Robin W. Cotton

Isolation of Deoxyribonucleic Acid (DNA) from Saliva and Forensic Science Samples Containing Saliva

Saliva and saliva-stained materials were examined as potential sources of deoxyribonucleic acid (DNA) for DNA analysis and identity testing. In this paper, the authors demonstrate that DNA was isolated and DNA banding patterns suitable for DNA typing were obtained from fresh saliva and various saliva-stained materials, such as envelopes, buccal swabs, gags, and cigarettes. Furthermore, DNA and DNA banding patterns were obtained from actual forensic evidentiary samples containing mixed saliva/semen stains. The DNA banding patterns obtained from saliva or saliva-stained material were indistinguishable from the patterns obtained from blood or hair from the same individual. Intact DNA was readily isolated and DNA banding patterns were obtained from saliva stored at -20 degrees C and dried saliva stains stored under varying conditions. We conclude that saliva and saliva-stained material can be good sources of DNA for analysis and for DNA typing in certain forensic settings.

Analytical Thresholds and Sensitivity: Establishing RFU Thresholds for Forensic DNA Analysis,†‡

Determining appropriate analytical thresholds (ATs) for forensic DNA analysis is critical to maximize allele detection. In this study, six methods to determine ATs for forensic DNA purposes were examined and compared. Four of the methods rely on analysis of the baseline noise of a number of negatives, while two utilize the relationship between relative fluorescence unit signal and DNA input in the polymerase chain reaction (PCR) derived from a dilution series ranging from 1 to 0.06 ng. Results showed that when a substantial mass of DNA (i.e., >1 ng) was amplified, the baseline noise increased, suggesting the application of an AT derived from negatives should only be applied to samples with low levels of DNA. Further, the number and intensity of these noise peaks increased with increasing injection times, indicating that to maximize the ability to detect alleles, ATs should be validated for each post‐PCR procedure employed.

Investigation of Reproducibility and Error Associated with qPCR Methods using Quantifiler® Duo DNA Quantification Kit

Abstract:  Reproducibility of quantitative PCR results is dependent on the generation of consistent calibration curves via accurate volume transfers and instrument performance. A review of 14 standard curves, using two different QuantDuo® standard DNA lots, showed variability of cycle threshold values between assays were larger than those of the Internal PCR Control (IPC). This prompted a set of experiments designed to determine the source of variability. Results showed that error introduced during DNA addition to the plate resulted in little variation. A comparison of seven independent series demonstrated cycle threshold variation between dilutions was larger than the variation expected from repeated samples. Modeling the influence of pipette errors on dilution series accuracy indicated that a more rigorous approach to external calibration curve production is required and showed that improvement in calibration curve stability is expected if the pipette conditions are carefully chosen and/or a single validated curve is utilized as the calibrator.

Review: Properties of sperm and seminal fluid, informed by research on reproduction and contraception

Forensic DNA testing is grounded in molecular biology and population genetics. The technologies that were the basis of restriction length polymorphism testing (RFLP) have given way to PCR based technologies. While PCR has been the pillar of short tandem repeat (STR) methods and will continue to be used as DNA sequencing and analysis of single nucleotide polymorphisms (SNPs) are introduced into human identification, the molecular biology techniques in use today represent significant advances since the introduction of STR testing. Large forensic laboratories with dedicated research teams and forensic laboratories which are part of academic institutions have the resources to keep track of advances which can then be considered for further research or incorporated into current testing methods. However, many laboratories have limited ability to keep up with research advances outside of the immediate area of forensic science and may not have access to a large university library systems. This review focuses on filling this gap with respect to areas of research that intersect with selected methods used in forensic biology. The review summarizes information collected from several areas of the scientific literature where advances in molecular biology have produced information relevant to DNA analysis of sexual assault evidence and methods used in presumptive and confirmatory identification of semen. Older information from the literature is also included where this information may not be commonly known and is relevant to current methods. The topics selected highlight (1) information from applications of proteomics to sperm biology and human reproduction, (2) seminal fluid proteins and prostate cancer diagnostics, (3) developmental biology of sperm from the fertility literature and (4) areas where methods are common to forensic analysis and research in contraceptive use and monitoring. Information and progress made in these areas coincide with the research interests of forensic biology and cross-talk between these disciplines may benefit both.

The effects of differential extraction conditions on the premature lysis of spermatozoa.

The purpose of this study was to determine the effect Proteinase K, sodium dodecyl sulfate (SDS), incubation times, and temperatures had on differential extraction efficiencies and the premature lysis of spermatozoa. The effect was measured using Quantifiler® Duo and Identifiler™ PCR Amplification kits, where the resultant male and female DNA concentrations and their ratios within the nonsperm‐ and sperm fractions (SFs) were determined. Comparisons between expected and observed ratios illustrate the quantity of female DNA in the SF increased when Proteinase K was absent during the initial incubation. Additionally, there is no indication of simultaneous sperm and epithelial cell lysis in the absence of DTT at Proteinase K concentrations ranging from 10 to 300 μg/mL. All other conditions exhibited minimal variation in DNA concentration. Therefore, despite the various protocols used for the differential lysis of cell mixtures encountered in casework, the method is robust and successful at most conditions.

Use of Deoxyribonucleic Acid (DNA) Fingerprints for Identity Determination: Comparison with Traditional Paternity Testing Methods—Part II

Six red blood cell (RBC) antigen systems, coupled with human lymphocyte antigen (HLA) phenotyping, were used to establish paternity on 28 mother/child/alleged-father trios. Samples were subsequently examined using the deoxyribonucleic acid (DNA) fingerprinting test with the multilocus Jeffreys DNA probes 33.6 and 33.15. In 27 of 28 paternity cases, the DNA fingerprinting test results supported and enhanced the results of RBC and HLA typing by resolving disputed paternity cases conclusively. One discrepancy between conventional serological methods and DNA analysis is discussed.

Determination of the possible number of genotypes which can contribute to DNA mixtures: Non-computer assisted deconvolution should not be attempted for greater than two person mixtures

When DNA profiles contain a mixture of contributors (N), the maximum number of alleles observed at any locus is 2 N with the number of alleles varying between 1 and 2 N. The number of possible combinations of the genotypes of the N contributors increases as N increases. The number of possible combinations of genotypes that may occur among the N contributors can be enumerated using the mathematical concept of ordered partitions. Thus the number of possible genotype combinations which can exist at an STR locus in a DNA sample having N contributors and L observed alleles at the locus can be calculated. Development of the calculation and the resulting number of possible combinations which exist for N ≤ 8 contributors is presented. The results for ≥ three contributors indicate that deconvolution of contributing genotypes using manual methods is precluded except in circumstances where a clear major contributor can identified.