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Forensic Biology & DNA

Scientists with the Forensic Biology Section examine evidence for the presence of body fluids such as blood, semen, and saliva and conduct DNA analysis on evidence containing these body fluids.  DNA profiles generated from evidence can then be compared to DNA samples from victims and other subjects involved in a case.  The Forensic Biology Section analyzes evidence from a wide range of cases, including property crimes as well violent crimes such as sexual assaults, homicides, and robberies.

Serology and DNA Analysis
Most cases go through serology testing prior to DNA analysis.  A serologist identifies areas on evidence that may contain a body fluid that can be tested for DNA. 

Next, DNA analysts follow a standard process to analyze items that may contain even very small amounts of DNA.  A technique called the Polymerase Chain Reaction (PCR) allows an analyst to target specific areas on the DNA identified for forensic testing and make millions of copies of these areas.  DNA profiles can then be generated and visualized using a technique that separates the DNA fragments based on their size.
Cases without a suspect
DNA evidence can be especially helpful in cases without a known suspect.  DNA profiles generated from evidence can be used to search the state’s database of convicted offender and arrestee DNA samples.
Here’s how the process works in cases where law enforcement does not have a suspect:

  • Crime Lab scientists analyze evidence and develop a DNA profile of a possible suspect.  
  • That DNA profile is used to search the DNA database, known as the Combined DNA Index System (CODIS). 
  • If the DNA sample searched against CODIS matches a DNA sample already in the database, that is known as a "hit." 
  • A hit can pinpoint a potential suspect, or link a case in North Carolina to other cases from around the country.
  • When a hit identifies a potential suspect, this gives law enforcement probable cause to collect a known DNA sample from the potential suspect.
  • Crime Lab scientists use the known DNA sample to confirm the hit.

Forensic Biology & DNA Section:  Forensic Scientist Manager Jody H. West