16,189 should be recognized as a valid variation factor in mtDNA analysis.
• A standardized length of 10 Cs for the 'C-continuous stretch' is proposed for consistent forensic application.
• These findings necessitate revised protocols for accurate mtDNA sequencing and interpretation in forensic investigations.