Combined effects of multiple linked loci on pairwise sibling tests

Area of Science:

• Forensic Science
• Genetics
• Population Genetics

Background:

• Advanced multiplex STR systems, such as PowerPlex Fusion, feature multiple linked locus pairs.
• Conventional systems like Identifiler have fewer linked loci.
• Linkage between loci can potentially impact the accuracy of sibling relationship testing.

Purpose of the Study:

• To simulate and evaluate the effects of linked locus pairs on sibling tests.
• To compare the impact of linkage in advanced (PowerPlex Fusion) versus conventional (Identifiler) STR systems.
• To assess whether ignoring linkage affects classification in sibling tests.

Main Methods:

• Simulation of 100,000 pairs of full siblings and nonrelatives using Japanese population allele frequencies.
• Calculation of likelihood ratios, both accounting for and ignoring locus linkage.
• Evaluation of single and combined linkage effects, and their impact on test classification.

Main Results:

• Ignoring linkage in Identifiler analysis resulted in effect multipliers of 0.645-1.746.
• Ignoring linkage in PowerPlex Fusion analysis yielded effect multipliers of 0.217-7.390.
• False conclusive or inconclusive results were rare even with PowerPlex Fusion when linkage was ignored.

Conclusions:

• Advanced STR systems significantly enhance sibling test performance.
• The benefits of increased loci in advanced systems outweigh the potential adverse effects of linkage.
• PowerPlex Fusion improves sibling testing, with additional loci offering substantial advantages over linkage concerns.