Evaluating Mixture Solution™- rapid and non-MCMC probabilistic mixture analysis

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• South Africa faces a high volume of property and sexual offense cases, leading to significant backlogs in forensic DNA analysis.
• Low-template DNA (LT-DNA) mixture casework presents challenges due to phenomena like allele dropout, complicating analysis with traditional methods.

Purpose of the Study:

• To compare the efficacy of DNAˑVIEW® Mixture Solution™ with the South African Police Service's (SAPS) current combined probability of inclusion (CPI) method.
• To evaluate the benefits of a continuous probabilistic model for analyzing forensic DNA mixtures, particularly in LT-DNA scenarios.

Main Methods:

• Analysis of sexual assault mixtures (casework and laboratory-prepared) with varying initial male DNA amounts (2-200 cells).
• Comparison of results obtained using DNAˑVIEW® Mixture Solution™ (continuous probabilistic model) versus the traditional CPI method (binary interpretation).

Main Results:

• The CPI method is largely ineffective for LT-DNA mixtures due to common dropout with contributions below 20-30 cells.
• DNAˑVIEW® Mixture Solution™ utilizes a continuous, probabilistic model that realistically incorporates dropout, increasing applicability to more cases (as few as 7 contributor cells).
• The continuous model provides stronger evidence for both inclusion and exclusion of suspects compared to CPI.

Conclusions:

• DNAˑVIEW® Mixture Solution™ offers a more robust and informative approach to forensic DNA mixture analysis than CPI, especially for LT-DNA.
• The probabilistic model enhances the power of evidence and expands the range of casework amenable to DNA mixture analysis.
• The method incidentally provides cell-number estimations, adding valuable perspective to mixture interpretation.