Examples of incomplete dominance traits.

📚 Quick Study Guide

• 🧬 Incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes.
• 🌸 Unlike complete dominance, neither allele is fully dominant over the other.
• 🎨 The heterozygous offspring display a blended phenotype. Think of mixing paint – red + white = pink.
• 🌱 A classic example is the flower color in snapdragons.
• 🐔 Feather color in some chicken breeds also exhibits incomplete dominance.
• 📝 Genotypic and phenotypic ratios in the F2 generation are often the same (1:2:1).
• ➗ If $R$ represents the allele for red flowers and $W$ represents the allele for white flowers, $RW$ individuals will have pink flowers.

Practice Quiz

1. What is incomplete dominance?
1. A) One allele completely masks the other.
2. B) The heterozygous phenotype is a blend of the homozygous phenotypes.
3. C) Both alleles are expressed equally.
4. D) The dominant allele is always expressed.
2. In snapdragons, a red flower ($RR$) is crossed with a white flower ($WW$). What color are the heterozygous offspring ($RW$)?
1. A) Red
2. B) White
3. C) Pink
4. D) Red and White striped
3. If two pink snapdragons ($RW$) are crossed, what is the expected phenotypic ratio of the offspring?
1. A) 3 Red : 1 White
2. B) 1 Red : 2 Pink : 1 White
3. C) 1 Red : 3 Pink
4. D) All Pink
4. Which of the following is NOT a characteristic of incomplete dominance?
1. A) Blended phenotype in heterozygotes
2. B) 1:2:1 phenotypic ratio in the F2 generation
3. C) One allele completely masks the other
4. D) Neither allele is fully dominant
5. In certain chicken breeds, the allele for black feathers ($B$) and the allele for white feathers ($W$) exhibit incomplete dominance. Heterozygous chickens ($BW$) have blue feathers. If two blue chickens are crossed, what percentage of the offspring will be blue?
1. A) 25%
2. B) 50%
3. C) 75%
4. D) 100%
6. What is the genotype of a pink snapdragon if red ($R$) and white ($W$) show incomplete dominance?
1. A) $RR$
2. B) $WW$
3. C) $RW$
4. D) $RRWW$
7. A plant breeder crosses a true-breeding purple flower with a true-breeding white flower. The resulting offspring are all lavender. This is most likely an example of:
1. A) Complete dominance
2. B) Incomplete dominance
3. C) Codominance
4. D) Sex-linked inheritance