DNA (Deoxyribonucleic Acid)

SWGDAM recently issued recommendations on genotyping results reported as likelihood ratios, designed to promote consistency among laboratories. Members of the committee will discuss the recommendations and their foundations.

This webinar was presented by the NIJ Forensic Technology Center of Excellence on October 18, 22018.

This webinar will provide an evaluation of the DEPArray™, a system that enables the identification, separation, and recovery of single cells or groups of cells from heterogeneous mixtures. The workflow described in this webinar will highlight the impact this instrument, with standard forensic processes, will have on processing sexual assault evidence and improving the success of single cell analyses.

Many working with genomic DNA can afford to lose large portions of it during its extraction without negatively impacting downstream analysis.  However, with work targeting highly degraded DNA sources, retention of every molecule can be key to successful analyses.   This webinar addressed the insufficient documentation of absolute efficiencies of extraction methods and the nature of DNA loss associated with the study of low copy number and degraded DNA samples.

This webinar focused on the use of PACE™, a method developed by Syracuse University, to perform artifact management and probabilistically predict the number of contributors (NOC) in forensic DNA samples. This is performed using a combination of biological modeling and machine learning, permitting high accuracy NOC calls (greater than 90%) of complex mixtures. It does so rapidly (seconds to minutes) without the need for high performance computing resources.

This webinar highlighted the results of a full developmental validation of a method that estimates the A Posteriori Probability (APP) of the number of contributors in a DNA sample(NOC), and demonstrated that estimating the APP based on peak heights outperforms methods that rely on binary determinations alone. This presentation focused on including the true NOC in Likelihood Ratio interpretations and on repeatability.

This webinar was presented by the NIJ Forensic Technology Center of Excellence on July 14, 2020.

Improving the overall response to sexual assault includes understanding how touch DNA evidence impacts groping sexual assault cases. This webinar will illustrate the importance of these cases and highlight proposed guidelines for evidence collection.

This webinar was presented by the NIJ Forensic Technology Center of Excellence on February 27, 2019.

This webinar built on the concepts presented in the webinar “The Time to Collect is Now: DNA Evidence in Groping Sexual Assault Cases” presented by Dr. Julie Valentine.

In this webinar we discussed the theory and development of Investigative Genetic Genealogy, including some ethical and legal considerations raised by this technique.  Additionally, we explored the current status of case investigations, the impact on crime laboratories, implementation strategies, and recommendations for jurisdictions considering applying Investigative Genetic Genealogy to their unsolved cases.

This webinar was presented by the NIJ Forensic Technology Center of Excellence on January 23, 2020. 

Microhaplotypes (microhaps) are biomarkers fewer than 300 nucleotides long that display multiple allelic combinations. The main advantages of microhaps over conventional short tandem repeats (STRs) include the 1) absence of stutter, 2) same-size alleles within each locus, 3) lower mutation rate, and 4) ancestry informative alleles. These forensically relevant loci can yield a power of discrimination similar to STRs while enhancing human identification (HID), mixture deconvolution, and biogeographic ancestry prediction.

Touch DNA is a potentially powerful sample type for forensic casework, but is challenging to work with due to low quantity, variable deposition amounts, and fundamental questions regarding stability over time. In this webinar we describe best-practices and initial results related to comprehensive studies of the stability of touch DNA after exposure to different environmental conditions.

This webinar was presented by the NIJ Forensic Technology Center of Excellence on March 11, 2021.

Throughout the Probabilistic Genotyping of Evidentiary DNA Typing Results virtual workshop series, we have reviewed aspects of DNA mixture interpretation and have seen that probabilistic genotyping (PG) software can serve as a tool to assist the DNA Examiner in identifying possible genotype sets within a mixture and then calculating a likelihood ratio (LR). Approaches to modeling were shared by the developers of different PG software programs, followed by examples of internal validation studies and results.

Has a person of interest contributed DNA to a mixture obtained from evidence? Is that DNA associated with a crime? Both are questions that cannot be answered with absolute certainty. This module of the Probabilistic Genotyping of Evidentiary DNA Typing Results workshop series addresses the uncertainty and limitations of probabilistic genotyping systems that are used to calculate likelihood ratios and infer genotype sets from DNA typing results.

Biological modeling, statistical theory, and the computer processing of probabilistic genotyping systems are based on long- standing principles, yet their usage in U.S. courts has been limited to the past few years. This module of the Probabilistic Genotyping of Evidentiary DNA Typing Results web series addresses topics relevant to the admissibility of probabilistic genotyping results and the presentation of results in criminal proceedings. Various decisions related to probabilistic genotyping will be summarized from a legal perspective.

Historically, the predominant means of assigning statistical weight to many DNA mixtures in the U.S. has been the combined probability of inclusion, or CPI. Accordingly, many forensic DNA analysts, as well as attorneys and judges, are well-versed in the CPI as a match probability. In the fifth module of this workshop series devoted to probabilistic genotyping, the presenters will help DNA analysts and legal professionals understand degrees of statistical weight and properly communicate likelihood ratios and their meaning.