Department of Forensic Medicine, Nanjing Medical University, Nanjing, Jiangsu, 211166, PR China.
Department of Forensic Medicine, Nanjing Medical University, Nanjing, Jiangsu, 211166, PR China.
Forensic Sci Int Genet. 2019 May;40:140-149. doi: 10.1016/j.fsigen.2019.02.018. Epub 2019 Feb 22.
Massively parallel sequencing (MPS) technology enables the simultaneous analysis of different kinds of forensic genetic markers as well as the detection of the alleles with minor contributions in a highly unbalanced DNA mixture. In our previous study, we presented a novel set of microhaplotype loci and evaluated their application value in analyzing the DNA mixtures. However, several issues remain unclear, for example (i) whether the major or the minor donor in an unbalanced DNA mixture can be compared with a known suspect, (ii) whether the proportion of each contributor in a DNA mixture can be inferred, (iii) whether the captured alleles can be assigned to the major or the minor donor. To further address these issues, during the present study, we increased the number of loci in a single multiplex system to 25 (all the microhaplotypes have a length less than 50 bp). The DNA samples of 60 unrelated Han Chinese individuals, 40 artificially made DNA mixtures with different mixing proportions were analyzed with MPS by using the microhaplotypes panel. By comparing the population genetic data of the 25 microhaplotypes in 26 populations from 1000 Genome Project (1000 G), the microhaplotypes were found to have similar high A values in different populations. The likelihood ratios were further employed to compare the mixtures and known suspects. The major contributor could be well identified in both balanced and unbalanced samples. The minor contributor could also be identified if capturing enough loci. When we divided the microhaplotypes into different subgroups, significant correlation was found between the allele depth ratio and the gradual mixing ratios. The allele depth patterns in balanced, mildly imbalanced and severely imbalanced mixtures were clarified, and we found that certain loci could be discriminated from the contributors and they could be used for direct individual identification.
高通量测序（MPS）技术能够同时分析不同类型的法医遗传标记，并在高度不平衡的 DNA 混合物中检测具有较小贡献的等位基因。在我们之前的研究中，我们提出了一套新的微单倍型基因座，并评估了它们在分析 DNA 混合物中的应用价值。然而，仍有几个问题尚不清楚，例如：（i）在不平衡的 DNA 混合物中，主要供体还是次要供体可以与已知嫌疑人进行比较；（ii）能否推断 DNA 混合物中每个供体的比例；（iii）能否将捕获的等位基因分配给主要供体还是次要供体。为了进一步解决这些问题，在本研究中，我们将单个多重体系中的基因座数量增加到 25 个（所有微单倍型的长度均小于 50bp）。使用微单倍型面板，通过 MPS 对 60 个无关汉族个体的 DNA 样本和 40 个不同混合比例的人工 DNA 混合物进行了分析。通过比较 26 个人群的 25 个微单倍型的群体遗传数据（来自 1000 基因组计划（1000G）的 26 个人群），发现这些微单倍型在不同人群中具有相似的高 A 值。进一步使用似然比来比较混合物和已知嫌疑人。在平衡和不平衡的样本中，主要供体都可以很好地识别。如果捕获足够的基因座，也可以识别次要供体。当我们将微单倍型分为不同的亚组时，发现等位基因深度比与逐渐混合比之间存在显著相关性。阐明了平衡、轻度不平衡和严重不平衡混合物中的等位基因深度模式，发现某些基因座可以从供体中区分出来，并可用于直接个体识别。
