Real-world examples of incomplete dominance in animals and plants.

📚 Quick Study Guide

• 🧬 Incomplete dominance is a type of inheritance where the heterozygous genotype results in a phenotype that is intermediate between the two homozygous phenotypes.
• 🌸 Unlike complete dominance, one allele does not completely mask the other.
• 🐔 A classic example is the feather color in chickens: black (BB), white (bb), and blue (Bb).
• 🌺 In plants, flower color in snapdragons shows incomplete dominance: red (RR), white (rr), and pink (Rr).
• 🌱 The phenotypic ratio in the offspring of two heterozygous parents is typically 1:2:1.
• 🧪 It's important to distinguish incomplete dominance from codominance, where both alleles are expressed simultaneously.
• 💡 Understanding incomplete dominance helps predict the traits of offspring based on parental genotypes.

Practice Quiz

1. Which of the following is the best definition of incomplete dominance?
   1. A) One allele completely masks the other.
   2. B) Both alleles are expressed simultaneously.
   3. C) The heterozygous phenotype is intermediate between the two homozygous phenotypes.
   4. D) The heterozygote expresses both homozygous phenotypes.
2. In snapdragons, red flower color (RR) is incompletely dominant to white flower color (rr). What color are the flowers of a plant with the genotype Rr?
   1. A) Red
   2. B) White
   3. C) Pink
   4. D) Red and White
3. In chickens, the allele for black feathers (B) and the allele for white feathers (b) exhibit incomplete dominance. What feather color would you expect in a Bb chicken?
   1. A) Black
   2. B) White
   3. C) Blue
   4. D) Black and White
4. If two pink snapdragons (Rr) 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 : 1 Pink : 2 White
   4. D) 2 Red : 1 Pink : 1 White
5. Which of the following is an example of incomplete dominance in animals?
   1. A) Human blood type (ABO system)
   2. B) Coat color in horses where roan color is observed (mixture of red and white hairs)
   3. C) Feather color in chickens (black, white, and blue)
   4. D) Eye color in humans (brown and blue)
6. How does incomplete dominance differ from codominance?
   1. A) In incomplete dominance, one allele masks the other completely.
   2. B) In codominance, the heterozygous phenotype is intermediate.
   3. C) In incomplete dominance, the heterozygous phenotype is intermediate, while in codominance, both alleles are fully expressed.
   4. D) There is no difference between incomplete dominance and codominance.
7. A plant with genotype $C^RC^W$ shows flowers that are neither fully red nor fully white, but a blend of the two (pink). This is an example of:
   1. A) Complete dominance
   2. B) Codominance
   3. C) Incomplete dominance
   4. D) Epistasis