Abstract
Objective To confirm the tri-allelic of STR loci in parentage test and then identify the biological parents by likelihood calculation. Methods Chelex-100 method was used to extract blood genomic DNA of 7665 individuals, and genetic profiles of 20-30 STR loci were detected by multiplex fluorescence PCR and capillary electrophoresis. Results Tri-allelic patterns were observed at Penta D, D21S2055 STR loci in one person, the detectable frequency was 0.13‰(1/7665). Two cases showed fluorescence intensity, peak height, and peak area of 1∶2 in D21S11 locus, and the detection frequency was 0.26‰(2/7665). The combined parentage index (CPI) value was 2.4789×1020. Conclusion When tri-allelic pattern was observed in parentage test one should exclude the influence of reagent and contamination firstly, then add STR loci of the same chromosome and analyze genetic information of parents, and calculate the CPI to identify the biological blood relationship. Key words: Tri-allelic; STR; Parentage test; Combined parentage index
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