Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Biology
Lesson Topic: describe and explain how gel electrophoresis is used to separate DNA fragments of different lengths
Learning Objective/s:
  • Describe the principle of gel electrophoresis and how DNA fragments migrate in an electric field.
  • Explain how gel composition, voltage, and buffer affect the separation of DNA fragments of different lengths.
  • Interpret electrophoresis results by comparing sample bands to a DNA ladder and estimate fragment sizes.
  • Evaluate factors that influence resolution and suggest appropriate conditions for specific fragment size ranges.
Materials Needed:
  • Agarose powder and casting trays with combs
  • TAE or TBE running buffer
  • Power supply with adjustable voltage
  • Electrophoresis chamber and gel casting equipment
  • Micropipettes and tips
  • Loading dye and DNA ladder
  • UV transilluminator or blue‑light imager with safety goggles
  • Worksheet or digital slides for diagram labeling
 Introduction:
Begin with a short video showing DNA fragments separating on a gel, asking students what they notice about the band patterns. Recall that DNA is negatively charged and that size influences migration in an electric field. Today students will demonstrate how gel electrophoresis separates fragments and will be able to describe the key components, explain the role of gel concentration and voltage, and interpret a gel image to estimate fragment sizes.
Lesson Structure:
  1. Do‑now (5'): Quick quiz on DNA charge and previous lab work.
  2. Mini‑lecture (10'): Introduce gel electrophoresis principle and apparatus using slides.
  3. Demonstration (15'): Teacher prepares and pours agarose gel, sets comb, and explains each step.
  4. Hands‑on activity (20'): Students set up chambers, load DNA samples with loading dye and a DNA ladder, then run the gel at a set voltage.
  5. Visualization & analysis (10'): Stain gel, view under UV/blue light, record band positions and estimate fragment sizes using the ladder.
  6. Guided discussion (5'): Students explain how gel concentration and voltage affected separation and suggest improvements.
Conclusion:
Summarise how the electric field and gel matrix work together to separate DNA fragments by size. For the exit ticket, each student writes one factor that could improve resolution and explains why. Assign homework to read a case study on using electrophoresis for genotyping and prepare a short report on the technique’s application.