Impact of population size on population genetic analysis of Short Tandem Repeat (STR) allelic data, forensic and paternity parameters and its effect on forensic DNA analysis.

The selection of an appropriate STR allelic frequency database is the prerequisite for assessing the evidentiary value of DNA evidence. Four data sets comprising 50, 100, 200, and 500 samples were evaluated in 21 autosomal STR markers in the Indian and the Bahrain population. Allelic richness showed an increasing trend with the increase in sample size i.e., 193 and 201 (50 samples), 217 and 221 (100 samples), 255 and 238 (200 samples), and 292 and 285 (500 samples) in both the populations. TPOX and D13S317 markers did not show any increase in allele number, whereas SE33 markers showed the highest increase in both populations. With the increase in sample size, 70 (Bahrain population) and 100 (Indian population) alleles having < MAF were detected. Similarly, 37 and 47 previously undetected alleles could be detected when the sample size was increased from 50 to 500 in the Indian and Bahrain populations respectively. In the Indian population, Match probability, decreased with a 500-sample size, whereas, the PIC, PE, Heterozygosity, and PI increased with the increase in sample size. Further, database size did not show any statistical difference in the outcome of the Paternity Index value in the 50 paternity trio cases studied.