Question 1

What does DNA stand for?

Accepted Answer

DNA stands for Deoxyribonucleic Acid.

Question 2

What are the four nitrogen bases found in DNA?

Accepted Answer

Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

Question 3

What is gel electrophoresis used for?

Accepted Answer

Gel electrophoresis is used to separate DNA fragments by size using an electric current.

Question 4

What is base pairing in DNA?

Accepted Answer

Base pairing is the rule that Adenine always pairs with Thymine (A-T) and Guanine always pairs with Cytosine (G-C), held together by hydrogen bonds.

Question 5

Which direction do DNA fragments move during electrophoresis?

Accepted Answer

DNA fragments move toward the positive electrode (anode) because DNA is negatively charged.

Question 6

Do smaller or larger DNA fragments travel farther in the gel?

Accepted Answer

Smaller fragments travel farther because they move more easily through the gel matrix.

Question 7

What is a restriction enzyme?

Accepted Answer

A restriction enzyme is a protein that cuts DNA at specific recognition sequences, producing fragments of different sizes used in gel electrophoresis.

Question 8

Why is a DNA ladder (marker) used in gel electrophoresis?

Accepted Answer

A DNA ladder contains fragments of known sizes and is run alongside samples to estimate the size of unknown DNA fragments by comparison.

Question 9

What does it mean if two DNA samples produce identical band patterns?

Accepted Answer

Identical band patterns indicate the DNA fragments are the same size, suggesting the samples may come from the same individual or closely related sources.

Question 10

What is DNA fingerprinting?

Accepted Answer

DNA fingerprinting is a technique that analyzes specific regions of DNA (STRs) to create a unique profile for an individual, used in forensics, paternity testing, and identification.

Question 11

What are STRs (Short Tandem Repeats)?

Accepted Answer

STRs are short sequences of DNA that repeat multiple times; the number of repeats varies between individuals, making them useful for identification.

Question 12

How is DNA fingerprinting used in criminal investigations?

Accepted Answer

DNA from a crime scene (blood, hair, saliva) is extracted, amplified using PCR, and run through gel electrophoresis. The resulting band pattern is compared to suspects' DNA profiles.

Question 13

Can identical twins be distinguished by DNA fingerprinting?

Accepted Answer

No — identical twins have the same DNA sequence, so their DNA fingerprints are identical. Other methods must be used to distinguish them.

Question 14

What is PCR used for?

Accepted Answer

PCR (Polymerase Chain Reaction) is used to amplify (make millions of copies of) a specific DNA segment from a very small sample.

Question 15

What are the three steps of PCR?

Accepted Answer

Denaturation (DNA strands separate at ~95°C), Annealing (primers attach to target sequences at ~55°C), and Extension (DNA polymerase builds new strands at ~72°C).

Question 16

Why is PCR important for forensic analysis?

Accepted Answer

PCR allows scientists to amplify tiny amounts of DNA from crime scenes (a single hair or drop of blood) into enough material for analysis.

Question 17

A DNA sample produces bands at 500, 1000, and 2000 base pairs. A suspect's sample produces bands at 500 and 2000 bp. Could the suspect be the source?

Accepted Answer

No — the suspect's sample is missing the 1000 bp band. For a match, all bands must align. The suspect is likely not the source of the crime scene DNA.

Question 18

Why is DNA evidence considered highly reliable in court?

Accepted Answer

The probability of two unrelated individuals having identical DNA profiles across multiple STR loci is extremely small (often less than 1 in a billion), making DNA evidence highly reliable.

Question 19

What ethical concerns surround DNA databases?

Accepted Answer

Concerns include privacy (who has access to your DNA), potential misuse by governments or corporations, discrimination based on genetic information, and consent issues around familial searching.

DNA Analysis Answer Key

Prior Knowledge Questions

Activity A – Gel Electrophoresis

Activity B – DNA Fingerprinting

Activity C – PCR (Polymerase Chain Reaction)

Assessment Questions

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