Dominance and Recessiveness with Food Coloring

This demonstration uses colored water, bleach, and food coloring to model how dominant, recessive, and codominant traits are expressed. By mixing colors in different combinations, students see how phenotypes appear in offspring.

1. Fill two small glasses with red-colored water and two more with plain water.
2. Show three empty large glasses to the class (one should secretly contain 1 mL of bleach).
3. Pour the two red glasses into the first large glass—result: red phenotype (homozygous red).
4. Pour the two clear glasses into the second large glass—result: clear phenotype (homozygous clear).
5. Pour one red glass and one clear glass into the third glass (with bleach)—result: clear solution, representing a heterozygote where the clear trait is dominant.
6. For codominance, prepare one small glass with red water and another with yellow water.
7. Pour them together into a large glass—result: orange solution, representing codominance or blending inheritance.

📄 DOMINANCE AND RECESSIVNESS (Page 10) - Shannon Winter: https://www.unco.edu/nhs/science/pdf/demos/2006_CSC.pdf

• Expand the analogy by creating Punnett squares and comparing predicted vs. observed “phenotypes.”

• Handle bleach carefully—only use a very small amount (1 mL) and keep away from skin, eyes, and clothing.
• Clearly label the bleach-containing glass before setup to avoid accidents.
• Wear safety glasses and gloves if handling bleach directly.
• Dispose of bleach solutions safely by diluting with plenty of water before discarding.

• Why does the clear water represent the dominant trait in this analogy? (Because it masks the presence of the red when combined with bleach.)
• How is codominance represented in the red and yellow mixture? (Neither color dominates, and both traits are visible as a blended orange.)
• What is the difference between dominance and codominance in genetics? (Dominance means one allele masks the other, while codominance means both alleles are expressed together.)
• How does this demonstration simplify the real complexity of genetics? (It uses visible color mixing as an analogy, but real genetic dominance involves proteins and biochemical pathways.)