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Unit 2: How does inheritance impact on diversity?
Quick questions on DNA manipulation: PCR and gel electrophoresis: VCE Biology Unit 2
14short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is polymerase chain reaction (PCR)?Show answer
PCR is a technique that amplifies a specific stretch of DNA from tiny starting amounts to millions of copies, fast enough to be useful in diagnostic, forensic and research settings. Invented by Kary Mullis (Nobel 1993).
What is gel electrophoresis?Show answer
Gel electrophoresis separates DNA fragments by size. Used to check PCR products, compare DNA profiles, or sort DNA pieces before sequencing.
What is dNA profiling?Show answer
DNA profiling (also called DNA fingerprinting) uses regions of the genome where individuals differ predictably.
What is other DNA manipulation tools (background)?Show answer
PCR and gel electrophoresis are the workhorses that underlie all of these.
What is outcome?Show answer
Each cycle doubles the amount of target DNA: 1 to 2 to 4 to 8 to ...
What is visualisation?Show answer
The amplified product is then loaded into a gel (next section) or sequenced.
What is strengths?Show answer
Extreme sensitivity (single molecules can be amplified), speed (a few hours from sample to product), and specificity (primers ensure only the target region is amplified).
What is limitations?Show answer
Sensitivity is also a weakness: contamination with stray DNA can be amplified just as easily as the target. PCR requires knowledge of the target sequence to design primers.
What is saying PCR "creates new genes"?Show answer
PCR copies existing DNA. It does not create new sequences.
What is calling Taq "any DNA polymerase"?Show answer
Taq is special because it is heat-stable. Ordinary DNA polymerase would denature at the high temperatures used for denaturation each cycle.
What is forgetting primers?Show answer
Without two specific primers, PCR has no idea what to copy. Primer design is the most important step in setting up a PCR.
What is saying "gel electrophoresis separates DNA by charge"?Show answer
All DNA fragments have the same charge-to-mass ratio (one negative charge per nucleotide). Separation in the gel is by size, mediated by the matrix.
What is loading at the positive end?Show answer
DNA loads at the negative end and migrates toward the positive electrode.
What is confusing PCR with sequencing?Show answer
PCR amplifies; sequencing reads the base order. They are often done in sequence (PCR first, then sequencing of the product), but they are different techniques.