Abstract：
Short tandem repeat (STR) is regarded as a crucial tool for personal identification as well as parentage testing. Thus, genotyping errors of STRs could have negative effects on the reliability of forensic identification. A null allele at the combined DNA index system (CODIS) core loci D2S1338 was found in a father-daughter pair with the AGCU Expressmarker 22 kit which was a commonly used commercial kit during our daily laboratory work. This null allele caused the father and daughter to not conform to the laws of inheritance, thus potentially generating erroneous conclusions that excluded parentage. To figure out the reason for this phenomenon, re-amplification with new primers and then large fragment Sanger sequencing was conducted. We found a G to G/T variation at the position which is fifty-nine bases away from the 3\' end of the core repeat in both samples. This probably could be considered a novel variant at the primer binding region which had not been reported that resulted in the emergence of the null allele. We also found that there was more than one single-nucleotide polymorphism (SNP) with minor allele frequency (MAF) greater than 0.1 in the upstream and downstream sequences of D2S1338. When designing primers for amplification of D2S1338, the possible adverse results of these SNPs should be taken into account and avoided.
摘要：
短串联重复（STR）被认为是个人识别和亲子关系测试的重要工具。因此，STR的基因分型错误可能会对法医鉴定的可靠性产生负面影响。在父女对中发现了组合DNA索引系统（CODIS）核心基因座D2S1338的无效等位基因，AGCUExpressmarker22试剂盒是我们日常实验室工作中常用的商业试剂盒。这个无效等位基因导致父亲和女儿不符合遗传规律，因此可能会产生错误的结论，排除亲子关系。为了找出这种现象的原因，用新引物重新扩增,然后进行大片段Sanger测序。我们在两个样品中都发现了G到G/T的变化，该变化与核心重复的3'末端相距59个碱基。这可能被认为是引物结合区处的新变体,其尚未被报道导致无效等位基因的出现。我们还发现，在D2S1338的上游和下游序列中，存在多个单核苷酸多态性（SNP），其次要等位基因频率（MAF）大于0.1。当设计用于扩增D2S1338的引物时,应考虑并避免这些SNP的可能的不利结果。
