Practical applications of genotypic surveys for forensic STR testing

Legitimate genotype frequency estimation for multiallelic loci relies on co mponent allele frequencies, as population surveys represent only a fraction of possible DNA profiles. Multilocus genotypes from two ethnic human popul ations, African American (n=195) and U.S. Caucasian (n=200), were compiled at 13 STR loci that are used worldwide in forensic investigation (D3S1358, vWA, FGA, D16S539, TH01, TPOX, CSF1PO, D8S1179, D21S11, D18S51, D5S818, D13 S317, and D7S820). Sex-specific AmpFISTR(TM) multiplexes provided stringent PCR-based STR typing specifically optimized for multicolor fluorescence de tection, Heterozygosity at each STR locus ranged from 0.57 to 0.89 and enco mpassed from seven (TH01) to twenty-one (D21S11) alleles. Homozygosity test s, tests based on the distinct numbers of observed homozygous and heterozyg ous classes, log likelihood ratio tests, and exact tests assessed that the degree of divergence from theoretical Hardy-Weinberg proportions for all 13 STRs does not have practical consequence in genotype frequency estimation. Departures from linkage equilibrium, between loci, that imposed significan ce to forensic calculations were not indicated by observed variance of the number of heterozygous loci or Karlin interclass correlation rests. For for ensic casework, reliable multilocus profile estimates may be obtained from the product of component genotype frequencies, each calculated through appl ication of the Hardy-Weinberg equation to population database allele freque ncy estimates reported here. The average probability that two randomly sele cted, unrelated individuals possess an identical thirteen-locus DNA profile was one in 1.8X10(15) African Americans and one in 3.8X10(14) U.S. Caucasi ans. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.