Which statement best describes the difference between codominance and incomplete dominance?

• A. In codominance, both alleles are fully expressed in the phenotype, while in incomplete dominance, the phenotype is a blend of the two alleles.
• B. Both codominance and incomplete dominance result in the dominant allele being fully expressed over the recessive allele.
• C. In incomplete dominance, both alleles are fully expressed, while in codominance, the phenotype is a blend of the two alleles.
• D. In codominance, one allele completely masks the other, while in incomplete dominance, both alleles are fully expressed.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the key concepts of codominance and incomplete dominance. Codominance occurs when both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that shows both traits distinctly. For example, in blood type AB, both A and B alleles are expressed equally. In contrast, incomplete dominance occurs when the phenotype of a heterozygous organism is a blend or intermediate of the two alleles, such as a red flower crossed with a white flower producing pink offspring.
2. Step 2: Analyze the first statement: 'In codominance, both alleles are fully expressed in the phenotype, while in incomplete dominance, the phenotype is a blend of the two alleles.' This statement correctly describes the difference between codominance and incomplete dominance.
3. Step 3: Evaluate the second statement: 'Both codominance and incomplete dominance result in the dominant allele being fully expressed over the recessive allele.' This is incorrect because in both codominance and incomplete dominance, neither allele is completely dominant over the other.
4. Step 4: Evaluate the third statement: 'In incomplete dominance, both alleles are fully expressed, while in codominance, the phenotype is a blend of the two alleles.' This is incorrect because it reverses the definitions of codominance and incomplete dominance.
5. Step 5: Evaluate the fourth statement: 'In codominance, one allele completely masks the other, while in incomplete dominance, both alleles are fully expressed.' This is incorrect because in codominance, neither allele masks the other; both are fully expressed. In incomplete dominance, the phenotype is a blend, not full expression of both alleles.