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Forensic Science

Forensic Biology (Serology and DNA)

Photo of stains

Locating Body Fluid Stains

Photo of DNA Type

Processing Stains for DNA Typing

The Forensic Biology Unit is tasked with examining physical evidence to locate, identify, and perform DNA testing on a range of biological material. The unit conducts analysis on crimes such as homicide and sex crime cases, but also performs testing on robberies, assaults, and a variety of property crimes.

The testing process after identifying the suspected biological material consists of DNA extraction/purification, estimating the amount of human DNA in the samples, and conducting PCR (polymerase chain reaction) based amplification of the samples to generate the DNA profiles from the items that will be used for comparison purposes.

Comparisons are made to individuals thought to be associated with the crime in question (victims, suspects, or witnesses) or alternatively the Combined DNA Index Systems (CODIS) databases can be queried for potential investigative leads.  Currently in the State of California there are approximately 2 million individuals and several thousand casework samples available for comparison in the database.

An additional function the Unit performs which deals with blood, but is not strictly a Forensic Biology function, is bloodstain pattern interpretation. This sub-discipline of the forensic sciences is useful primarily in the field, and occasionally in the laboratory, where the careful examination of bloodstain patterns includes the determination of the point of origin of the bloodstains, and information as to the mechanism that caused the blood droplets to be produced, which is information that can be useful to the reconstruction of the crime.