表观遗传学及其在同卵双生子研究中的新进展

表观遗传学是指不改变DNA序列的可遗传的基因表达改变.是多细胞真核生物的重要生物学现象.DNA甲基化、基因组印记、组蛋白乙酰化、组蛋白甲基化、染色质重塑、假基因和小分子RNA等是表观遗传学的主要研究内容.同卵双生子(monozygotic twins,MZ)是由一个受精卵分裂发育而成的双胞胎,二者具有完全相同的基因组DNA序列.从经典遗传学的角度,使用短串联重复序列(short tandem repeat,sTR)和单核苷酸多态性(single nucleotide polymorphism,SNP)等遗传标记均不能对其进行有效的个体甄别.因此,寻找新的遗传标记显得尤为重要,最新表观遗传学领域的研究成果表明.MZ个体间DNA甲基化差异显著,这为甄别MZ个体提供了新的策略.本文对表观遗传学的概念、研究内容及表观遗传学在MZ鉴别中的应用前景进行了综述.     

DNA甲基化在法医DNA分析中的应用

表观遗传学在生命的发生、发展过程中起着十分重要的作用。DNA甲基化作为表观遗传的一个重要方面,不仅参与多种基因的表达调控,与机体的发育、肿瘤发生等密切相关,而且具有可遗传性、相对稳定性、亲缘特异性、基因组中含量丰富等特点,已证实适用于法医DNA分析。本文对近年来DNA甲基化在印迹基因、同卵双生子鉴定、年龄、性别推断方面的研究与应用进行回顾与综述,以期为在法医学及相关领域中应用提供参考。     

DNA甲基化在组织/体液来源鉴定中的研究进展

对可疑生物样本的组织/体液进行来源鉴别是重建犯罪现场、推断犯罪性质等侦查活动中极为重要的一环。对表观遗传学理论的研究证明运用基因组中存在的组织特异性DNA甲基化差异位点(t DMRs)可以对组织/体液进行来源鉴别。本文旨在通过对近年来DNA甲基化在法医学领域用于鉴定人体组织/体液来源方面的研究成果进行阐述,试图用所得到的信息来分析DNA甲基化作为一种组织/体液鉴定遗传学标记的可能性、优劣点及其应用价值和发展前景,以期能为法医工作者的相关研究及实践提供参考。     

线粒体DNA研究进展

人类细胞内存在两套基因组,一套是细胞核内的基因组,即核DNA(nuclear DNA,nDNA);另一套是位于细胞质线粒体内的基因组,即线粒体DNA(mitochondrial DNA,mtDNA).由于线粒体在生命活动中的重要作用及其基因组自身特点,使得mtDNA在细胞遗传学、分子遗传学、发育遗传学和法庭科学等领域受到了广泛重视.     

DNA甲基化与年龄推断

年龄推断是法医学研究的重要内容。近年来表观遗传学研究发现,基因组DNA甲基化总体水平随年龄增加而降低,同时部分位点的甲基化水平却随年龄增加而升高。通过检测DNA甲基化水平,构建与之相关的年龄变化模型,可用于推断个体年龄。本文对DNA甲基化与个体年龄的相关性、适用于法医学领域的检测方法及其在法医学年龄推断方面的应用前景进行综述,希望能为相关研究和应用提供参考。     

DNA甲基化标记检测方法及其法医学应用

DNA甲基化是重要的表观遗传修饰,主要在转录水平上调控基因的表达。DNA甲基化在人类基因组中含量丰富、分布广泛;甲基化谱有时空特异性、细胞特异性和亲源特异性。新近研究表明DNA甲基化在组织体液鉴定、同卵双生子鉴定、年龄推断、性别推断和亲子鉴定等方面具有一定的应用价值,有望成为一种新的法医学遗传标记。本文就DNA甲基化检测方法的研究进展及法医学应用进行综述,以期为法医学实践提供参考。     

DNA甲基化及其与个体年龄相关性研究

近年来表观遗传学研究发现,基因组DNA甲基化总体水平随年龄增加而降低,同时部分位点的甲基化水平却随年龄增加而升高。本文重点介绍了DNA甲基化与年龄的相关性及其在年龄推断方面的研究进展,旨在为法医学个体年龄推断的研究提供一种新的思路。     

生物信息学在法医学中的应用与展望

自DNA指纹技术应用于司法实践的报道以来,法医DNA分析发挥着越来越重要的作用。近年来,随着基因组学高通量测序技术的快速发展,生物信息学分析手段也逐渐开始与法医学应用结合,极大地扩展了法医物证的分析能力。本文综合阐述了法医遗传学所涉及的基因组、表观组以及转录组生物信息分析相关研究现状以及发展趋势。     

