Resolving kinship degrees with identity-by-descent coefficients: Limits and insights from a simulation study

Area of Science:

• Forensic genetics
• Population genetics
• Statistical genetics

Background:

• Kinship analysis in forensic genetics demands precise relatedness degree determination.
• Identity-by-descent (IBD) coefficients are standard but their discriminatory power in likelihood ratio (LR) frameworks for distant relatives is unclear.

Purpose of the Study:

• To develop and evaluate a maximum LR approach with dynamic thresholds for IBD-based kinship discrimination.
• To assess the system's performance in distinguishing various relationship degrees using different genetic marker panels.

Main Methods:

• Developed a maximum LR approach utilizing LRkin calculations.
• Tested competing hypotheses (H0: relationship i vs. H1: relationship j, i≠j).
• Assessed performance across virtual panels including STR (21-500 loci) and SNP (6445-16,109 loci) datasets.

Main Results:

• The LRkin-based maximum LR method successfully differentiated closer relationships (parent-offspring, full-sibling, second-degree).
• The method showed limitations in distinguishing more distant relationships, even with extensive genetic markers.
• Increased genetic markers enhance inference accuracy but IBD-based LR has limitations.

Conclusions:

• Calculating LRkin aids in reducing relationship inference errors, though it doesn't improve inference accuracy.
• The LR approach is effective for close relatives but requires further development for distant kinship identification.
• More genetic markers improve accuracy, but inherent limitations exist in distinguishing distant relationships using IBD-based LR.