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随着科技的进步,一些犯罪案件的科技含量也在提高,手段也在不断多样化,并且常规物证被有意识地销毁,往往给侦破工作带来难度,因此微量物证尤其是生物检材越来越引起物证工作者的重视. 2011年公安部关于《公安机关侦办命案工作规范》中要求,外围现场和关联现场要受到重视,尽可能多地发现并提取有用价值的物证,尤其是微量物证和生物检材.植物是犯罪现场中一种重要的环境和过程证据,而且很多案件中常常出现植物类物证,这些植物类物证大多都无法用形态学检验方法来鉴别,需要借助植物DNA技术手段对植物物证的来源和种类进行鉴定.这对于查找破案线索、划定侦查范围和方向提供了有价值的证据,也为法庭诉讼产生重要的指导和支撑作用[1-2].近年来,CBOL(生物条形码协会)植物工程组对约550个物种进行通用引物筛选,试图用一个或组合的DNA条形码来鉴别植物物种,这些研究成果已在鉴别违禁植物、毒品、出入境物种资源等方面得到应用[3].植物物证个体识别方面的研究报道不多,虽然也有用传统DNA分子标记技术进行DNA多态性比对分析,进行同一认定的成功案列,但该方法难以实现自动化,检测方法相对缓慢而且费力.目前,利用RAD-seq技术来进行植物物证的个体识别还未见报道.
简化基因组测序是在第二代测序技术基础上发展起来的,是利用酶切技术、序列捕获芯片技术或其他实验手段降低物种基因组复杂程度,针对基因组特定区域进行测序,进而反映部分基因组序列结构信息的综合实验技术[4],目前运用较广泛的方法是限制性酶切相关位点的DNA测序(Restriction Association site DNA sequencing,RAD-seq)[5]. RAD-seq所得的全基因组范围特异酶切位点附近的小片段DNA标签,能较好地代表整个基因组的序列特征,从而能够在大多数生物中获得成千上万的单核苷酸多态性(Single Nucleotide Polymorphism,SNP)标记. RAD-seq技术操作简单,不受参考基因组限制,并可简化复杂基因组,目前已广泛应用于分子育种、系统进化、种质资源等领域[6-8],但在植物物证个体识别方面,RAD-seq应用于法庭科学中具体的实验实施和分析方法还需要摸索细化.
桂花Osmanthus sp.在重庆地区分布很广,在公园、路边、居民区随处可见,桂花可以年年开花结果,且花期较长,与我们的日常生活紧密联系,如果涉案出现的可能性较大.本文的研究对象选择没有可参考基因组的桂花作为植物物证个体识别的样本,利用简化基因组测序技术来降低基因组测序和分析的复杂度,进而构建植物物证桂花样品的个体识别数据库,试图找到能识别植物物证样品桂花同一个体的方法,为后续利用RAD-seq技术进行植物类物证的个体鉴别提供可靠的方法和支持.
Application of RAD-seq Technology in Individual Identification of Plant Material Evidence
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摘要: 在犯罪案件现场发现与嫌疑人(或受害人)相关联的植物物证,鉴定它们来源和进行个体识别,可为案件的调查取证提供有价值的证据或线索.该研究采用一种RAD-seq技术对18个桂花样品(15个已知样本、3个盲测样本)进行DNA建库和高通量测序,序列多态性分析,评估其遗传多样性,并用基于SNP和基于k-mer频谱的2种比较分析方法探讨了RAD-seq数据用于个体识别的科学性和对植物物证进行同一性认定的可行性.结果表明,2种方法都能成功识别3个盲测样本.相比较而言,基于k-mer频谱的方法在稳定性和自动化程度上要优于基于SNP亲缘关系树的分析方法,更易推广到公安物证鉴别应用中. RAD-seq技术结合该文的分析方法能够识别出未知植物物证样品A,B和C分别对应于植物物证桂花1,4和11,实现了对案件中关联植物物证进行精确检验鉴定的方法和一个小型鉴定实例,但其识别能力有待扩展到更大样本集和更多物种中.Abstract: Plant evidence related to the suspect/victim found at the crime scene can provide valuable evidence or clues for investigation and evidence collection of the case. In a study reported in this paper, an RAD-seq (restriction-site associated DNA sequencing) technique was used to build a database and make high-throughput sequencing for 18 samples of Osmanthus (15 known samples and 3 blind samples), analyze their sequence polymorphism and evaluate their genetic diversity. Two kinds of comparative analysis method, one based on SNP (single nucleotide polymorphism) and the other on k-mer spectrum, were employed to discuss the scientific nature of RAD-seq data for individual identification and the feasibility of identity identification of plant material evidence. The results showed that both methods could successfully identify the three blind samples. Comparatively, the k-mer spectrum-based method was superior to the analysis method based on the SNP genetic relationship tree in stability and automation degree. It was easier to apply to the public security material evidence of identification. In conclusion, the RAD-seq technology used in combination with the analysis method successfully identified the three unknown plant material evidence samples A, B and C, and they corresponded to the sweet scented osmanthus 1, 4 and 11, respectively. It has provided a method for accurate examination and identification of related plant material evidence in a case and a small identification example, but its ability of identification is to be extended to a larger set of samples and more plant species.
