Lesson Hook: "Dominance and Recessiveness"

Objective

To show by analogy the difference between dominant/recessive and co-dominant.

Materials

• 6 small drinking glasses
• 4 large drinking glasses
• Water
• Red food colouring
• Bleach
• Yellow food colouring

Procedure:

First Experiment

1.   Fill two small glasses with water coloured a deep red with food coloring

2.   Fill two more small glasses with plain water

3.   Now pour some of the red solution from each of the two glasses (parent genes) into the first large glass (F1 generation)
(a) Predict what will happen when the red solutions are poured into the larger glass.

4.   Repeat for the two glasses of clear water
(a) Predict what will happen when the water solutions are poured into the larger glass.

5.   Now pour simultaneously from both the red and water glasses into the third glass (with the bleach). (a) Predict what will happen to the solutions from the red and water is poured together.

Second Experiment

6.   Fill one small glass with red water

7.   Fill the other small glass with yellow water

8.   Pour the two solutions together into larger glass. (a) predict what will happen when these two solutions are poured together.

Explanation

First Experiment - Point out three apparently empty larger glasses (In the third of these, there should be 1 ml of bleach, put there before class).  The red and clear waters represent genes. For the first mixture (2 red small glasses in one large one) the solution is still red, showing that the phenotype for two homozygous genes is the same as that of the parents.  The above also applies for the 2 water small glasses in the big one. When the large red glass and the large clear water glass are poured simultaneously together int the glass with the bleach the resulting solution (heterozygous) will be clear showing the trait of only one parent.   This indicates the water solution (gene) is the dominant one.

Second Experiment - Results in orange water coloured solution that represents co-dominance or blending inheritance in the F1 generation.  Neither of the two genes (colours) was dominant over the other.

Why is this a worthwhile Lesson Hook Activity?

This is a worthwhile lesson hook activity because it attracts the focus of students when the red water and clear water are mixed with the bleach and becomes clear.  The students will not know why this happened and may ask for it to be shown again.  The students will be able to see a physical interpretation of what occurs in F1 generations.  Since this topic is somewhat difficult for many students to conceptualize on paper, this will help with their understanding of recessive, dominant, and co-dominant.