法医SNP系谱推断技术研究进展

法医SNP系谱推断技术是利用基因组中的高密度SNP数据，基于血缘同源片段长度分析等算法，推断远亲缘关系的一种新型侦查技术手段。与传统STR亲缘关系鉴定方法相比，法医SNP系谱推断技术可以分析更远的亲缘关系，且可以在社会公共DNA数据库中进行家族关系搜索，应用场景更为广阔，包括犯罪嫌疑人查找、受害者的身源鉴定、失踪人口寻找等。本文就法医SNP系谱推断技术的遗传学原理、高密度SNP分型技术、常用的推断算法以及在低质量DNA中的应用等方面的研究进展进行阐述，以期为该技术应用时选择合适的检测技术和亲缘关系分析算法提供思路。     

Alu家族在法医DNA分析中的应用

Alu家族是灵长类特有的短散在重复序列,在人类基因组内含量丰富,分布广泛,甲基化程度高,有种属特异性和插入变异,为法医DNA分析面临的许多问题提供了潜在的解决途径。目前,Alu元件在法医DNA分析中的应用包括:DNA定量、种属鉴定、种族鉴定、性别鉴定、个体识别和亲子鉴定,以及全基因组扩增等。本文总结各种基于Alu元件的法医DNA分析技术的原理和特点,探讨Alu元件的法医学研究和应用前景,供相关学者参考。     

单亲案的亲权概率的计算及认定标准

确定单亲案的亲权概率计算方法和认定标准。用多基因座DNA分析方法和计算多基因座累积平均非父排除率计算公式。检测8个以上的DNA多态性基因座,在等位基因的遗传不违反孟德尔规律的前提下,父权概率都可达到或超过0.9990的标准;对不存在亲生关系的案例,在用本方法时,都有3个或更多的基因座的等位基因遗传违反孟德尔规律。对单亲案的亲权鉴定,检测的多态性基因座要在8个以上。在肯定亲生关系时,父权概率要达到或超过0.9990;在否定亲生关系时,必须有3个以上或更多的基因座违反孟德尔遗传规律。     

亲权鉴定若干问题综述

对亲权鉴定中遗传标记的研究历史及现状进行了综述，并对国际法医遗传学会亲子鉴定委员会关于DNA生物计算的建议进行了解读。     

Combination of DNA-based and conventional methods to detect human leukocyte antigen polymorphism and its use for paternity testing

In cases of disputed paternity, the scientific goal is to promote either the exclusion of a falsely accused man or the affiliation of the alleged father. Until now, in addition to anthropologic characteristics, the determination of genetic markers included human leukocyte antigen gene variants; erythrocyte antigens and serum proteins were used for that reason. Recombinant DNA techniques provided a new set of highly variable genetic markers based on DNA nucleotide sequence polymorphism. From the practical standpoint, the application of these techniques to paternity testing provides greater versatility than do conventional genetic marker systems. The use of methods to detect the polymorphism of human leukocyte antigen loci significantly increases the chance of validation of ambiguous results in paternity testing. The outcome of 2384 paternity cases investigated by serologic and/or DNA-based human leukocyte antigen typing was statistically analyzed. Different cases solved by DNA typing are presented involving cases with one or two accused men, exclusions and nonexclusions, and tests of the paternity of a deceased man. The results provide evidence for the advantage of the combined application of various techniques in forensic diagnostics and emphasizes the outstanding possibilities of DNA-based assays. Representative examples demonstrate the strength of combined techniques in paternity testing.     

Paternity determination when the alleged father's genotypes are unavailable.

In paternity testing using the DNA evidence, analysis of the deficiency case when the DNA profiles of the alleged father are not available is different from that of the case with complete evidence. In this paper, we describe how to evaluate and determine the paternity in the deficiency case, by comparing the paternity indexes of the true father and the falsely non-excluded man.     

The 1998-1999 collaborative exercises and proficiency testing program on DNA typing of the Spanish and Portuguese Working Group of the International Society for Forensic Genetics (GEP-ISFG)

