A novel fluorescent quadruplex STR typing system and the allele frequency distributions in a Thai population

We have previously reported a new triplex amplification and typing system by silver staining for three short tandem repeat (STR) loci, 9q2h2 (D2S3020), D15S233, and D14S299 without "microvariant" alleles such as .1, .2, and, .3 alleles in the Japanese population. In the present study, we established a new quadruplex system with an additional locus D7S809 using primer sets labeled with fluorescent multi-color dyes. Using this system, we genotyped 183 Thai people, found only one "microvariant" allele (allele 20.2) at D7S809, and calculated allele frequencies and some statistical properties at these four STR loci. From these allele frequencies at four STR loci, we performed three statistical analyses including a homozygosity test, a likelihood ratio test, and an exact test for Hardy-Weinberg equilibrium (HWE). Deviations from HWE (p < 0.05) were observed only in the two tests at the locus D7S809. In the present study, we compared the allele frequencies at these four loci in the Thai population to those in the Japanese population described previously. Consequently, all observed heterozygosities and power of discrimination (PD) at those loci in the Thai population were higher than 0.8 and 0.9, respectively, and all statistical values for discriminating power in the Thai population were slightly higher than those in the Japanese population. The combined paternity exclusion rate (combined PE) in the Thai population (0.978) was almost the same as that in the Japanese population (0.971). Therefore, this novel PCR amplification and typing system for four STR loci would be a convenient and informative DNA profiling system in the forensic field.