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Key words:
- plant evidence /
- RAD-seq /
- SNP /
- individual identification /
- Osmanthus sp. .
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表 1 过滤数据量统计表
样本 过滤后的reads数 过滤后的碱基数 Osmanthus sp. 1 1,930,652 362,962,576 Osmanthus sp. 2 1,644,692 312,491,480 Osmanthus sp. 3 1,656,527 308,114,022 Osmanthus sp. 4 1,606,295 295,558,280 Osmanthus sp. 5 2,758,437 518,586,156 Osmanthus sp. 6 2,791,362 530,358,780 Osmanthus sp. 7 3,662,058 681,142,788 Osmanthus sp. 8 353,502 65,044,368 Osmanthus sp. 9 1,748,449 328,708,412 Osmanthus sp. 10 1,558,440 296,103,600 Osmanthus sp. 11 2,013,516 374,513,976 Osmanthus sp. 12 1,265,587 232,868,008 Osmanthus sp. 13 2,002,268 376,426,384 Osmanthus sp. 14 1,960,908 372,572,520 Osmanthus sp. 15 2,260,074 418,308,332 Osmanthus sp. A 1,895,016 356,263,008 Osmanthus sp. B 1,960,789 372,549,910 Osmanthus sp. C 2,354,668 436,015,002 总计 35,423,240 6,638,587,602 表 2 经过滤所得的SNP信息
样本 总SNP 纯合的SNP 纯合率/% 杂合SNP 杂合率/% Osmanthus sp. 1 93,463 75,897 81.21 17,566 18.79 Osmanthus sp. 2 77,768 61,304 78.83 16,464 21.17 Osmanthus sp. 3 80,994 62,544 77.22 18,450 22.78 Osmanthus sp. 4 39,629 6,529 16.48 33,100 83.52 Osmanthus sp. 5 83,420 66,103 79.24 17,317 20.76 Osmanthus sp. 6 63,774 52,570 82.43 11,204 17.57 Osmanthus sp. 7 68,167 55,654 81.64 12,513 18.36 Osmanthus sp. 8 3,373 2,835 84.05 538 15.95 Osmanthus sp. 9 158,467 129,413 81.67 29,054 18.33 Osmanthus sp. 10 127,311 101,440 79.68 25,871 20.32 Osmanthus sp. 11 125,369 102,350 81.64 23,019 18.36 Osmanthus sp. 12 61,719 50,821 82.34 10,898 17.66 Osmanthus sp. 13 69,229 56,272 81.28 12,957 18.72 Osmanthus sp. 14 65,116 53,650 82.39 11,466 17.61 Osmanthus sp. 15 79,286 64,002 80.72 15,284 19.28 表 3 未知植物物证样品A,B,C的SNP位点信息与桂花数据库比对的结果
样本 A B C 符合数 符合度 符合数 符合度 符合数 符合度 Osmanthus sp. 1 148 12.52% 86 7.28% 25 2.12% Osmanthus sp. 2 116 9.81% 94 7.95% 37 3.13% Osmanthus sp. 3 120 10.15% 87 7.36% 39 3.30% Osmanthus sp. 4 107 9.05% 116 9.81% 41 3.47% Osmanthus sp. 5 116 9.81% 86 7.28% 41 3.47% Osmanthus sp. 6 121 10.24% 98 8.29% 34 2.88% Osmanthus sp. 7 118 9.98% 96 8.12% 33 2.79% Osmanthus sp. 8 12 1.02% 7 0.59% 6 0.51% Osmanthus sp. 9 118 9.98% 85 7.19% 38 3.21% Osmanthus sp. 10 123 10.41% 90 7.61% 34 2.88% Osmanthus sp. 11 34 2.88% 38 3.21% 112 9.48% Osmanthus sp. 12 89 7.53% 64 5.41% 62 5.25% Osmanthus sp. 13 87 7.36% 76 6.43% 62 5.25% Osmanthus sp. 14 79 6.68% 68 5.75% 66 5.58% Osmanthus sp. 15 88 7.45% 66 5.58% 63 5.33% -
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