Codominance Examples: Roan Cattle, Human Blood Types, and More

📚 Quick Study Guide

• 🧬 Codominance Definition: A form of inheritance where both alleles for a trait are equally expressed. Neither allele is dominant or recessive.
• 🐮 Roan Cattle Example: A roan cow has both red and white hairs, showing both traits simultaneously. The genotype $CRCW$ results in a mix of red ($CR$) and white ($CW$) hairs.
• 🩸 Human Blood Types Example: For blood type AB, both A and B alleles are expressed. The genotype $IAIB$ results in both A and B antigens being present on the red blood cells.
• 🔬 Key Characteristics: No blending occurs; both traits are fully and independently expressed.
• 💡 Contrast with Incomplete Dominance: In incomplete dominance, traits blend (e.g., red and white flowers make pink flowers), whereas in codominance, both traits appear distinctly.
• 📝 Genotype Notation: Codominance is often represented using superscript letters to denote the different alleles (e.g., $CR$, $CW$, $IA$, $IB$).

🧪 Practice Quiz

1. Which of the following is the best example of codominance?
   1. Black and white spots in chickens.
   2. Red and white flowers producing pink flowers.
   3. Tall pea plants crossed with short pea plants producing medium height plants.
   4. Brown eyes being dominant over blue eyes.
2. In roan cattle, the coat color is codominant. What phenotypes would you expect from a cross between a roan bull and a white cow?
   1. All roan.
   2. 50% roan, 50% white.
   3. 75% roan, 25% white.
   4. 50% red, 50% white.
3. A woman with type AB blood marries a man with type O blood. What are the possible blood types of their children?
   1. A, B, or O.
   2. AB or O.
   3. A or B.
   4. Only AB.
4. What is the genotype for a person with type AB blood?
   1. $IAIA$
   2. $IBIB$
   3. $IAIB$
   4. $ii$
5. Which of the following is NOT a characteristic of codominance?
   1. Both alleles are expressed.
   2. Neither allele is dominant or recessive.
   3. The heterozygous phenotype is an intermediate blend of the two homozygous phenotypes.
   4. Both homozygous phenotypes are expressed.
6. In some chickens, the allele for black feathers (B) and the allele for white feathers (W) are codominant. What color would you expect a chicken with the genotype BW to be?
   1. Black.
   2. White.
   3. Gray.
   4. Black and white spotted.
7. How does codominance differ from incomplete dominance?
   1. In codominance, one allele is dominant, while in incomplete dominance, neither allele is dominant.
   2. In codominance, both alleles are fully expressed, while in incomplete dominance, the phenotype is a blend of both alleles.
   3. Codominance only occurs in animals, while incomplete dominance only occurs in plants.
   4. Codominance involves multiple genes, while incomplete dominance involves only one gene.