Sizing short tandem repeat alleles in capillary array gel electrophoresis instruments

Area of Science:

• Forensic Science
• Genetics
• Molecular Biology

Background:

• The UK National DNA database utilizes the AMPF/STR SGM Plus multiplex system, comprising ten short tandem repeat (STR) loci and the Amelogenin locus.
• Accurate allele designation is critical for forensic DNA profiling and relies on comparison with standard allelic ladder markers.

Purpose of the Study:

• To assess and improve the accuracy of allele designation for STR loci analyzed using the Applied Biosystems 3700 instrument.
• To minimize the risk of allele misdesignation, particularly for high-molecular-weight alleles with higher standard deviations.

Main Methods:

• Analysis of AMPF/STR SGM Plus loci on a 96-capillary array gel electrophoresis instrument (Applied Biosystems 3700).
• Comparison of results with standard control allelic ladder markers.
• Implementation of guidelines for expert systems to minimize misdesignation risks.
• Computer simulation to test the efficacy and robustness of the procedures.

Main Results:

• High-molecular-weight alleles, such as HUMFIBRA, exhibited higher standard deviations (approx. 0.15), increasing the likelihood of misdesignation.
• Analyzing at least five different allelic ladders across the array helped estimate mean allele sizes and minimize designation errors.
• Developed guidelines for expert systems were effective in reducing misdesignation risks.

Conclusions:

• The implemented procedures, including multiple allelic ladder analyses and expert system guidelines, are robust for accurate STR allele designation in forensic applications.
• The methods ensure reliable DNA profiling essential for maintaining large forensic DNA databases.