DNA Technology Quiz
Questions: 16 · 10 minutes
1. In a typical CRISPR-Cas9 system, what primarily directs Cas9 to a complementary DNA target?
A guide RNA
A DNA ligase molecule
A fluorescent reporter protein
A selectable marker
2. After CRISPR editing, sequencing reveals an unintended change at a similar DNA sequence elsewhere in the genome. What is this called?
Directional cloning
Complementary DNA synthesis
A selectable phenotype
An off-target edit
3. A human protein-coding gene contains several introns. Why is cDNA often used instead of genomic DNA when producing the protein in bacteria?
cDNA represents processed RNA and therefore lacks the introns bacteria generally cannot remove
cDNA automatically supplies a bacterial promoter and ribosome-binding site
cDNA is made of amino acids and can be translated immediately
cDNA prevents every possible mutation during bacterial growth
4. Researchers attempt to insert a transgene at a specific genomic location. Which result gives the strongest evidence that the transgene joined the intended site rather than merely being present elsewhere?
The cells survive antibiotic selection
A reporter protein is visible in some cells
PCR using one primer outside the target region and one inside the transgene produces the expected junction fragment
PCR detects a sequence located entirely within the transgene
5. After DNA fragments are separated on a gel, a researcher needs to detect fragments containing one particular sequence. Which method is designed for this purpose?
Western blotting with an antibody
Bacterial transformation with a plasmid
Southern blotting with a complementary nucleic acid probe
Protein purification by affinity chromatography
6. What is the primary purpose of the polymerase chain reaction (PCR)?
To separate DNA fragments according to size
To make many copies of a selected DNA region
To join DNA fragments into a continuous molecule
To translate a gene directly into protein
7. Why do dideoxynucleotides terminate DNA strand extension in traditional Sanger sequencing?
They bind permanently to the DNA template before synthesis begins
They cut the newly synthesized strand at a specific base
They prevent primers from pairing with the template
They lack the 3′ hydroxyl group needed to add the next nucleotide
8. Two linear DNA fragments measuring 500 and 2,000 base pairs are placed in the same agarose gel. Under standard conditions, what result is expected?
The 500-base-pair fragment moves farther because it passes through the gel matrix more easily
Both fragments move the same distance because DNA has a uniform charge-to-mass ratio
The 2,000-base-pair fragment moves farther because it carries more charge
The 500-base-pair fragment remains in the well because short DNA cannot enter the gel
9. In bacterial genetic engineering, what does transformation mean?
The uptake of external genetic material by a bacterial cell
The conversion of messenger RNA into protein at a ribosome
The separation of DNA fragments using an electric field
The cutting of DNA at a restriction site
10. A researcher has placed a DNA insert beside an opened plasmid, and the two molecules have compatible ends. Which enzyme directly seals the breaks in the sugar-phosphate backbone?
DNA polymerase
DNA ligase
Reverse transcriptase
Restriction endonuclease
11. A scientist wants to express a human gene in bacteria but needs a version without introns. Which starting method is most suitable?
Digest genomic DNA with a single restriction enzyme
Use reverse transcriptase to make cDNA from mature mRNA
Separate the human chromosomes by gel electrophoresis
Copy the promoter region with DNA ligase
12. Two biological samples are compared using several short tandem repeat (STR) regions. What provides the basis for distinguishing the samples?
Every STR region is identical in all members of a species
STR analysis measures which proteins each sample currently produces
Individuals can differ in the number of repeat units at multiple STR loci
STR analysis determines the complete sequence of every chromosome
13. Two samples are tested with the same efficient quantitative PCR assay. Sample A crosses the fluorescence threshold at cycle 18, while Sample B crosses it at cycle 25. What is the usual inference?
Sample B had more starting target because it required more cycles
Sample A lacked a sequence complementary to the primers
Both samples necessarily contained identical starting amounts
Sample A likely contained more starting target DNA
14. A researcher cuts a plasmid and an insert with two different restriction enzymes, producing a different overhang at each end. What is a major advantage of this strategy?
It converts the inserted DNA into RNA before ligation
It allows the plasmid to replicate without an origin of replication
It removes the need to screen for bacteria carrying a plasmid
It encourages the insert to ligate in one defined orientation
15. A no-template control in a PCR experiment produces a clear amplification band. What is the best interpretation?
The target DNA was present at a very high concentration
The primers successfully distinguished genomic DNA from cDNA
The reagents or setup were probably contaminated with amplifiable DNA
The DNA ladder entered the control reaction
16. Bacteria are transformed with a plasmid carrying an antibiotic-resistance marker and then spread on medium containing that antibiotic. What is the main purpose of the antibiotic?
To increase the rate at which bacteria take up plasmid DNA
To select for bacteria that received and express the plasmid marker
To cut the plasmid at its cloning site
To reveal the exact nucleotide sequence of the insert