DNA Evidence & Forensic Biology

Partnering with Law Enforcement and the Criminal and Civil Courts Since 1982

Our forensic biology team has been conducting criminal and civil investigations since 1982 and has been conducting PCR-based DNA evidence analysis over the past 25 years. We have been on the forefront of forensic analysis from a single gene to the state-of-the-art amplification of numerous STRs.

National Acclaim for DNA-based Investigations on Complex Cases

We had the privilege of assisting prosecutors and defense attorneys from across the country with complex evidence such as multiple profiles, mixed evidence, limited biology material to old evidence and more. Our scientists have worked on hundreds of criminal cases, as well as conducting over 100 post-conviction DNA-based investigations that have earned us national acclaim. Our work has also led to the exoneration of over 50 wrongly-convicted defendants including several that had been sentenced to death.

DNA & Forensic Biology Services includes:

    • Evidence Examination for Biological Material
    • State of the Art DNA Typing
    • Evidence Screening / Serology
    • Autosomal STR Analysis Using Investigator® 24plex and Identifiler ®
    • Y-STR Analysis Using Yfiler ®
    • Amylase Diffusion
    • p30 Protein Testing, etc.
    • DNA Profile Interpretation Using STRmix™ Probabilistic Genotyping Software

Our laboratory adheres to a strict in-house quality assurance/quality control program and our DNA section is accredited by ANAB to the current ISO/IEC 17025 international standard and FBI QAS for biological screening and autosomal and Y-chromosome STR analysis in forensic casework. We maintain a trusted relationship with Acadiana Crime Lab that affords us access to search the FBI CODIS database for the genetic profiles we generate.

 

DNA Typing Using Investigator® 24plex, Identifiler®, & Y-Filer®

DNA EvidencePCR-based DNA analysis is very powerful technology for the discrimination of biological evidence sources. It enables scientists to quickly replicate many genes from the small amounts of DNA obtainable from even minute biological deposits and stains. Another advantage of PCR-based DNA typing is the ability to analyze samples that have been compromised by environmental factors or microbial proliferation.

Our laboratory utilizes Investigator® 24plex a Short Tandem Repeat (STR)-based assays for human identification applications. The kit includes a multiplex assay which simultaneously amplifies 22 genetic markers or loci, and a gender-determining marker in human DNA providing discrimination potential to uniqueness. Investigator® 24plex includes the expanded CODIS, the Combined DNA Index System, core loci used by law enforcement to help identify the likely source of biological evidence.

Y-STR analysis at our laboratory through the use of Y-Filer®, a 17 locus assay, meets a specific challenge presented by many forensic samples not otherwise amenable to standard DNA analysis. In mixed samples often encountered in sexual assault cases, where the amount of female DNA can overwhelm or mask low-level male DNA, Y-STR analysis targets only genes on the Y chromosome, thereby effectively isolating the male DNA. In this fashion, a variety of samples that have been problematic in the past are now capable of genetic discrimination.

Examples where this technology is useful include female body/skin swabs with low numbers of male epithelial cells, fingernail scrapings or clippings from female victims, items handled or worn by male assailants during the commission of a crime, and in determining the number of males contributing to complex mixtures. While not as discriminating as standard autosomal DNA testing, the ability to detect only DNA deposited by a male expands the range of samples on which successful DNA analysis can be performed, providing another powerful investigative tool to potentially link the perpetrator to a crime.

Evidence Examination for Biological Material

DNA EvidenceOur Forensic Biology team is comprised of experienced scientists who understand the broad aspects of forensic science as well as the details of DNA analysis. Our scientists will articulate the how, what, where, and why of biological evidence, providing the best way to locate biological deposits, determine how to obtain the best data from challenging samples and how to clearly present findings in court. Our services involve examining evidence items for body fluid deposits such as blood, semen, and saliva as well as dealing with other potential physical evidence such as hair, fiber, bloodstain patterns, gunshot residue and other materials encountered during the investigation.

Probabilistic Genotyping

Traditional interpretation of DNA typing results from evidence is performed using so-called binary methods. These methods are prone to subjective interpretation of results by analysts. Probabilistic genotyping using continuous models makes use of the allele peak data from an electropherogram for a more powerful interpretation. We employ STRmix™  probabilistic genotyping software to aid in the interpretation of DNA typing results from evidence comprised of up to four contributors. STRmix™  uses an MCMC-based fully-continuous analysis to determine the probable genotypes of the contributors to a DNA result.