Spotlight

Spotlight

Each month, the Office of Sponsored Programs will spotlight a different PI and their research. If you are interested in being featured in our next spotlight, please email sponsoredprograms@jjay.cuny.edu. Please be sure to provide us with an abstract (3-5 paragraphs) about your research, explanation of your recent project, the amount your project (s) were funded for, special events that you are hosting or coordinating, obstacles or challenges you faced during the application process, if applicable, and a photo of yourself.   

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Dr. Prinz (right) with thesis research graduate students Steven Kranes 
and Stacey Ann Sterling who both graduated in 2017

 

Dr. Mechthild Prinz
Associate Professor, Department of Sciences
John Jay College of  Criminal Justice

Dr. Prinz spent most of her career as a forensic DNA specialist and crime laboratory manager where she played an active role in providing DNA testing results for criminal casework, missing persons and disaster victim identification. 

Every contact leaves a trace, claims the famous maxim attributed to one of the founders of forensic science Edmond Locard in 1930. Back then Mr. Locard did not anticipate modern DNA testing but forensic geneticists have taken this concept to heart ever since Roland van Oorschot in 1997 published on his DNA results for a single fingerprint. Here at John Jay College professor Mechthild Prinz is focusing her research on optimizing biological testing for contact traces. 

The majority of evidence submitted to forensic DNA laboratories consists of biological material left behind through contact, either on worn clothing, e.g. a ski mask in a robbery, or on touched items, e.g. the handle of a baseball bat in an assault. The DNA on these articles stems from a combination of shed skin cells and sweat, and can lead to the perpetrator.  But there are problems: the evidence may not yield enough biological material for a high quality DNA result, and the possibility of passive transfer implies that identifying somebody’s DNA does not necessarily mean this person also touched the item. Dr. Prinz is working on improving the quality of DNA profiles from these contact traces and evaluating passive DNA transfer risks. The most straightforward way of improving DNA results is to boost the amount of DNA recovered from the evidence. One of her projects, funded by PSC-CUNY, is trying to do just that for paper. Handwritten documents like threatening letters or bank robbery notes are important clues, but currently DNA typing is not very successful. 

For other types of evidence, e.g. used cartridge casings, even the best recovery method may not yield typeable DNA and success rates are notoriously low. This is logical, since any biological material on a fired cartridge was exposed to extreme heat and friction. For this evidence type, Dr. Prinz is looking for genetically variant peptides (GVPs) and wants to put protein analysis back into the forensic biology toolbox. ABO blood types, which are based on inherited protein differences, and other blood based proteins used to be the basis for genetic testing in criminal cases and paternity investigations, but these assays were replaced by DNA testing after 1985. So why go back to proteins now?

Each cell has only one set of DNA, but thousands and thousands of protein molecules, making it a sure bet that one can detect proteins even on compromised items with no DNA.  With the advance of proteomics and more powerful technology it is now possible to see genetic variation at the amino acid level, which directly reflects a person’s DNA.  Dr. Glendon Parker introduced the concept of typing GVPs for hair evidence and expanded this to bone samples during his time with the Lawrence Livermore National Laboratory (LLNL) forensic division. Dr. Prinz had the opportunity to obtain funding from LLNL and collaborate with their forensic team on contact traces including fired cartridge casings. 

Her most important finding is that GVP testing can be combined with DNA recovery. Together with students in the MS in Forensic Science program, she developed a new method that separates DNA and proteins from the same fingerprint. They were able to show that the quality of DNA obtained with this new method is equal, if not better than a standard DNA extraction method. The Lawrence Livermore laboratory successfully detected hundreds of peptides that will be evaluated for the presence of GVPs. The method works for fired and unfired cartridge casings made out of different metals. After firing amounts of DNA and protein present on cartridges decreased but with more starting material GVP testing was still possible. The project is continuing with work on the reproducibility of this new assay.

Dr. Prinz was also just notified of a $332,893 award from the National Institute of Justice to determine which factors influence an individual’s propensity to leave DNA behind after contact. This will help assess passive transfer. Her goal is to develop a standardized method to test for shedding propensity. This could theoretically be used to test persons of interest in a case and provide case specific answers. The project also aims at establishing frequencies of high versus low “shedders” in four US ethnic groups. This information will enable scientists to help the court and the juries decide on different active and passive transfer scenarios in a case.