No shortcut solution to the problem of Y-STR match probability calculation

Area of Science:

• Forensic Genetics
• Population Genetics
• Statistical Genetics

Background:

• Calculating match probabilities for Y-chromosomal short tandem repeats (Y-STRs) is more complex than for autosomal markers due to marker interdependence.
• The practical implications of this interdependence using real data have not been extensively studied, despite the high mutation rates of Y-STRs.

Purpose of the Study:

• To investigate the interdependence of Y-STR markers within the PowerPlex®Y23 (PPY23) set.
• To assess the practical relevance of marker interdependence on match probability calculations in forensic genetics.

Main Methods:

• Analysis of Y-STR haplotype data from 21 markers in the PPY23 set across six diverse populations.
• Conditional entropy assessment to evaluate statistical independence between markers and marker subsets.

Main Results:

• The PPY23 marker set cannot be decomposed into conditionally independent subsets.
• Over 94% of the joint entropy for 21 Y-STR markers is explained by the seven most rapidly mutating markers across all populations.
• Reduced marker sets still yield highly diverse partial haplotypes.

Conclusions:

• While a reduction in the number of Y-STR markers may be feasible for practical casework, match probability calculations remain challenging.
• Current methods for Y-STR haplotype frequency estimation require improvement to account for residual marker interdependence.