Objective: 

To cross F1 seeds from a purple/hairy and non-purple/non-hairy cross and determine if the outcome follows Gregor Mendel’s dihybrid cross results.

Materials (per group):

Watering system, 8 quads with watering diamonds, label stakes, fertilizer pellets, growing medium, ties, pollinating sticks,  F1 seeds, copper sulphate

Planting Procedure: 

  1. Soak a watering diamond and put into one section of the quad so that about half of it sticks out the bottom. Repeat for the rest of the quad.
  2. Add growing medium until the quad is ½ full, add 3 fertilizer pellets.
  3. Add growing medium until the quad is full. Tap the quad on the counter to settle the growing medium, add more to bring it back to the top.
  4. Soak the growing medium until water is dripping out the bottom.
  5. Place 1 seed, on the growing medium in the middle, in each of the 4 sections of the quad, gently push the seed into the wet growing medium.
  6. Sprinkle dry growing medium to just cover the seeds.
  7. Soak again.
  8. Repeat for the other 7 quads.
  9. Fill the watering tray with tap water to the fill line.
  10. Place the watering mat in the tray to soak it.
  11. Remove the mat, snap the lid on the tray and place the mat on the lid so the narrow end extends down into the water.
  12. Place the quads on top of the mat.
  13. Place the tray in the chamber.
  14. Check the pots daily to determine germination.  Once seeds have germinated make observations of the seedlings. Look for colours, size, shape; of leaves and stem.
  15. Add 10 mL of copper sulphate to the watering system tray on day 10.
  16. At about day 13 the plants will be ready for pollination. The plants will be pollinated in pairs.
  17. Day 13 to 16: Pollination.  Swirl the pollinating stick around in the open flower, trying to pick up the pollen from the anthers.  Go to an open flower on the other plant and repeat the swirling.  Go back to a different flower on the first plant.  Repeat for all flowers on the two plants.  This process will be repeated for three days during flowering. Use label stakes to keep track of the pollinated plants.
  18. After the last pollination, the tip of the plant above the top flower should be pinched or cut off.  Any developing buds or flowers that have not been pollinated should also be removed.
  19. After 20 more days the plants will be removed from the water and left dry for 5 days.
  20. After 5 days remove the seeds from the pods and repeat steps 1-15.
  21. Summarize the results.
  22. Calculate the expected results for your cross. Compare these to your actual results using a Chi Square test.

Results:

Design tables to record observations and data in your lab book.

Analysis:

Do the results and analysis support Mendel’s work and theories? Support your answer.

Contributed by David Prescott, Head of Science Faculty, St. John's-Ravenscourt School