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

What is the primary function of the primers in a PCR reaction?

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 a typical eukaryotic DNA polymerase?

Accepted Answer

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

Question 4

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

Accepted Answer

32

Question 5

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 6

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

Accepted Answer

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

Question 7

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

Accepted Answer

RNA polymerase

Question 8

Gel electrophoresis is used after PCR to separate DNA fragments. What determines the position of a DNA band in the gel?

Accepted Answer

The number of repeats at an STR locus

Question 9

In forensic DNA analysis, why are short tandem repeats (STRs) used for DNA fingerprinting?

Accepted Answer

STRs are highly variable in the population, making them useful for distinguishing individuals

Question 10

A forensic sample is analyzed at 10 STR loci. If the probability of two random individuals sharing the same fingerprint at one locus is $$1/17$$, what is the probability they share the same fingerprint at all 10 loci?

Accepted Answer

$$1/17^{10}$$

Question 11

Which step in PCR involves cooling the sample to allow primers to bind to their complementary sequences?

Accepted Answer

Annealing

Question 12

What is the function of dNTPs in a PCR reaction?

Accepted Answer

They provide the building blocks for new DNA strand synthesis

Question 13

In a gel electrophoresis analysis of STR loci, an individual shows two bands for a locus. What does this indicate?

Accepted Answer

The individual inherited different repeat numbers from each parent

Question 14

Which of the following best explains why PCR is an extraordinarily sensitive method for detecting trace amounts of viral genomes?

Accepted Answer

PCR can amplify even a single molecule of nucleic acid exponentially

Question 15

A PCR reaction is set up to amplify a region of DNA. After 7 cycles, how many DNA molecules will be produced from a single starting molecule, assuming perfect efficiency?

Accepted Answer

128

Question 16

Which of the following statements about PCR is FALSE?

Accepted Answer

PCR can amplify both DNA and RNA directly without any modifications

Question 17

In paternity testing, why is it important to analyze multiple STR loci?

Accepted Answer

To reduce the chance that two unrelated individuals share the same DNA fingerprint

Question 18

What is the significance of microvariant alleles in STR analysis?

Accepted Answer

They indicate partial repeats and help distinguish alleles that are not exact integer counts

Question 19

Which of the following best describes the role of gel electrophoresis in PCR-based forensic analysis?

Accepted Answer

It separates DNA fragments based on their size, allowing identification of STR alleles

Question 20

A sample contains two alleles at the D3S1358 locus: 14 and 16. If the population frequency for 14,16 is $$1/17$$ and for another locus (Penta E) the frequency for 11,19 is $$1/100$$, what is the combined probability of randomly matching both loci?

Accepted Answer

$$1/1700$$

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

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