基于大规模并行测序技术探索新型遗传标记微单倍型在混合检材鉴定及族缘推断中应用价值的法医学研究

Mixed biological samples can be important evidences in criminal cases of sexual assault and violence. However, forensic identification of an individual in complex DNA mixtures remained unsolved. Besides, the Chinese National DNA Database covers only a small part of mainland population at present. When the suspect is not included, the value of its DNA extracted from crime scene is significantly reduced. Thus, obtaining ancestry information from the suspect’s DNA is of great value and significance to solving the cases. Microhaplotype is a new kind of genetic marker, which defined as a short DNA sequence containing two or more SNPs. These SNPs accomplish linkage inheritance as haplotypes and each haplotype constitute an allele. A microhaplotype locus could have up to 2^n alleles in theory (n = number of SNPs). Microhaplotype have both SNP’s advantages and unique value of high degree of polymorphism. Screening new microhaplotype loci and evaluating its application value in mixture identification and ancestry inference is an important subject. The present research aimed to establish a composite detection system based on massively parallel sequencing technology, through screening microhaplotype loci that are suitable for Chinese populations. And applying the system to the mixture identification and ancestry inference, to investigate its forensic value and provide basic research information.

混合生物检材在性侵害、暴力伤害等案件中是一种重要的生物物证，而混合生物检材的检验仍然是待解决的重大难题。此外，国内DNA数据库只覆盖小部分人群，当嫌犯的DNA数据不在库中时，其DNA分型价值明显降低，从DNA中获得族源信息，对侦查破案具有重要的价值。微单倍型是一种新型遗传标记，为包含2个或以上的单核苷酸多态位点的一段短DNA序列，将这些单核苷酸组成的不同单倍型作为该基因座的等位基因，理论上一个微单倍型位点可具有2^n个等位基因（n为单核苷酸多态个数）。微单倍型既有SNPs的优点，又有多态性高的独特优势，筛选新型微单倍型位点并评估其在混合生物检材鉴定和族源推断中的应用价值是一个重要的课题。本研究以大规模并行测序技术为基础，通过筛选适合于中国人群的微单倍型位点，建立复合扩增体系，并将之用于混合生物检材鉴定及族源信息推断，探索其在法医学中的应用价值，为解决法医个体识别相关问题提供基础研究资料。

混合生物检材是一种重要的生物物证，多见于性侵害、暴力伤害等刑事案件中，复杂混合生物检材的检验仍然是待解决的重大难题。传统的毛细管电泳技术，只能获得等位基因的片段长度和峰面积信息，相比之下，大规模并行测序能够得到等位基因的序列信息和测序深度，获取数据精度的提高使得大规模并行测序技术成为分析混合样本的理想手段。微单倍型一种新型遗传标记，具有分布范围广泛、位点数量多、序列结构简单、多态性高等优势，是适合于大规模并行测序技术的理想遗传标记。本研究从人类全基因组水平上筛选了适合个人识别和族源信息推断的微单倍型位点，建立了复合扩增体系，通过大规模并行测序技术对中国汉族人群进行了群体遗传学调查，获得了筛选出的微单倍型位点在中国汉族人群中的等位基因分布情况和法医学参数。通过构建标准化的混合样本模型，对平衡和不平衡混合样本、多人混合样本进行了测序分析。建立了机器学习模型，对混合样本测序结果进行整理和分析，结果表明通过分析混合样本中微单倍型基因座各个等位基因的测序深度、等位基因数目等数据可以帮助精确推断混合样本中供体人数，在不平衡检材中，根据不平衡的程度和基因型的组合，测序深度等，实现等位基因的拆分。本项目的研究成果表明微单倍型遗传标记结合大规模并行测序技术是分析混合样本，尤其是高度复杂的混合样本的理想手段。