The use of a tunable light source (Mini-Crimescope MCS-400, SPEX Forensics) in dissecting microscopic detection of cryptic epithelial particles

As skin particles are often deposited by even a single skin contact, the detection of skin debris is important for evidence collection and DNA testing. Unfortunately, even when a dissecting microscope is used by an experienced examiner, epidermal particles are often hard to find and these traces of evidence might escape DNA analysis. Fluorescence is defined as the property of absorbing short-wavelength light and emitting longer-wavelength light. By virtue of the fluorescence characteristics of many target materials, tunable light sources assist in the macroscopic search of crime scenes and items. We combined the dissecting microscope and an alternate light source to examine the fluorescence characteristics of skin and skin particles. In a comparative study, small skin scales were hidden between sand, fibers, and soil probes, and it proved possible to search more successfully with less time and effort. On staged casework exhibits, the efficiency of the screening aid was again tested and the usability of the new procedure shown.     

Simplified low-copy-number DNA analysis by post-PCR purification

Frequently, evidentiary items contain an insufficient quantity of DNA to obtain complete or even partial DNA profiles using standard forensic gentotyping techniques. Such low-copy-number (LCN) samples are usually subjected to increased amplification cylces to obtain genetic data. In this study, a 28-cycle polymerase chain reaction (PCR) was used to evaluate various methods of post-PCR purification for their effects on the sensitivity of fluorophore-based allelic detection subsequent to capillary electrophoretic separation. The amplified product was purified using filtration, silica gel membrane, and enzyme mediated hydrolysis purification techniques and evaluated for their effect on fluorescent allelic signal intensity. A purification method was selected and its effect on fluorescent allelic signal intensity was compared with that of the unpurified PCR product. A method of post-PCR purification is described which increases the sensitivity of standard 28-cycle PCR such that profiles from LCN DNA templates (<100 pg DNA) can be obtained. Full DNA profiles were consistently obtained with as little as 20 pg template DNA without increased cycle number. In mock case type samples with dermal ridge fingerprints, genetic profiles were obtained by amplification with 28 cycles followed by post-PCR purification whereas no profiles were obtained without purification of the PCR product. Allele dropout, increased stutter, and sporadic contamination typical of LCN analysis were observed; however, no contamination was observed in negative amplification controls. Post-PCR purification of the PCR product can increase the sensitivity of capillary electrophoresis to such an extent that DNA profiles can be obtained from <100 pg of DNA using 28-cycle amplification.     

Allele frequencies of 15 autosomal STR loci in the Iraq population with comparisons to other populations from the middle-eastern region

Allele frequencies for the 15 autosomal STR loci included in the AmpFlSTR((R)) IdentifilerTM PCR Amplification Kit panel from Applied Biosystems (D3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820, TH01, TPOX, CSF1PO, D19S433, D2S1338, D16S539) and several statistical parameters were estimated from a sample of 103 unrelated individuals, mostly Shia and Sunni Arabs, living in most of central and southern Iraq provinces. We compared the allele frequency spectrum detected in the Iraqi population to allele frequencies from 11 other data sets from published studies of individuals from Turkey, Iraqi-Kurdistan, Saudi Arabia, Arab Emarates, Oman, Iran, Syria, and Jordan. Significant global differences in allele frequencies were detected in 9 of the 11 comparisons following sequential Bonferroni corrections. Comparisons with the two independent panels from Saudi Arabia were not significant after applying Bonferroni corrections, however, low P-values (P<0.05) associated with these two contrasts nonetheless suggested that at least slight genetic differences between populations may exist.     

Nucleotide variability of HV-I in Afro-descendents populations of the Brazilian Amazon Region

The analysis of genetic variation in the nucleotide sequences of mitochondrial DNA, provides unique information about the population diversity and human identification. In this study, the mitochondrial DNA sequences of the first hypervariable region (HV-I) were analyzed in 243 unrelated individuals of seven Afro-descendents populations of the Amazon Region. Sequence polymorphisms were detected using PCR and direct sequencing analysis. A total of 133 different haplotypes were found determined by 97 variable nucleotides. Each one of the three more frequent haplotypes was shared by 9 samples and 91 sequences were unique. The genetic diversity was estimated to 0.9898+/-0.0016 and the probability of two random individuals showed identical mitochondrial DNA (mtDNA) haplotypes were 1.2%.     

