Probabilistic expert systems for handling artifacts in complex DNA mixtures

This paper presents a coherent probabilistic framework for taking account of allelic dropout, stutter bands and silent alleles when interpreting STR DNA profiles from a mixture sample using peak size information arising from a PCR analysis. This information can be exploited for evaluating the evidential strength for a hypothesis that DNA from a particular person is present in the mixture. It extends an earlier Bayesian network approach that ignored such artifacts. We illustrate the use of the extended network on a published casework example.     

人权的普遍性根据与实现人权的文化前提

人的自由的绝对性使人拥有绝对的人权,维护与实践人权作为一种自觉的要求,要以对人的自由本质与绝对权利的自觉为前提,也就是要以启蒙文化为前提,而启蒙文化需要由文化启蒙来造就.这意味着,既不可能以武力推行人权,也不可能以任何文化传统的特殊性为借口拒绝人权.人权的绝对性与民族主义国家理论并无学理上的关联,一个主权实体内部的人权...     

The fate of the chemical warfare agent during DNA extraction

Forensic laboratories do not have the infrastructure to process or store contaminated DNA samples that have been recovered from a crime scene contaminated with chemical or biological warfare agents. Previous research has shown that DNA profiles can be recovered from blood exposed to several chemical warfare agents after the agent has been removed. The fate of four toxic agents, sulfur mustard, sodium 2-fluoroacetate, sarin, and diazinon, in a lysis buffer used in Promega DNA IQ extraction protocol was studied to determine if extraction would render the samples safe. Two independent analytical methods were used per agent, selected from GC-MS, 1H NMR, 19F NMR, (31)P NMR, or LC-ES MS. The methods were validated before use. Determinations were carried out in a semi-quantitative way, by direct comparison to standards. Agent levels in the elution buffer were found to be below the detectable limits for mustard, sarin, sodium 2-fluoroacetate or low (<0.02 mg/mL) for diazinon. Therefore, once extracted these DNA samples could be safely processed in a forensic laboratory.     

Identification and separation of DNA mixtures using peak area information

We introduce a new methodology, based upon probabilistic expert systems, for analysing forensic identification problems involving DNA mixture traces using quantitative peak area information. Peak area is modelled with conditional Gaussian distributions. The expert system can be used for ascertaining whether individuals, whose profiles have been measured, have contributed to the mixture. It can also be used to predict DNA profiles of unknown contributors by separating the mixture into its individual components. The potential of our probabilistic methodology is illustrated on case data examples and compared with alternative approaches. The advantages are that identification and separation issues can be handled in a unified way within a single probabilistic model and the uncertainty associated with the analysis is quantified. Further work, required to bring the methodology to a point where it could be applied to the routine analysis of casework, is discussed.     

高职高专实用英语口语教学研究

培养学生的英语应用能力是教育部高教司对高职高专教育英语教学的战略定位。本文分析了高职高专学生英语口语能力现状与《基本要求》教学目的之间存在的差距及产生这一差距的原因,并提出应从教、学、考三个方面来提高高职高专学生的英语口语能力。     

Y-STRs in forensic medicine: DNA analysis in semen samples of azoospermic individuals

ABSTRACT: The incidence of rape has increased, especially in metropolitan areas, such as the city of São Paulo. In Brazil, studies about it have shown that the majority of this type of crime is committed by the relatives and persons close to the victim. This has made the crime more difficult to be denounced, as only 10% of the cases are reported to competent police authorities. Usually, cytological exams are carried out in sex crime investigations. The difficulty in showing the presence of spermatozoa is frequent, but it does not exclude the presence of male DNA. The absence of spermatozoa in material collected from rape victims can be due to several factors, including the fact that the agressor suffers from azoospermia. This condition can be the result of a successful vasectomy. As the majority of DNA in the ejaculation sample is from spermatozoa, there is much less DNA to be analyzed. This study presents the application of Y‐STRs (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, and DYS393) in DNA analysis of sperm samples from 105 vasectomized men. The study demonstrated a great variation in DNA concentration. DNA extraction and amplification was possible in all sperm samples even in the absence of spermatozoa. The same profile was observed, for each individual, from DNA extracted from blood, pre‐ and postvasectomy semen samples. The use of markers specific for Y chromosome in sex crime cases, especially in the absence of spermatozoa, is very important, mainly because in most situations there is a small quantity of the agressor's DNA in the medium and a large quantity of the victim's DNA.     

Real-time polymerase chain reaction quantification of canine DNA

The accurate quantification of target DNA is an important step in the short tandem repeat analysis of forensic biological samples. By utilizing quantification data to control the amount of template DNA in the polymerase chain reaction (PCR), forensic scientists can optimize testing and minimize the consumption of limited samples. The ability to identify and quantify target DNA in mixed-species samples is crucial when it may be overwhelmed by nontarget DNA, as in cases of dog attack. We evaluated two quantitative real-time PCR assays for dynamic range, species specificity, and inhibition by humic acid. While both assays proved to be highly sensitive and discriminating, the Melanocortin-1 Receptor (MC1R) gene Taqman assay had the advantages of a shorter run time, greater efficiency, and safer reagents. In its application to forensic casework, the MC1R assay has been advantageous for quantifying dog DNA in a variety of mixed-species samples and facilitating the successful profiling of individual dogs.     

Mitochondrial DNA amplification success rate as a function of hair morphology

This study examines the amplification success rate of mitochondrial DNA from human head hair with respect to their potential for forensic application. Mitochondrial DNA was isolated using a Chelex-based extraction method and amplified using the LINEAR ARRAY duplex PCR system. The particular focus of this study was to characterize the morphological features of human head hair in order to further the understanding of the factors that influence amplification success rate in hair tissue using the LINEAR ARRAY duplex PCR system. 2554 head hairs from 132 individuals representing four population groups were amplified. The hair samples were characterized as follows: 1251 were identified microscopically as telogen hairs and 1303 were classified as hairs without roots (removed before extraction). Amplification success was assessed as a function of several independent variables: morphological characteristics; telogen root versus no root; donor age; scalp origin; use of cosmetic hair treatments; and race of the donor. The results show that a positive correlation exists between amplification success and the presence of a telogen root. Combining the amplification success with either the original or optimized protocol, telogen hairs result in an overall success rate of 77.5% compared with 65% for hairs with no roots. Controlling for telogen hairs, the findings indicate that the overall success rate is independent of cosmetic hair treatments; medulla structure; shaft length, diameter, and volume; and scalp origin. Conversely, the age of the donor, the race of the donor, and hair pigmentation all contribute to a variation in amplification success rate.     

Population substructure can significantly affect reliability of a DNA-led process of identification of mass fatality victims

Aiming to evaluate the effects of population substructure on the reliability of a DNA correspondence in the process of human identification, we used the model of "in silico" constructed populations with and without substructure. Effects of population substructure were evaluated at the level of locus heterozygosity, Hardy-Weinberg equilibrium and mini-haplotype distribution. Inbreeding in a subpopulation of 100 individuals through 10 generations did not significantly alter the level of heterozygosity and Hardy-Weinberg equilibrium. However, analysis of mini-haplotype distribution revealed a significant homogenization in separated subpopulations. Average observed mini-haplotype frequency (f(o)) increased to threefold from expected values (f(e)), and the number of mini-haplotypes with f(o)/f(e) above 10 increased over sixfold, suggesting that the effects of population substructure on calculated likelihood ratios (LR) might be larger than previously estimated. In most criminal cases, this would not represent a problem, whereas for identifications in large-scale mass fatality events, population substructure might considerably increase the risk of false identification.