Module 4 Sample Handling and Evidence

What is chain of custody?

Establishing a paper trail with items of physical evidence.

What does chain of custody help demonstrate?

Integrity of the connection between the items collected and the data analyzed.

What is the purpose of maintaining chain of custody in forensic laboratories?

To ensure proper sample collection, transfer, and analysis.

Why is chain of custody important in court?

It helps present the integrity of evidence.

What is contamination?

The unintentional introduction of exogenous DNA into a DNA sample or PCR reaction.

Why is contamination such a critical issue with PCR?

Contamination is a critical issue with PCR because it can lead to non-specific amplification and false positives.

What are the three types of contamination?

analyst to sample, sample to sample, and environment to sample.

How can you minimize contamination risk?

Not touching it with your bare hands, don't sneeze or cough over the evidence; use clean latex gloves.

What is a positive control?

A known sample taken through an analytical process to verify that the various steps are working properly.

What is a negative control?

A sample consisting of only PCR amplification reagents without the addition of template DNA; presence of DNA indicates contamination.

How is the DNA laboratory set up?

Separate work areas (pre and post PCR activities). Workflow from least contamination room to most contamination. Using different fume hoods for different steps of the DNA process such as a fume hood for quantitation is not to be used for amplification.

What is the swipe test?

A reliable method for determining contamination without the use of special equipment, performed if contamination is determined to be systemic.

FBI Quality Assurance Standards for DNA Testing Laboratories

A set of standards that laboratories must follow to maintain a documented quality system appropriate to testing activities.

Internal audit

An evaluation of the entire operation of a laboratory conducted every year by laboratory management or an independent organization.

When do we conduct an external audit?

An evaluation of the laboratory conducted every two years by an independent organization according to pre-established guidelines.

What is the ISO audit?

An audit that occurs every four years to evaluate the laboratory's compliance with international standards.

When is the ISO audit done?

ISO is done every four years.

What is the purpose of an analyst taking biannual proficiency test?

The purpose of the test is to evaluate the analyst's ability to obtain a consistent result using the laboratory's approved SOPs.

What are critical reagents?

Critical reagents are those whose performance is vital to the success of the DNA testing and require testing on known samples before use on forensic or casework reference samples.

What are the critical kits that we use in the lab?

GlobalFiler Amplification Kit, YFiler Plus Amplification Kit, and Quantifiler Trio DNA Quantitation Kit.

When we test new lot number kits, what are the reagents used?

When a new lot number of kits are received, it will be tested using the positive control included with the kit, negative amplification control, and an additional known in-house DNA sample.

What is the purpose of validation studies?

The purpose of validation studies is to ensure that procedures performed in the laboratory accurately reflect the examined samples.

When does an Internal Validation occur?

Internal validation is performed by an individual lab when a new method is introduced.

What does external validation means?

External validation is when a DNA laboratory may rely upon a company's developmental validation studies.