Practical applications of genotypic surveys for forensic STR testing.

Area of Science:

• Forensic genetics
• Population genetics
• Molecular biology

Background:

• Accurate genotype frequency estimation is crucial for forensic DNA analysis.
• Population surveys are essential for establishing allele frequencies for DNA profile databases.
• Multiallelic loci require robust methods for reliable frequency estimation.

Purpose of the Study:

• To assess the reliability of genotype frequency estimation for 13 worldwide forensic short tandem repeat (STR) loci in two distinct ethnic populations.
• To evaluate the impact of deviations from Hardy-Weinberg proportions and linkage equilibrium on forensic calculations.
• To provide allele frequency estimates for African American and U.S. Caucasian populations for use in forensic casework.

Main Methods:

• Genotyping of 195 African Americans and 200 U.S. Caucasians at 13 STR loci using sex-specific AmpFlSTR multiplexes.
• Statistical analysis including homozygosity tests, log likelihood ratio tests, exact tests, and Karlin interclass correlation tests.
• Assessment of Hardy-Weinberg proportions and linkage disequilibrium for all 13 STR loci.

Main Results:

• Heterozygosity at STR loci ranged from 0.57 to 0.89, with 7 to 21 alleles per locus.
• Deviations from Hardy-Weinberg proportions and linkage equilibrium were not significant enough to impact genotype frequency estimation.
• The calculated probability of a coincidental match for a 13-locus DNA profile was extremely low (1 in 1.8x10^15 for African Americans, 1 in 3.8x10^14 for U.S. Caucasians).

Conclusions:

• The Hardy-Weinberg equation and population-specific allele frequency estimates provide reliable multilocus DNA profile frequency estimates for forensic casework.
• The established allele frequencies and statistical methods support the discriminatory power of the 13 STR loci in forensic investigations.
• The study confirms the robustness of STR analysis for individual identification in diverse populations.