In the routine of autosomal STR genotyping for forensic aims, tri-allelic patterns could be occasionally observed at a single locus in phenotypically normal individuals. Two predominant types of tri-allelic variants have been nominated. Uneven intensities of three alleles are normally considered as the Type 1 pattern, and balanced height of three alleles are considered as the Type 2 pattern. In this study, the prevalence of tri-allelic patterns at the CODIS STR loci was investigated in global populations based on previous reports. The frequencies of the Type 1 and Type 2 pattern manifest a correlation with the germline mutation rates at the CODIS STR loci. The irregular high frequencies of the Type 2 pattern at TPOX with low germline mutation rates could attribute to the stable inheritance of genomic rearrangement from ancestral origin. Furthermore, results from genetic pattern analysis show that only a single allele from STRs with the Type 1 pattern could be transmitted from parents to offsprings, while a single allele and a combination of two alleles from STRs with the Type 2 pattern present an equal opportunity of transmission from parents to offsprings. Altogether, these results provide a genetic portrait of STRs with tri-allelic patterns, which will help the genetic interpretation of tri-allelic patterns in forensic practice.

在以法医为目的的常染色体STR基因分型中，表型正常的个体偶尔会在单个基因座观察到三等位基因模式。已经提名了两种主要类型的三等位基因变体。通常将三个等位基因的强度不均视为1型模式，将三个等位基因的平衡高度视为2型模式。在这项研究中，根据以前的报道，在全球人群中调查了CODIS STR位点的三等位基因模式的患病率。1型和2型模式的频率表明与CODIS STR位点的种系突变率相关。具有低种系突变率的TPOX处2型模式的不规则高频可能归因于祖先基因组重排的稳定遗传。此外，遗传模式分析的结果表明，只有具有1型模式的STRs的单个等位基因可以从亲本传播给后代，而具有2型模式的STRs的单个等位基因和两个等位基因的组合具有相同的机会从父母传给后代。总之，这些结果提供了具有三等位基因模式的STR的遗传肖像，这将有助于法医实践中三等位基因模式的遗传解释。