FDC Forensic Laboratory Procedures 4

Question 1

A forensic laboratory uses Chelex-100 extraction. What is the primary advantage of this method over organic extraction?

Accepted Answer

It is faster and simpler with fewer toxic reagents

Answer

Chelex-100 extraction is faster, involves fewer steps, and does not require hazardous organic solvents like phenol-chloroform.

Question 2

In forensic DNA analysis, what does the term 'stochastic effects' refer to?

Accepted Answer

Random variation in peak heights resulting from low template DNA amounts

Answer

Stochastic effects arise when low template DNA is amplified, causing random allele dropout, drop-in, or extreme peak height imbalance.

Question 3

Which of the following is a correct statement about laboratory accreditation under ISO/IEC 17025?

Accepted Answer

Accreditation confirms that the laboratory's management system and technical competence meet international standards

Answer

ISO/IEC 17025 accreditation assesses both the management system and technical competence of the testing laboratory, not individual analysts.

Question 4

What is the purpose of a negative PCR control in a forensic STR amplification batch?

Accepted Answer

To confirm that no contaminating DNA was introduced during PCR setup

Answer

A negative PCR control contains all amplification reagents but no DNA template; any profile it yields indicates contamination during PCR setup.

Question 5

A forensic analyst observes a 'minus A' artifact on an electropherogram. What causes this?

Accepted Answer

Polymerase failing to add the non-templated adenylate nucleotide to PCR products

Answer

Taq polymerase typically adds a non-templated adenosine to PCR products; incomplete adenylation (-A) produces a peak one base pair smaller than the fully adenylated product.

(FDC) Forensic DNA Certification Practice Test

(FDC) Forensic DNA Certification Practice Test

FDC Forensic Laboratory Procedures 4