Identification of contributors in the low-template and mixed samples by forensic mathematical estimation and experimental analysis

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Analyzing mixed or/and low-template DNA samples is challenging but inevitable in current forensic DNA test. We reevaluated autosomal STR multiplex typing kit and found that allele peak imbalance of heterozygote occurred even in a single person sample. Therefore, the determination of the heterozygous combination is not always reliable and the binary method which does not use the allelic peak heights still showed very powerful in mixed samples from 2 or 3 individuals.While it is often said that there is a risk that non-contributors cannot be excluded in a mixed sample, the simulated analysis using a large number of the mixed samples revealed that the first grade kin of the contributor is erroneously included as a contributor although its proportion is small. Moreover, 37 loci of autosomal STR were genotyped and the allele frequencies and the discriminating power were estimated in the Japanese population. Finally, the analytical procedure from mixed samples has been established.