Question 1

Which of the following best explains why 'anonymous' DNA sequences are used for forensic DNA profiling rather than sequences that code for proteins?

Accepted Answer

Anonymous sequences are not linked to any known traits, preserving individual privacy.

Question 2

A forensic scientist is analyzing a degraded DNA sample from a crime scene. Which DNA profiling method is most appropriate and why?

Accepted Answer

STR analysis, because STR loci are short and can be amplified even from partially degraded DNA.

Question 3

During PCR, which step is responsible for the specificity of the DNA region that is amplified?

Accepted Answer

Annealing of primers at $$45-65\ ^\circ\mathrm{C}$$

Question 4

A suspect’s genotype at the TH01 STR locus is 6-8. What does this mean?

Accepted Answer

The suspect has 6 and 8 copies of the [TCAT] repeat on each homologous chromosome.

Question 5

Which of the following is a key reason why Taq DNA polymerase is used in PCR?

Accepted Answer

It is resistant to high temperatures required for DNA denaturation.

Question 6

A crime scene sample contains only a few cells. Which combination of techniques would best allow you to generate a DNA profile?

Accepted Answer

Extract DNA, perform PCR amplification of STR loci, analyze by agarose gel electrophoresis.

Question 7

Which of the following best describes the inheritance pattern of VNTR and STR loci?

Accepted Answer

Autosomal codominant

Question 8

Why is it important to analyze multiple STR or VNTR loci when creating a DNA fingerprint?

Accepted Answer

To decrease the probability of a coincidental match between unrelated individuals.

Question 9

A PCR reaction is set up with the following cycling conditions: initial denaturation at $$94\ ^\circ\mathrm{C}$$ for 2 min, then 35 cycles of $$94\ ^\circ\mathrm{C}$$ for 30 sec, $$52\ ^\circ\mathrm{C}$$ for 30 sec, $$72\ ^\circ\mathrm{C}$$ for 30 sec, and a final extension at $$72\ ^\circ\mathrm{C}$$ for 10 min. What is the purpose of the final extension step?

Accepted Answer

To allow Taq polymerase to complete synthesis of all DNA strands.

Question 10

In the context of the COVID-19 pandemic, which molecular biology technique is used to detect the presence of SARS-CoV-2 RNA in patient samples?

Accepted Answer

Reverse transcription followed by PCR (RT-PCR)

Question 11

A student accidentally transfers chelex beads into the PCR reaction during DNA extraction from cheek cells. What is the most likely outcome?

Accepted Answer

The PCR will fail because chelex beads chelate Mg$$^{2+}$$, which is required by Taq polymerase.

Question 12

Which of the following best explains why DNA samples are loaded near the negative (black) electrode during agarose gel electrophoresis?

Accepted Answer

DNA is negatively charged and migrates toward the positive electrode.

Question 13

A forensic lab is comparing DNA from a crime scene to four suspects using RFLP analysis. Which of the following steps is NOT required for this analysis?

Accepted Answer

Amplifying DNA with PCR before digestion.

Question 14

Which of the following statements about STRs and VNTRs is correct?

Accepted Answer

VNTRs are longer repeat units (10-100 bp) while STRs are shorter (2-9 bp).

Question 15

A DNA sample is digested with EcoRI and PstI and analyzed by agarose gel electrophoresis. The resulting pattern matches that of suspect 3. What does this indicate?

Accepted Answer

Suspect 3's DNA matches the DNA found at the crime scene.

Question 16

Which of the following best describes the role of primers in PCR?

Accepted Answer

They provide a starting point for DNA synthesis by binding to specific sequences flanking the target region.

Question 17

If a person is heterozygous at the D1S80 VNTR locus, what would you expect to see after PCR amplification and agarose gel electrophoresis?

Accepted Answer

Two bands of different sizes, each corresponding to a different allele.

Question 18

Which of the following is a critical reason for including DNA from all investigators in the analysis of crime scene samples?

Accepted Answer

To exclude the possibility that DNA from investigators contaminated the crime scene samples.

Question 19

A PCR master mix contains all of the following EXCEPT:

Accepted Answer

Template DNA

Question 20

Which of the following best explains why RFLP analysis is rarely used in modern forensic investigations?

Accepted Answer

It requires large amounts of high-quality DNA, which is often not available from crime scenes.

DNA Profiling Techniques in Forensic Biochemistry: RFLP, STR, and VNTR Analysis

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