Question 1

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

Accepted Answer

Denaturation; 94-98°C

Question 2

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

Accepted Answer

Taq polymerase is not denatured by the high temperatures used during denaturation

Question 3

During PCR, what is the function of the primers?

Accepted Answer

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

Question 4

If a PCR reaction starts with 1 double-stranded DNA molecule, how many double-stranded DNA molecules will be present after 4 cycles, assuming perfect efficiency?

Accepted Answer

$$2^4 = 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 before PCR amplification?

Accepted Answer

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

Question 7

What is the main reason that PCR is considered an extraordinarily sensitive method for detecting trace amounts of viral genomes?

Accepted Answer

It amplifies the signal from every molecule of nucleic acid exponentially

Question 8

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

Accepted Answer

They vary in the number of repeats at each locus among individuals

Question 9

A forensic DNA profile examines multiple STR loci. If the probability of two random individuals sharing the same fingerprint at one locus is $$1/17$$, and at another locus is $$1/100$$, what is the probability they share the same fingerprint at both loci?

Accepted Answer

$$1/1700$$

Question 10

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

Accepted Answer

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

Question 11

Which equation best describes the exponential amplification of DNA during PCR, where $$n is $$the number of cycles and $$N_0 is $$the initial number of DNA molecules?

Accepted Answer

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

Question 12

Which of the following best explains why PCR can be used for paternity testing?

Accepted Answer

PCR can detect unique STR patterns inherited from both parents

Question 13

What would happen if the primers used in PCR were not specific to the target DNA sequence?

Accepted Answer

Multiple, non-specific DNA fragments would be amplified

Question 14

In a PCR reaction, what is the role of dNTPs?

Accepted Answer

They serve as the building blocks for new DNA strands

Question 15

A sample contains a single molecule of viral RNA. After reverse transcription and 10 cycles of PCR, how many molecules of cDNA would you expect, assuming perfect efficiency?

Accepted Answer

$$2^{10} = 1024$

Question 16

Which of the following statements about STR analysis in forensic science is TRUE?

Accepted Answer

The more STR loci analyzed, the lower the probability of two individuals sharing the same DNA fingerprint

Question 17

If a DNA sample is contaminated with DNA from multiple individuals, what is the most likely outcome when performing STR analysis?

Accepted Answer

Multiple bands will appear for each STR locus, representing the alleles from all individuals

Question 18

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

Accepted Answer

Annealing

Question 19

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

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

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