单核苷酸多态性与法医学DNA分型技术

单核苷酸多态性(single nucleotide polymorphism,SNP)分型技术越来越成为法医学领域关注的热点,它在研究Y染色体或线粒体单倍型以及DNA表型的分析中具有重要应用价值。本文着重比较分析了SNP技术与片段长度多态性技术之间的优劣,同时就当前STR位点识别概率与所需选择的SNP位点数进行探讨。此外,本文还就各类SNP分型方法的优缺点及其法医学应用进行了论述。     

MiniFiler试剂盒运用于法医微量物证的检验

目的应用MiniFiler试剂盒对法医微量物证进行DNA分析。方法采用MiniFiler试剂盒对样本进行DNA分型,确定样本9个STR基因座的等位基因型。结果10pg DNA模板经MiniFiler试剂盒扩增后,能够进行DNA分型,但40pg以上的DNA方可得到稳定可靠的分型结果。结论MiniFiler试剂盒可以用于法医微量物证的STR分析。     

人骨骼肌线粒体DNA4977片段缺失与年龄的相关性调查

目的 探讨人骨骼肌组织中线粒体DNA 4977bp片段的缺失情况及其与年龄的相关性.方法 收集105例不同年龄死者的骨骼肌组织,抽提MDT,通过CPR、琼脂糖紫外凝胶成像等技术,测定不同年龄组线粒体DNA 4977bp片段的缺失情况.结果 在105例样品中,不同年龄组(0～9、10～19、20～29、30～39、40～49、50～59、60～69、70～79、80～89、90～99岁)mtDNA4977片段缺失的频率分别为:0、0、0.003%、0.011%、0.015%、0.033%、0.038%、0.062%、0.069%、0.091%.结论 人骨骼肌线粒体DNA 4977bp片段的缺失频率随着年龄的增长而增高,各年龄组之间具有显著差异(P《0.01).该缺失片段的检测对于软组织年龄推测具有一定指导意义.     

A Study of PCR Inhibition Mechanisms Using Real Time PCR*,†

Abstract: In this project, real time polymerase chain reaction (PCR) was utilized to study the mechanism of PCR inhibition through examination of the effect of amplicon length, melting temperature, and sequence. Specifically designed primers with three different amplicon lengths and three different melting temperatures were used to target a single homozygous allele in the HUMTH01 locus. The effect on amplification efficiency for each primer pair was determined by adding different concentrations of various PCR inhibitors to the reaction mixture. The results show that a variety of inhibition mechanisms can occur during the PCR process depending on the type of co‐extracted inhibitor. These include Taq inhibition, DNA template binding, and effects on reaction efficiency. In addition, some inhibitors appear to affect the reaction in more than one manner. Overall we find that amplicon size and melting temperature are important in some inhibition mechanisms and not in others and the key issue in understanding PCR inhibition is determining the identity of the interfering substance.     

Integrated DNA and Fingerprint Analyses in the Identification of 60‐Year‐Old Mummified Human Remains Discovered in an Alaskan Glacier

Abstract: This report describes the identification of a merchant mariner who perished in 1948 when Northwest Airlines Flight 4422, a DC‐4 carrying 24 seamen and six crew members crashed into Mount Sanford, Alaska. Fifty‐one years later, a human forearm and hand were found close by the wreckage of the plane, prompting identification efforts using DNA and fingerprints. There were significant challenges to both the fingerprint and DNA analyses. The hand was badly desiccated, making fingerprint friction‐ridge detail almost invisible and the remains had been embalmed upon discovery, making DNA amplification difficult. We present the results of an interdisciplinary approach that successfully addressed these challenges and ultimately led to the identification of the remains. These efforts relied on efficient fingerprint rejuvenation and imaging techniques that improved print resolution, as well as new DNA extraction techniques optimized for aggressively embalmed remains.