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犯罪现场调查之法医DNA分析技术

发布: 2016-01-16 2,740阅读 201评论

在各色各样的探案类型电视剧中，除了思维敏锐、身手不凡的探长外，都或多或少有提到一个叫“法医法证（Forensics）”的部门。法医法证的技术人员用各种方法从犯罪现场寻找、分析犯罪分子留下的蛛丝马迹，并为探长们辨别疑犯、抓捕罪犯提供方向或证据。最常用的就是法医DNA分析技术（forensic DNA profiling）。

DNA存在于各种生物的细胞内, 因此理论上含有细胞的各种生物材料都可以进行法医DNA分析。从物证鉴定的角度可以分为四类：

  1. 人体的各种体液、组织、毛发及表皮脱落物；
  2. 各种动物细胞；
  3. 植物的根、茎、叶、花、果与种子；
  4. 细菌与真菌等微生物。

我们都知道DNA是遗传物质，而且DNA控制每个生物体的性状。那么自然地推测不同生物之间，或者同一物种不同个体之间，DNA序列应该有很多相同的部分，也有很多不同的部分。比如说，我们都有视觉，有相同种类的组织或器官，这些相同点一定是由DNA序列上相同的部分决定的；但是每个人都有自己的特点，不同的眼睛大小，不同的皮肤颜色，这些则是由DNA序列上不相同的部分控制的。

世界上没有一模一样的两个人，即使是双胞胎也会有不同的地方。这也就意味着，当对比个人与个人的基因组时，总可以发现DNA序列的差异，这种差异被称之为DNA的多态性。你的基因组就好比是自己的一个号码，世上没有任何一个人和你有相同的号码。当DNA多态性运用在犯罪辨识上时，我们可以取样犯罪现场留下的DNA证据，然后拿它们去比对疑犯的DNA，最终确定哪名疑犯才是真正的犯罪分子。DNA作为证据，因为有超高的识别率，所以在现代法庭是被接受的。

 

那么，问题来了，到底哪些DNA差异是能够被分析的，又是怎么被分析的？

 

RFLP遗传标记分析

RFLP(Restriction Fragment Length Polymorphism)，又称之为限制性片段长度多态性。我们的基因组被酶切后，产生一条条大小不等的片段，每个人的基因组可以产生的片段都可能是不一样长短的。这种方法的辨别力度是106-108（对比两人各六条片段的长短）。RFLP分析技术是由SirAlec Jeffreys研发的，此人是当代DNA指纹系统的奠基人，可以说是相当的厉害。

 

STR遗传标记分析

STR（ShortTandem Repeats），短串联重复序列。STR是均匀分布在基因组中的简单重复序列。到目前为止，在人类基因组中，已经发现的STR位点有8000多个。每个人在特定的STR位点，可能会拥有不同重复长度的序列。运用基因测序的方法，我们可以标记一个人基因组中的某几个STR位点的长度和碱基组成。这种分析方法的辨别力度是1014-1023，而全世界人口数是109，STR分析结果基本不会有误差，每个人都有自己特定的STR分布。


除了上面说的两种分析方法外，还有SNP单核苷酸多态性分析，RAPD随机引物扩增多态性分析等等，在此，小编就不多做解释了。

专有名词解释来自维基百科,图片来自网络，内容由BioEngX原创，转载请注明！

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