Question 1

Which step in the PCR process is responsible for separating the two strands of DNA, and what temperature is typically used for this step?

Accepted Answer

Denaturation; 95°C

Question 2

What is the primary function of primers in PCR?

Accepted Answer

To bracket the region of DNA to be amplified and provide a starting point for DNA polymerase

Question 3

Why is Taq polymerase used in PCR instead of eukaryotic DNA polymerases?

Accepted Answer

Taq polymerase is not denatured by the high temperatures used in the denaturation step

Question 4

If a PCR reaction starts with 1 double-stranded DNA molecule, how many double-stranded DNA molecules will be present after 3 cycles, assuming perfect efficiency?

Accepted Answer

$$2^3 = 8$ (but the correct answer is 16)

Question 5

Which of the following is NOT a required reagent for a standard PCR reaction?

Accepted Answer

Reverse transcriptase

Question 6

In a COVID-19 diagnostic PCR test, what is the purpose of reverse transcription?

Accepted Answer

To convert viral RNA into complementary DNA (cDNA) for PCR amplification

Question 7

What is the role of gel electrophoresis following PCR amplification?

Accepted Answer

To separate DNA fragments based on their size

Question 8

Short tandem repeats (STRs) are used in forensic DNA analysis because:

Accepted Answer

They vary in the number of repeats between individuals, allowing for unique DNA fingerprinting

Question 9

If an individual has alleles 14 and 16 for the D3S1358 STR locus, what does this mean?

Accepted Answer

The individual has 14 and 16 repeats of the AGAT sequence at this locus, one from each parent

Question 10

Which equation best describes the exponential amplification of DNA during PCR?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 11

A forensic DNA profile is generated by analyzing multiple STR loci. If the probability of two individuals sharing the same profile at one locus is $$1/17$$, and at a second locus is $$1/100$$, what is the probability they share the same profile at both loci?

Accepted Answer

$$1/1700$$

Question 12

Why is it important to use a control sample in diagnostic PCR tests, such as those for COVID-19?

Accepted Answer

To verify that the reagents are not contaminated and the test is working properly

Question 13

Which of the following best explains why PCR is considered an extraordinarily sensitive method for detecting viruses?

Accepted Answer

PCR can amplify trace amounts of nucleic acid, making even a single molecule detectable

Question 14

In gel electrophoresis, what determines the position of a DNA band?

Accepted Answer

The number of repeats at an STR locus, which affects the length of the DNA fragment

Question 15

Which step in PCR involves the hybridization of primers to the template DNA?

Accepted Answer

Annealing

Question 16

A microvariant allele at an STR locus is best described as:

Accepted Answer

An allele with a partial repeat sequence, not a complete integer number of repeats

Question 17

What is the function of dNTPs in a PCR reaction?

Accepted Answer

They provide the building blocks for new DNA strand synthesis

Question 18

Which of the following scenarios best illustrates the use of PCR in forensic science?

Accepted Answer

Amplifying STR loci from a hair sample to compare with a suspect's DNA profile

Question 19

If a PCR reaction is run for 7 cycles, starting with 1 double-stranded DNA molecule, how many double-stranded DNA molecules will be produced?

Accepted Answer

$$2^7 = 128$

Polymerase Chain Reaction (PCR): Principles, Applications, and Interpretation

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