PCR and gel electrophoresis explains how DNA is copied, checked, amplified or analysed through specific strand relationships, enzymes and molecular techniques.
Coverage 2015–2025 · Updated 16 Jul 2026
PCR amplifies a selected DNA region; gel electrophoresis then separates DNA fragments mainly by length.
Primers define the target ends. Each thermal cycle uses high temperature to separate strands, lower temperature for primer binding, and a suitable extension temperature for heat-stable Taq DNA polymerase to synthesize new DNA.
Load amplified fragments into wells. Negatively charged DNA moves toward the positive electrode through the gel; shorter fragments move farther than longer fragments in the same time.
Primers amplify a variable DNA locus; electrophoresis separates the resulting fragments, and a size marker allows their approximate lengths to be compared.
PCR increases the amount of target DNA; electrophoresis separates fragments. Primer specificity, contamination controls and the size marker affect interpretation.
This objective is assessed through structured response, multiple choice, commonly using Explain / Outline / State.
Explain / Outline / State / Identify / Determine / Describe / Compare / Deduce / Predict / Suggest
Build the answer around this relationship: PCR and gel electrophoresis depends on matching each strand, enzyme or laboratory step to its exact function.
Describing PCR as DNA separation instead of DNA amplification.
Representative question
Describe the polymerase chain reaction (PCR).
DNA replication produces exact DNA copies before cell division and maintains genetic continuity for reproduction, growth, and tissue replacement. Semi-conservative replication gives each new DNA molecule one original strand and one new strand; complementary base pairing and Meselson-Stahl isotope evidence support the model. Helicase unwinds DNA and breaks hydrogen bonds; DNA polymerase joins complementary nucleotides to build new strands. PCR amplifies selected DNA using primers, temperature cycles, and Taq polymerase; gel electrophoresis separates DNA fragments by size and charge. PCR and gel electrophoresis support DNA profiling for forensic identification and paternity testing.
