Abstract: The technology for producing DNA profiles is very sensitive and is able to produce profiles from process negative controls typically consisting of one or two peaks, a phenomenon known as dropin. There are several types of models that implement likelihood ratios for the statistical evaluation of DNA profiles. One of the types is the family of continuous models because they consider continuous peak height/area measurements from the stain profile. Nowadays, there are several continuous models available. The aim of this article is to expose a statistical model for dropin peak heights supported by data, and illustrate its incorporation into a continuous method.
Abstract: In recent years, the use of DNA data for personal identification has become a crucial feature for forensic applications such as Disaster Victim Identification (DVI). Computational methods to cope with these kinds of problems must be designed to handle large scale events with a high number of victims, obtaining likelihood ratios and posterior odds with respect to different identification hypotheses. Trying to minimize identification error rates (i.e. false negatives and false positives), a number of computational methods, based either on the choice between alternative mutation models or on the adoption of a different strategy, are proposed and evaluated. Using simulation of DNA profiles, our goal is to suggest which is the most appropriate way to address likelihood ratio computation in DVI cases, especially to be able to efficiently deal with complicating issues such as mutations or null alleles, considering that data about these latter are limited and fragmentary.
Abstract: Emerging next-generation sequencing technologies will enable DNA analyses to add pigmentation predictive and ancestry informative (AIM) SNPs to the range of markers detectable from a single PCR test. This prompted us to re-appraise current forensic and genomics AIM-SNPs and from the best sets, to identify the most divergent markers for a five population group differentiation of Africans, Europeans, East Asians, Native Americans and Oceanians by using our own online genome variation browsers. We prioritized careful balancing of population differentiation across the five group comparisons in order to minimize bias when estimating co-ancestry proportions in individuals with admixed ancestries. The differentiation of European from Middle East or South Asian ancestries was not chosen as a characteristic in order to concentrate on introducing Oceanian differentiation for the first time in a forensic AIM set. We describe a complete set of 128 AIM-SNPs that have near identical population-specific divergence across five continentally defined population groups. The full set can be systematically reduced in size, while preserving the most informative markers and the balance of population-specific divergence in at least four groups. We describe subsets of 88, 55, 28, 20 and 12 AIMs, enabling both new and existing SNP genotyping technologies to exploit the best markers identified for forensic ancestry analysis.
Abstract: To assess the level of mtDNA sequence heteroplasmy in dog hair, we sequenced a 612 base pair fragment of the hypervariable region 1 (HVI) in 576 hairs from six dogs representing a range of age, sex, breed, and hair color. Blood and buccal samples were collected from each dog for reference. Three instances of sequence heteroplasmy were observed at nucleotide positions 15627 (G/A), 15628 (T/C) and 15639 (G/A) in two hairs from different dogs. An HVI sequence heteroplasmy frequency of 0.0034 was obtained. The Probability of Identity (PI) value, or probability that two random, unrelated dog hairs share an HVI sequence, and the Power of Discrimination (PD), or probability that two random unrelated dog hairs have different HVI sequences, were determined from the 88 HVI haplotypes represented in the Veterinary Genetics Laboratory database (n=1006) and found to be 0.086 and 0.914, respectively.
Abstract: Recently, many researchers have focused on analysis of different X-chromosomal STRs as they bear the potential to efficiently complement the analysis of autosomal and Y-chromosomal STRs in solving special complex kinship deficiency cases. In the current study we examined a sample of 250 unrelated Egyptian males with the Investigator Argus X-12 kit (Qiagen GmbH, Hilden, Germany) which detects 12 X-STR markers distributed over the entire X-chromosome as four closely linked clusters. Microvariant off ladder alleles as well as null alleles have been detected in some loci. Furthermore, discordant results were observed between the Investigator Argus X-12 and the Mentype® Argus X-8 kits (Biotype AG, Dresden, Germany). New primers were designed for loci DXS10101, DXS10146 and DXS10148 to correct the allele drop outs observed in these loci with the Investigator Argus X-12 kit. Additionally, DNA sequence analysis revealed the polymorphisms responsible for the allele drop outs. Furthermore, six additional X-STRs (DXS10161, DXS10159, DXS10162, DXS10163, DXS10164 and DXS10165) located in the centromere region at Xp11.21-Xq11.1 were examined in a single multiplex reaction. Allele and haplotype frequencies as well as different forensic statistical parameters of the 18 X-STR loci tested indicated that they are highly informative in different forensic applications in the Egyptian population. However, some modifications still need to be performed on the Investigator Argus X-12 kit before its use in forensic casework is validated.
Abstract: Walsh et al. outlined a method for adjusting autosomal coancestry values, ?A, to take account of the existence of a Y chromosome match, ?A|Y. The framework established by Walsh et al. is flexible and allows an investigation of some real world effects such as family structure. It also allows the effect of a Y chromosome match to be placed within the construct of existing casework practice. Most notable is the ability to deal with an assigned value for the autosomal coancestry coefficient and the fact that most casework statistics report a value for unrelated individuals unless case circumstances suggest differently. The values of ?A|Y are not much larger than ?A and a coherent argument could be made that any adjustment is unnecessary.
Abstract: DNA-STR analysis is widely used in the forensic science field and has important requirements on the analysis time to obtain faster inspections. The developed forensic STR Kit, referred to as Expressmarker 16 (EX16), could shorten the amplification time to a minimum of 35min. It enables 16 STR loci to be co-detected, including 13 CODIS loci, D2S1338, D6S1043 and Amelogenin loci. The kit is validated by a series of tests formed by DNA mixtures, stutter ratios, optimized PCR protocols based on annealing temperature research, species specificities, inhibitors, sensitivity, and parallel tests according to FBI QAS (2009/2011). The results demonstrated that EX16 was a useful tool for rapid criminal investigation.
Forensic scientists can now more quickly assess the quantity and quality of human DNA in highly compromised and degraded casework samples and provide the critical information needed to drive informed decisions on subsequent steps in the analysis process, thanks to two new Life Technologies quantification solutions announced today by Thermo Fisher Scientific.
Abstract: Current assessment of whether a forensic evidence item should be submitted for STR profiling is largely based on the personal experience of the Crime Scene Investigator (CSI) and the submissions policy of the law enforcement authority involved. While there are chemical tests that can infer the presence of DNA through the detection of biological stains, the process remains mostly subjective and leads to many samples being submitted that give no profile or not being submitted although DNA is present. The ParaDNA® Screening System was developed to address this issue. It consists of a sampling device, pre-loaded reaction plates and detection instrument. The test uses direct PCR with fluorescent HyBeacon™ detection of PCR amplicons to identify the presence and relative amount of DNA on an evidence item and also provides a gender identification result in approximately 75minutes. This simple-to-use design allows objective data to be acquired by both DNA Analyst and non-specialist personnel, to enable a more informed submission decision to be made. The developmental validation study described here tested the sensitivity, reproducibility, accuracy, inhibitor tolerance, and performance of the ParaDNA Screening System on a range of mock evidence items. The data collected demonstrates that the ParaDNA Screening System identifies the presence of DNA on a variety of evidence items including blood, saliva and touch DNA items.