How convincing is a matching Y-chromosome profile?

Area of Science:

• Forensic Science
• Genetics
• Statistics

Background:

• DNA profiling, particularly Y-chromosome (Y-DNA) profiles, revolutionized forensic science but presents unique challenges in evaluating evidential weight.
• Existing methods struggle to account for relatedness in patrilineal clans and the impact of higher mutation rates in modern profiling kits.
• Defining relevant populations and deriving accurate population-based match probabilities for Y-DNA evidence is often infeasible.

Purpose of the Study:

• To develop a scientifically valid and comprehensible method for quantifying the evidential value of Y-chromosome DNA profiles.
• To address the challenges of relatedness and population definition in Y-DNA profile interpretation.
• To provide a robust approach for presenting Y-DNA evidence in legal settings.

Main Methods:

• Development of a simulation model to approximate the distribution of males with matching Y-profiles.
• Utilizing importance sampling reweighting to derive conditional distributions based on database frequencies.
• Testing the robustness of the distribution to variations in reproductive success and population growth rates.

Main Results:

• The proposed simulation model provides a robust approximation of the distribution of males with matching Y-profiles.
• The distribution's robustness was confirmed across different values for reproductive success variance and population growth rates.
• Conditional analysis on database frequency showed a modest impact on the distribution of matching males.

Conclusions:

• The developed simulation-based approach offers a conceptually simple and effective solution for evaluating Y-chromosome DNA evidence.
• This method allows for scientifically valid and easily understandable quantification of Y-profile evidence for judicial purposes.
• The approach enhances the reliable use of Y-DNA profiles in forensic casework, particularly in cases with mixed-source DNA.