Question 1

Which of the following best explains why DNA profiling typically analyzes non-coding regions (introns) rather than exons?

Accepted Answer

Non-coding regions contain more repetitive sequences and variations, making them more useful for distinguishing individuals.

Question 2

A forensic scientist is analyzing a DNA sample using PCR-based Short Tandem Repeat (STR) analysis. Which property of STRs makes them especially useful for individual identification?

Accepted Answer

The number of repeat units at each STR locus varies greatly among individuals.

Question 3

During the PCR process, what is the primary function of the primers?

Accepted Answer

They bind to specific target sequences, providing a starting point for DNA synthesis.

Question 4

Which of the following best describes the movement of DNA fragments during gel electrophoresis?

Accepted Answer

DNA fragments move toward the positive electrode, with shorter fragments traveling farther than longer ones.

Question 5

A crime scene DNA sample is compared to three suspects using gel electrophoresis. The suspect whose DNA banding pattern matches the crime scene sample is most likely to be:

Accepted Answer

The individual whose DNA fragments create bands at the same positions as the crime scene sample.

Question 6

Which of the following is a key advantage of PCR-based DNA profiling over RFLP analysis?

Accepted Answer

PCR can amplify DNA from very small or degraded samples, while RFLP requires large amounts of high-quality DNA.

Question 7

Which enzyme is responsible for synthesizing new DNA strands during the extension step of PCR, and why is it suitable for this process?

Accepted Answer

Taq polymerase; it is heat-resistant and can function at high temperatures.

Question 8

If a DNA sample undergoes 30 cycles of PCR, and each cycle doubles the amount of target DNA, how many times greater is the final amount of DNA compared to the starting amount? (Assume perfect efficiency.)

Accepted Answer

$$2^{30}$$ times greater

Question 9

Which of the following statements about the Combined DNA Index System (CODIS) is correct?

Accepted Answer

CODIS is a national database that stores DNA profiles for comparison in forensic investigations.

Question 10

A student sets up a gel electrophoresis experiment but accidentally reverses the electrodes, placing the DNA wells near the positive electrode. What is the most likely outcome?

Accepted Answer

DNA fragments will move toward the negative electrode, away from the wells, and may not enter the gel.

Question 11

Which step in the PCR process is responsible for separating the two strands of the DNA double helix?

Accepted Answer

Denaturation

Question 12

Why is the likelihood of a random match between two unrelated individuals' DNA profiles using 13 to 20 STR markers less than one in a trillion?

Accepted Answer

The probability of two people sharing the same combination of STR repeat numbers at so many loci is extremely low.

Question 13

A forensic technician is analyzing a degraded DNA sample from a crime scene. Which method would be most effective for generating a DNA profile?

Accepted Answer

PCR-based STR analysis

Question 14

Which of the following best describes the role of restriction enzymes in RFLP analysis?

Accepted Answer

They cut DNA at specific recognition sequences, generating fragments of varying lengths.

Question 15

In a real-world paternity case, why is it important to analyze multiple STR loci rather than just one?

Accepted Answer

Analyzing multiple loci greatly reduces the probability of a coincidental match, increasing the accuracy of identification.

Question 16

Which of the following best explains why shorter DNA fragments travel farther in an agarose gel during electrophoresis?

Accepted Answer

Shorter fragments can move more easily through the pores of the gel matrix.

Question 17

A laboratory is comparing two DNA samples using RFLP analysis. If both samples are cut with the same restriction enzyme but produce different fragment patterns, what is the most likely explanation?

Accepted Answer

The DNA sequences differ at the restriction sites, resulting in different fragment lengths.

Question 18

Which of the following is NOT a correct step in the PCR cycle?

Accepted Answer

Ligation: joining DNA fragments together

Question 19

A medical diagnostic lab uses PCR to detect a genetic marker associated with a disease. If the marker is present, a specific DNA fragment is amplified and visualized as a band on a gel. What does the presence of this band indicate?

Accepted Answer

The patient carries the genetic marker associated with the disease.

Question 20

Which of the following best describes the function of the agarose gel in gel electrophoresis?

Accepted Answer

It acts as a molecular sieve, separating DNA fragments by size.

DNA Profiling: Techniques and Applications in Forensic Biology

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