Biology Section
The Washoe County Sheriff’s Office (WCSO) Biology section consists of 3 units: Screening and Sample Preparation Unit, Casework DNA Analysis Unit, and DNA Databasing Unit.
Evidence Submission and Testing Policy
Sample Submission:
- Evidence must be dried and packaged in paper, not plastic, to prevent DNA degradation.
Prioritization:
- Cases are typically queued for testing based on the case type and submission approval date (after all items have been submitted to the lab), but can be adjusted on a case-by-case basis. The prioritization of cases is managed by the Biology Supervisors.
- Cases are prioritized based on community threat, court dates, and crime severity (homicides & sexual assaults are typically prioritized over all other case types).
Tiered Testing Approach:
Tier I: Immediate threat to the community (limited sample testing).
Tier II: Standard Analysis:
- Homicides: Up to 15 evidentiary samples and appropriate reference samples.
- Sexual Assault: All sexual assault kits (except non-investigatory kits), along with other relevant items such as underwear, condoms, etc., and appropriate reference samples. The sexual assault kit will be tested prior to any additional items, unless the synopsis indicates the need for the additional item to be tested simultaneously (e.g. condom was used and submitted).
- Crimes Against a Person: Up to 4 evidentiary samples and appropriate reference samples.
- Property Crimes: Up to 2 evidentiary samples and appropriate reference samples.
Tier III: Additional Testing based on investigative or court needs.
Cases not typically analyzed for DNA: Weapons violations, controlled substances, possession of stolen property, larceny, and vandalism cases.
Screening and Sample Preparation Unit:
- This unit selects and prepares samples for nuclear DNA analysis.
- A brief case synopsis addressing how items submitted for testing are associated with the crime is extremely helpful in ensuring the appropriate testing is conducted.
- Evidence may be screened for the presence of biological fluid stains such as blood, semen, and saliva. Stains may be visible or require special lighting.
- Biological fluid tests are used to determine if a stain could be blood, semen, or saliva. These tests may be presumptive (not 100% specific) or confirmatory (specific).
- Evidence that does not contain biological stains but may have DNA present due to handling/touching are also prepared for DNA analysis.
- Reference samples (swabs of the inside of a person’s cheek) from appropriate individuals (suspect, victim, etc.) should always be submitted when possible.
- Hairs with suitable DNA roots can be collected for analysis.
- Fluids like feces, urine, vomit, and tissue preserved in formaldehyde are not accepted.
Biological fluid tests:
- Tests used: Kastle-Meyer (blood), ABAcard HemaTrace (human blood), Acid Phosphatase (seminal fluid), ABAcard p30 (seminal fluid), RSID-Saliva (saliva), and Microscopic Examinations (spermatozoa).
Sexual Assault Victim and Suspect Kits:
- Free kits for collecting evidence from sexual assault victims and suspects are available to SART facilities.
Casework DNA Analysis Unit:
- Evidentiary samples and reference samples are extracted, quantified, and subjected to Short Tandem Repeat (STR) analysis or Y STR analysis to generate DNA profiles.
- STRs are regions of DNA where a short sequence of DNA is repeated multiple times in a row. The number of these repeats varies between individuals and is therefore the basis of DNA profiling.
- Y STR is used to analyze STRs on the Y Chromosome found in biological males and passed down the paternal lineage. This type of testing is frequently used in sexual assault cases.
- STR/Y STR DNA profiles from evidentiary samples are compared to reference sample profiles.
- Suspect profiles from crime scene evidence may be eligible for entry into the DNA database called Combined DNA Index System (CODIS) for searching purposes.
- The WCSO FSD does not perform mitochondrial DNA testing.
DNA Kits Used:
- Quantifilier™ Trio Kit: Quantifies the amount of DNA present in a samples.
- GlobalFiler™ Kit: STR Analysis (human DNA)
- YFiler™ Plus Kit: Y STR Analysis (male DNA)
Conclusions/Statistics:
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A match between DNA profiles from the evidence and a reference sample, results in report phrases like "cannot be excluded" or "support for inclusion" with statistical weight for the match.
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If an evidentiary DNA profile does not match the reference DNA profile, an exclusion phrase will be reported.
CODIS (Combined DNA Indexing System)
- A computerized database of DNA profiles from suspect profiles from crime scenes, convicted offenders, felony arrestees, missing person profiles, unidentified human remains, and relatives of missing persons.
- Used to link cases and identify suspects by comparing profiles in the database.
- Database searching may occur at both the State and National level depending on the quality of the DNA profile.
- Nevada Law: Felony offenders, certain misdemeanants, and felony arrestees must submit DNA for inclusion.
- Exclusion of Victim DNA: Victim DNA must be excluded before entering unknown profiles into CODIS.
- Specific information regarding the evidence submitted, such as a case synopsis, is typically required to determine CODIS eligibility.
For more information on CODIS, visit the FBI's website.
DNA Databasing Unit:
The State of Nevada requires anyone convicted of a felony or certain misdemeanors and anyone arrested for a felony to provide a DNA sample for inclusion into the DNA offender database. Refer to NRS 176.0911, NRS 176.0913, and NRS 176.09123.
The DNA Databasing Unit processes these samples for upload into CODIS.