Joint match probabilities for Y chromosomal and autosomal markers

Area of Science:

• Forensic Genetics
• Population Genetics
• Statistical Genetics

Background:

• Determining joint match probabilities for Y chromosome and autosomal DNA markers is crucial in forensic science.
• Understanding the statistical independence of Y chromosome and autosomal markers is key for accurate identification.

Purpose of the Study:

• To empirically test the association between Y chromosome and autosomal markers.
• To recommend a theoretical framework for calculating joint match probabilities.
• To evaluate the impact of population substructure on these calculations.

Main Methods:

• Statistical analyses of association between autosomal genotypes (13 loci) and Y chromosome haplotypes (10 loci).
• Data collected from 16 US populations representing diverse ancestries (European, African, Hispanic, Native, Asian-American).
• Evaluation of marker independence and development of a joint match probability calculation method.

Main Results:

• Empirical tests suggest independence between Y chromosome and autosomal markers, though minor dependencies may exist.
• A method for computing joint match probabilities by multiplying Y haplotype frequency with corrected autosomal frequency is recommended.
• Adjustments for population substructure (theta correction) are necessary and shown to have a small, often trivial, impact when conditioning on Y chromosome matches.

Conclusions:

• The multiplication of Y haplotype frequency and corrected autosomal frequency is an appropriate method for calculating joint match probabilities.
• The statistical independence of Y chromosome and autosomal markers simplifies joint probability calculations in most forensic contexts.
• While population substructure requires correction, its additional impact when conditioning on Y chromosome markers is minimal.