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: ABO blood group → classic example of co-dominance (IA + IB → AB).

Answer 1

The Correct Option is A

Step 1: Define co-dominance.
Co-dominance occurs when two alleles in a heterozygote are both expressed fully and equally without blending.
Step 2: Classic example.
The best example is the ABO blood group system in humans, where IA and IB alleles are co-dominant, producing AB blood group.
Step 3: Check options.
- Co-dominance: Correct, both alleles are expressed.
- Partial dominance: Wrong, here heterozygote shows intermediate phenotype.
- Pseudo dominance: Wrong, occurs when recessive allele is expressed due to deletion of dominant allele.
- Over dominance: Wrong, heterozygote expresses a trait stronger than either homozygote.
Step 4: Conclusion.
Hence, when both alleles of a gene are fully expressed in heterozygotes, it is called Co-dominance.