A forensic DNA profiling system for Northern European brown bears (Ursus arctos)

Area of Science:

• Forensic Genetics
• Wildlife Forensics
• Population Genetics

Background:

• Development of a DNA forensic profiling system for Northern European brown bear (Ursus arctos) is crucial for conservation and legal applications.
• Short tandem repeat (STR) markers are widely used in forensic science, but dinucleotide STRs present unique challenges compared to tetranucleotide loci.

Purpose of the Study:

• To validate a set of 13 dinucleotide STR loci as candidate markers for brown bear forensic DNA profiling.
• To assess the sensitivity, species specificity, and performance (precision, heterozygote balance, stutter ratios) of these dinucleotide STRs.
• To evaluate the genetic diversity and population structure within Northern European brown bear populations using the selected STRs.

Main Methods:

• Validation of 13 dinucleotide STR loci (G1A, G10B, G1D, G10L, MU05, MU09, MU10, MU15, MU23, MU26, MU50, MU51, MU59) for sensitivity and species specificity.
• Performance assessment including precision, heterozygote balance, and stutter ratios.
• Genotyping of 479 individuals from eight Northern European brown bear populations and analysis of genetic variation, Hardy-Weinberg equilibrium, linkage disequilibrium, population substructure (FST), and inbreeding (FIS).

Main Results:

• All STRs were successfully amplified with 0.6ng template DNA and showed no cross-species amplification issues.
• Dinucleotide STRs exhibited more pronounced stutter ratios and heterozygote imbalance compared to human forensic tetranucleotide loci, indicating potential difficulties in interpreting mixed DNA profiles.
• Locus MU26 was excluded due to null alleles. The remaining 12 STRs showed low probabilities of identity (<1.1×10⁻⁹) and sibling identity (<1.3×10⁻⁴), suggesting suitability for individual identification in single-source samples.
• Significant genetic differentiation was detected among some populations (average FST = 0.09).

Conclusions:

• The 12 validated dinucleotide STR loci are suitable for individual brown bear identification in single-source forensic samples.
• Challenges related to stutter and heterozygote balance in dinucleotide STRs necessitate careful interpretation, especially in complex samples.
• The developed STR panel provides robust genetic information for brown bear population studies and forensic applications in Northern Europe.