A total of 28 laboratories (labs) submitted results for the 1998 collaborative exercise and the proficiency testing program of the Spanish and Portuguese Working Group of the International Society for Forensic Genetics (GEP-ISFG) group. This number increased to 46 labs in 1999. Six bloodstains were submitted, each one with 200 microl soaked in cotton except the sample no. 6 submitted for DNA quantification which had 2 microl. One of the samples was a mixed stain. A paternity testing case and a criminal case in the 1998 trial (GEP'98) and two paternity testing cases in 1999 (GEP'99) were included and the statistical evaluation of the evidence was requested in both cases. In the GEP'99 trial, a theoretical paternity testing case was included. A total of 52 DNA genetic markers were used by the participants in the GEP'98 trial, which increased to 101 in GEP'99. Despite this increasing number of participating labs, results remained quite satisfactory. All the labs used PCR-based DNA polymorphisms with an increasing number of markers, obtaining good results. SLPs were used by a decreasing number of labs but the results indicated a good level of expertise despite the different protocols used.Good results were also obtained for mtDNA despite the difficulties presented by the samples due to the presence of length heteroplasmy in some samples in both trials. The detection of heteroplasmy should, however, be improved.Similar conclusions were reached for both, the paternity and the criminal case by all the labs. Common methodologies for the statistical evaluation of the paternity case were used and the paternity index and the probability of paternity (with an a priori value of 0.5) reported by most of the labs. Also, a great uniformity was found in the evaluation of the criminal case despite the lack of a specific hypothesis in the design of the exercise. Some errors in statistical programs or in calculations were detected in a theoretical paternity case included in the GEP'99 trial for statistical analysis.     

D18S51及其侧翼区3个SNP组成的SNP-STR在亲子鉴定中的应用

目的将一个单倍型区块内的遗传标记单核苷酸多态性(SNP)和短串联重复序列(STR)组成SNPSTR单倍型,调查其在成都汉族人群中的分布,并探讨其在特殊亲子鉴定案例中的应用价值。方法选取DNA联合索引系统(combined DNA index system,CODIS)中突变率较高的基因座D18S51,与其侧翼区的3个SNP位点(rs8089331、rs8094489、rs7236090)组成SNP-STR,通过巢式等位基因特异性PCR的方法获得SNP-STR单倍型,调查该单倍型在75名成都汉族人群中的分布,并应用于两例D18S51基因座不符合遗传规律的二联体亲子鉴定案件。结果成功建立SNP-STR分型方法,在成都汉族人群中共发现43种单倍型,多态性为0.948 6,并成功解决了两例二联体亲子鉴定案件。结论 SNP-STR具有良好的多态性,有望应用于特殊的亲缘关系鉴定。     

Establishing paternity using minisatellite DNA probes when the putative father is unavailable for testing

A paternity case involving a putative father who had died a few years earlier in an automobile accident was referred to the laboratory for testing. The child and his mother, the deceased's parents, and nine of the deceased's siblings were available for analysis. As previously reported, paternity testing using red blood cell groups, human leukocyte antigens (HLA), red blood cell enzymes, serum proteins, and immunoglobulin allotypes gave a cumulative paternity index of 43,300 and a combined probability of paternity equal to 99.998%. RFLP analysis using Hinf I and Sau 3A single digests and the minisatellite deoxyribonucleic acid (DNA) probes 15.1.11.4 and 6.3 showed no exclusion of paternity and gave nearly conclusive evidence that the putative father was the biological father of the child.     

PowerPlex~(TM) 16体系在亲子鉴定中的应用评估

目的 评估PowerPlexTM16体系在亲子鉴定中的检验能力。方法 以633例亲子鉴定案例为基础,调查PowerPlexTM16体系15个STR基因座的群体遗传学数据资料,并对该体系在亲子鉴定中的排除能力及遗传稳定性进行评估。结果 879名无关个体共检出197个等位基因,739种基因型,累计个体识别力为1×10-30,累计非父排除率为0.999999999999987。633例亲子鉴定案件中有95例确定为排除亲权,平均排除指标为6个。18例表现出1个STR基因座突变的现象,1例表现出2个STR基因座突变的现象。结论 PowerPlexTM16体系应用于亲子鉴定是高效、可靠的。     

A case of tri-allelic pattern at locus D3S1358 on chromosome 3p21 inherited from paternal grandmother

We are reporting a case of tri-allelic inheritance at locus D3S1358 commonly used for genetic identification in forensic DNA testing. This case was encountered during routine paternity testing using commercial DNA profiling kits. The tri-allelic inheritance identified was probably a result of duplication at this locus, supported by the equal peak intensities and inheritance pattern from grandparent to child.     

On statistical analysis of forensic DNA: theory, methods and computer programs

Statistics plays an important role in evaluating the evidential weight of forensic DNA. In this paper, general statistical principles for forensic DNA analysis are presented. We introduce the theory and methods for the statistical assessment in kinship determination and DNA mixture evaluation. In particular, analytical formulas for testing for biological relationship among three individuals and for assessing the DNA mixture evidence in the case of multiple subdivided ethnic groups are developed. Two user-friendly computer programs are demonstrated to exhibit their wide applicability in tackling with complex kinship/paternity and mixture problems. The EasyDNA program can solve a complicated paternity case in 1 min.