Abstract: Objective To evaluate the diversity of combined paternity index (CPI) of multiple STR lociwhen different population allele frequencies was used to calculate the paternity index. Methods CPI of 13CODIS (combined DNA index system) loci for 108 trio cases and 108 duo cases selected randomly werecalculated by using five Chinese Han population allele frequencies, respectively. Results The CPI rangefor trio cases and duo cases were 2077.63- 50897711626.46 and 25.12- 2998685141, respectively. Whendifferent population allele frequencies were applied to the same case, the ratio of maximum CPI and min-imum CPI, which was more than 100, for trio cases and duo cases were 20 cases(19.52%) and 13 cases(12.04%) , respectively. Conclusion The variation of CPI value of the CODIS loci was obvious with dif-ferent allele frequencies. To prevent the error causing by uncertain allele frequencies, a conservative CPIvalue should be calculated in paternity testing.

Key words: paternity testing, paternity index, allele frequencies, short tandem repeats, CODIS