Empirical Classification of Tri-Allelic Genotype Cases and Parentage Index Calculation

doi:10.12116/j.issn.1004-5619.2025.550604

Abstract

Abstract:

Objective To standardize the calculation method of the parentage index （PI） for short tandem repeat （STR） tri-allelic genotypes, thereby ensuring the accuracy and reliability of parentage tes‑ ting conclusions. Methods A systematic analysis of 160 real cases was conducted. A classification system was constructed based on the occurrence mechanisms and inheritance patterns of STR tri-alleles, and the PI calculation method was optimized by integrating previous research findings with empirical data. Results A mechanism-based classification system for STR tri-allelic genotypes was established, comprising Type I （2 subtypes）, Type II （6 subtypes）, and the trisomic type （2 subtypes）. On this basis, a standardized PI calculation method covering all categories of STR tri-allelic genotypes was developed. Conclusion This study provides methodological guidance for the scientific and standardized calculation of PI for STR tri-allelic genotypes and offers an important reference for the formulation and refinement of relevant industry standards.

Key words: forensic genetics, STR, tri-allelic pattern, trisomy, parentage index

CLC Number:

Le YANG, He REN, Yan SHI, Chong CHEN, Li JIA, Qian YANG, Yacheng LIU, Jiangwei YAN. Empirical Classification of Tri-Allelic Genotype Cases and Parentage Index Calculation[J]. Journal of Forensic Medicine, 2026, 42(3): 254-260.

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URL: http://www.fyxzz.cn/EN/10.12116/j.issn.1004-5619.2025.550604

http://www.fyxzz.cn/EN/Y2026/V42/I3/254

References 9

[1]	CLAYTON T M， GUEST J L， URQUHART A J， et al. A genetic basis for anomalous band patterns encountered during DNA STR profiling[J]. J Forensic Sci，2004，49（6）：1207-1214.
[2]	PICANÇO J B， RAIMANN P E， MOTTA C H A S DA， et al. Identification of the third/extra allele for forensic application in cases with TPOX tri-allelic pattern[J]. Forensic Sci Int Genet，2015，16：88-93. doi：10.1016/j.fsigen.2014.11.016 .
[3]	BRINKMANN B， KLINTSCHAR M， NEUHUBER F， et al. Mutation rate in human microsatellites： Influence of the structure and length of the tandem repeat[J]. Am J Hum Genet，1998，62（6）：1408-1415. doi：10.1086/301869 .
[4]	马晓燕，孙宏钰，黎青. 常染色体STR三等位基因型在法医DNA分析中的研究进展[J].法医学杂志，2023，39（3）：240-246. doi：10.12116/j.issn.1004-5619.2023.530210 .
	MA X Y， SUN H Y， LI Q. Research progresses of tri-allelic patterns in autosomal STR in forensic DNA analysis[J]. Fayixue Zazhi，2023，39（3）：240-246.
[5]	YANG Q R， YAO Y N， SHAO C C， et al. Calculation of the Paternity Index for STR with tri-allelic patterns in paternity testing[J]. Forensic Sci Int，2021，324：110832. doi：10.1016/j.forsciint.2021.110832 .
[6]	上海市司法鉴定协会. 常染色体STR三等位基因型的亲权指数计算技术规范：T/ [S].上海，2025.
	Shanghai Association of Forensic Science. Technical specification for the calculation and application of parentage index for autosomal STRs with tri-allelic patterns： T/ [S]. Shanghai，2025.
[7]	林汉光，许传超，唐剑频，等. 常染色体STR三体基因座父权指数计算方法探讨[J].中国法医学杂志，2013，28（5）：400-403. doi：10.13618/j.issn.1001-5728.2013.05.035 .
	LIN H G， XU C C， TANG J P， et al. The calculation methods of paternity index for abnormal autosomal STR loci of trisomysyndrome[J]. Zhongguo Fayixue Zazhi，2013，28（5）：400-403.
[8]	KATJU V， BERGTHORSSON U. Copy-number changes in evolution： Rates， fitness effects and adaptive significance[J]. Front Genet，2013，4：273. doi：10.3389/fgene.2013.00273 .
[9]	YANG Q R， SHEN Y W， SHAO C C， et al. Genetic analysis of tri-allelic patterns at the CODIS STR loci[J]. Mol Genet Genomics，2020，295（5）：1263-1268. doi：10.1007/s00438-020-01701-w .

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