Interpreting Y chromosome STR haplotype mixture.

Area of Science:

• Forensic Genetics
• Population Genetics
• Molecular Biology

Background:

• Y-short tandem repeat (STR) haplotype mixture interpretation presents unique challenges in forensic DNA analysis due to the lack of recombination.
• These challenges differ from autosomal DNA markers, requiring specialized interpretation methods.

Purpose of the Study:

• To describe and evaluate methods for calculating the probability of exclusion (PE) and likelihood ratio (LR) for Y-STR mixture interpretation.
• To incorporate population substructure into these calculations for enhanced accuracy.

Main Methods:

• Developing approaches for PE and LR calculations that account for population substructure.
• Generating candidate lists of possible contributor haplotypes from a reference database.
• Simulating Y-STR mixtures using two or three haplotypes from the US forensic Y-STR database.

Main Results:

• The probability of exclusion (PE) is influenced by database size, with an average PE of at least 0.995 for two-person mixtures using a 500-haplotype database.
• PE decreases as the number of contributors increases.
• For two-person mixtures, the average number of candidate haplotypes is low (3.73), with 95% having ≤10 candidate haplotypes, indicating high interpretability.

Conclusions:

• The described PE and LR methods, incorporating population substructure, offer robust approaches for Y-STR mixture interpretation.
• These methods demonstrate high discriminatory power, particularly for two-person mixtures, with a significant percentage uniquely explained by their composition.
• The study provides valuable tools for forensic scientists dealing with complex Y-STR evidence.