Incomplete Dominance Punnett Square: Worked Example

📚 Quick Study Guide

• 🧬 Incomplete Dominance: A type of inheritance where the heterozygous genotype results in a phenotype that is a blend of the two homozygous phenotypes. Think of it like mixing paint!
• 📝 Punnett Square Basics: A tool used to predict the possible genotypes and phenotypes of offspring in a genetic cross.
• ✍️ Genotype Symbols: Capital letters represent dominant alleles, and lowercase letters represent recessive alleles. In incomplete dominance, we often use the same letter with different superscripts (e.g., $R^1$, $R^2$).
• 🧮 Example: If red flowers ($R^1R^1$) are crossed with white flowers ($R^2R^2$) in incomplete dominance, the heterozygous offspring ($R^1R^2$) will be pink.
• 📊 Phenotype Ratio: Analyzing the Punnett square helps determine the expected ratio of phenotypes in the offspring.

🧪 Practice Quiz

1. What is incomplete dominance?
   1. A. When one allele is completely dominant over another.
   2. B. When the heterozygous phenotype is a blend of the two homozygous phenotypes.
   3. C. When both alleles are equally expressed.
   4. D. When a gene has more than two alleles.
2. In a plant where flower color exhibits incomplete dominance, red flowers ($R^1R^1$) are crossed with white flowers ($R^2R^2$). What color are the heterozygous offspring?
   1. A. Red
   2. B. White
   3. C. Pink
   4. D. Red and White striped
3. If two pink flowers ($R^1R^2$) are crossed, what percentage of the offspring are expected to be white ($R^2R^2$)?
   1. A. 0%
   2. B. 25%
   3. C. 50%
   4. D. 75%
4. Which of the following genotypes represents a heterozygous individual in incomplete dominance?
   1. A. $R^1R^1$
   2. B. $R^2R^2$
   3. C. $R^1R^2$
   4. D. $R^1R^1R^2$
5. In chickens, feather color shows incomplete dominance. Black chickens ($B^1B^1$) crossed with white chickens ($B^2B^2$) produce grey offspring ($B^1B^2$). If two grey chickens are mated, what is the probability of producing a black chick?
   1. A. 0%
   2. B. 25%
   3. C. 50%
   4. D. 75%
6. What is the phenotypic ratio of the offspring if you cross a pink flower ($R^1R^2$) with a white flower ($R^2R^2$) in incomplete dominance?
   1. A. 1 Red : 2 Pink : 1 White
   2. B. 1 Red : 1 Pink : 0 White
   3. C. 0 Red : 1 Pink : 1 White
   4. D. 1 Red : 0 Pink : 1 White
7. In snapdragons, flower color is incompletely dominant. A cross between a $C^RC^R$ (red) flower and a $C^WC^W$ (white) flower produces $C^RC^W$ offspring. What color are the $C^RC^W$ offspring?
   1. A. Red
   2. B. White
   3. C. Pink
   4. D. Red and White striped