What is gel electrophoresis? Explain how DNA fragments are separated, seen and recovered, with a labelled diagram.

1. 1 · Define in one line. Gel electrophoresis separates DNA fragments by size by making them move through a gel in an electric field.
2. 2 · State the principle. DNA is negatively charged, so it moves towards the anode.
3. 3 · Explain separation. Agarose, from seaweeds, acts as a sieve; smaller fragments move farther.
4. 4 · Explain how bands are seen. Stain with ethidium bromide and expose to UV light: bright orange bands.
5. 5 · Explain recovery. Cut out the band and extract the DNA (elution); join it to a vector.
6. 6 · Draw the gel. [Diagram: gel with wells at the cathode end, numbered lanes, bands, arrow towards the anode]
7. 7 · Link to real life. Used in forensic DNA fingerprinting and to check PCR tests in diagnosis.
8. 8 · Close in one line. So electrophoresis isolates the exact fragment needed to build recombinant DNA.

Scoring tip: Mark the + and − ends and the wells. Write 'ethidium bromide' and 'UV' together.