The DNA Unit is divided into three sub-units: Nuclear DNA, Database DNA, and Mitochondrial DNA. DNA, or deoxyribonucleic acid, is the genetic material that makes each person unique. It is found in the nuclei and mitochondria of cells and can be extracted from body fluids or skin cells.
Nuclear DNA sub-Unit
The Nuclear DNA Sub-Unit analyzes DNA from the cell nucleus using STR (short tandem repeats) analysis. This method is highly accurate, works well with degraded samples, and can be automated. Evidence from cases often involves multiple types of samples. Each requires specific DNA tests to provide the most valuable information.
DNA profiles from this unit are entered into CODIS (Combined DNA Index System). CODIS matches profiles to convicted offenders or other cases. Nuclear DNA also uploads eligible profiles to the national database for broader searches.
The DNA Unit reports two types of CODIS matches:
- Offender Hits: Matches between evidence and a convicted offender's profile.
- Forensic Hits: Matches between evidence from different cases, such as missing persons or unidentified remains.
CODIS also includes indices to help identify missing persons or remains.
Database DNA Sub-Unit
The Database DNA Sub-Unit processes DNA from convicted offenders and uploads their profiles into CODIS. CODIS operates on three levels:
- Local Level (LDIS): For city or county labs.
- State Level (SDIS): Matches crime scene profiles with offenders within the state.
- National Level (NDIS): Matches crime scene profiles with offenders across the country.
Mitochondrial DNA Sub-Unit
Mitochondrial DNA (mtDNA) is analyzed when nuclear DNA is unavailable, such as in bones or hair without tissue. The mtDNA is inherited from the mother. It can link an unknown sample to any maternal relative, even across generations. This method is vital for identifying remains in missing person cases. It is also used following mass disasters and when biological material is limited.
Forensic Biology and Hair Analysis
The Forensic Biology Unit examines hair to determine if it is human or animal. For human hair, they check if it was forcibly removed, naturally shed, or treated. If the hair cannot be tested for nuclear DNA, it is sent to the Mitochondrial DNA Sub-Unit for further analysis.
Improvements in Workflow
In 2013, the DNA Unit created a separate lab area for processing "known" samples. These samples include blood or buccal swabs from identified individuals. The separate lab helps speed up processing. It also prevents contamination with evidence samples. Better communication with agencies has led to more elimination samples. This helps refine comparisons and avoid unnecessary CODIS entries.