| Objective(s): Short tandem repeat(STR)typing has been widely used in forensic cases,and STR locus length polymorphism typing based on capillary electrophoresis platform has become the gold standard for individual identification.This study is based on the next generation sequencing technology to amplify and sequence DNA samples from representative populations across the country.Based on the sequence polymorphism,the allele typing of 122 STR loci is statistically studied,and the differences between different populations are evaluated,with a view to improving and updating the NGS typing data of 122 loci,providing basic data for the construction of population genetics and STR databases and reference standards that can be applied to forensic case detection.Methods:A total of 559 unrelated individual DNA samples from the Han population in Beijing,Changshu and Dalian were collected in this study.The sample DNA was extracted using M48 magnetic bead extraction and purification kit,and the library was prepared using STRSeq Typer122 second-generation sequencing STR typing kit through compound amplification.The Mi Seq FGx sequencing platform was used for sequencing,and the Forensic Typer forensic genetic marker second-generation sequencing data analysis software was used for sample typing analysis.The data output by the sequencer is transformed into intuitive genetic information through bioinformatics.Based on sequence polymorphism and length polymorphism,the allele typing and frequency of 122 STR loci were statistically compared,and the forensic genetic parameters were calculated to evaluate the differences between different populations.Results:This study conducted data analysis on 459 population samples after screening according to the data quality control conditions.The complete and reliable allele typing and allele frequency of 122 STR loci based on sequence polymorphism and length polymorphism have been obtained through the second-generation sequencing platform.The difference of the three populations in Beijing,Changshu and Dalian was evaluated,and the Fst values based on length polymorphism and sequence polymorphism were less than 0.05,indicating that the genotypic differentiation of the three Han populations was not obvious.The long polymorphism typing is basically consistent with the CE typing results.By comparing the results of sequence polymorphism and length polymorphism typing,a total of 1,080 alleles were observed in three Han populations based on length polymorphism,with frequencies ranging from 0.0011 to 0.9636,and expected heterozygosity(He)of 63 autosomal STR loci ranging from 0.5985(D2S1360)to 0.9114(Penta E);The individual identification probability(PD)is between 0.7854 and 0.9824,and the cumulative individual identification probability(CPD)is greater than 0.9n [n=69](the value is about 69 9 after the decimal point);The non-parent exclusion probability(PE)is between 0.2601 and 0.7639,and the cumulative non-parent exclusion probability(CPE)is 1-2.13×10-21,greater than 0.999 999 999 999 999 999.A total of 1,934 alleles were observed based on sequence polymorphism,with frequencies ranging from 0.0011 to 0.9636,and expected heterozygosity(He)ranging from 0.6084(D1S1627)to 0.9454(D7S1517);The individual identification probability(PD)is between 0.7854 and 0.9882,and the cumulative individual identification probability(CPD)is greater than 0.9n [n=76](the value is about 76 9 after the decimal point).The non-parent exclusion probability(PE)is between 0.2888 and 0.8217,and the cumulative non-parent exclusion probability(CPE)is 1-2.21×10-24,greater than 0.999999 999 999 999 999 999.There were 43 autosomal STR loci that were homozygous based on length polymorphisms and heterozygous based on sequence polymorphisms, and a total of 696 isometric heterozygotes were found in each locus,and the proportion of isometric heterozygotes in length homozygotes was about 16%,accounting for about 4% of the total sample number.The average exclusion rate of cumulative triad based on length polymorphism of 16 X chromosome STR loci is0.999 999 973 755 909,the average exclusion rate of cumulative triad is 0.999 993104 105 413,and the cumulative individual identification probability(CPDf)in female individuals is 0.999 999 999 999 999 612 2;The cumulative individual recognition probability(CPDm)of male individuals is 0.999 999 996 427 505;The average exclusion rate of cumulative triad based on sequence polymorphism is 0.999999 995 019 575,the average exclusion rate of cumulative triad is 0.999 998 229 119416,and the cumulative individual identification probability(CPDf)among female individuals is 0.999 999 999 999 999 700 6;The cumulative individual recognition probability(CPDm)among male individuals is 0.999 999 998 623 135.The haplotype difference(HD)and resolution(DC)of 42 Y-STR loci were 0.9999 and 0.9872,respectively.A total of 328 haplotypes were detected in 331 males,of which 325 were detected once and the other three were detected twice.Conclusion(s):The sequence polymorphism typing data of 122 STR loci obtained based on the second generation sequencing platform in this study are authentic and reliable.The alleles based on core repeat region and flank sequence variations are updated and supplemented,resulting in more refined allele typing compared to length polymorphism performance.The cumulative forensic genetic parameters meet the identification criteria for individual identification and paternity testing,and the cumulative matching probability is 30,000,000 times lower than length polymorphism,All the data obtained in the study provide basic data for reference standards that can be applied to forensic case detection. |
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