Question

When both the alleles of a gene are fully expressed in the heterozygotes, it leads to which of the following?

• A. Co-dominance
• B. Partial Dominance
• C. Pseudo dominance
• D. Over-dominance

Hint:

Remember: Co-dominance = both alleles expressed fully (e.g., Roan coat color in cattle); Incomplete dominance = intermediate phenotype blended (e.g., pink flowers).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Gene action can exhibit different types of dominance depending on how alleles interact and express themselves in heterozygous individuals.

Step 3: Detailed Explanation:
Let us review the options provided:

• Co-dominance: Both alleles of a gene are fully and independently expressed in the heterozygote. A classic example is the AB blood group in humans, where both A and B antigens are fully expressed.

• Partial Dominance (Incomplete Dominance): The heterozygote phenotype is intermediate between the two homozygotes (e.g., pink flowers in Mirabilis jalapa).

• Pseudo-dominance: The temporary expression of a recessive allele due to the deletion of the dominant allele on the homologous chromosome.

• Over-dominance: The phenotype of the heterozygote is more extreme or superior to either of the homozygotes (e.g., sickle cell trait providing malaria resistance).

Step 4: Final Answer
Full expression of both alleles in the heterozygote is called co-dominance.