Detection and analysis of three alleles in forensic DNA identification
Objective Exploring the types and characteristics of three alleles providing scientific basis for forensic appraisers to accurately analyze and determine the phenomenon of three alleles in judicial practice.Methods Collect 6 case samples from the Forensic Medicine Judicial Identification Center of Xi'an Jiaotong University,DNA was extracted using Chelex-100,and STR genotyping was analyzed by multiplex PCR amplification and capillary electrophoresis.Results The showed that 5 out of 39 STR alleles were detected with three alleles,including D18S51(3 cases),D21S11(2 cases),and D2S441(1 cases),D2S1338(1 cases),and D21S1270(1 cases).The results were consistent using different reagent kits,and the peak height area of the type 1 phenotype was uneven,with a detection rate of 50％(4/8);type 2 exhibits a balanced peak height and area,with a detection rate of 50％(4/8).Sequencing confirmed that D2S441 is the simple sequence STR locus at 2pl4,repeat unit TCTA,and D2S1338 is the complex sequence STR locus at 2q35,repeat units TGCC and TTCC.Conclusion When encountering three alleles in DNA identification,different reagent kits need to be used for verification,or the addition of alleles in sex chromosomes,parental index should be calculated carefully.
Short tandem reportThree-banded alleleDNA identification
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