`Hb^(A) and Hb^(S)` alleles of normal and sickle cell haemoblobin are

Options

A. codominant alleles
B. multiple alleles
C. polygenic alleles
D. cumulative alleles

Explanation

To answer the question about the Hb^(A) and Hb^(S) alleles of normal and sickle cell hemoglobin, we can break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Alleles**:
- Hb^(A) represents the normal hemoglobin allele.
- Hb^(S) represents the sickle cell hemoglobin allele.

2. **Inheritance Pattern**:
- Sickle cell anemia is an autosomal recessive disorder. This means that an individual must inherit two copies of the Hb^(S) allele (Hb^(S)/Hb^(S)) to express the disease.

3. **Genotypes**:
- There are three possible genotypes concerning these alleles:
- Homozygous normal: Hb^(A)/Hb^(A)
- Heterozygous (sickle trait): Hb^(A)/Hb^(S)
- Homozygous sickle cell: Hb^(S)/Hb^(S)

4. **Expression of Traits**:
- The homozygous condition (Hb^(S)/Hb^(S)) leads to sickle cell disease.
- The heterozygous condition (Hb^(A)/Hb^(S)) leads to what is known as the sickle cell trait. Individuals with this genotype do not typically show symptoms of the disease but can pass the Hb^(S) allele to their offspring.

5. **Co-dominance**:
- In the heterozygous state (Hb^(A)/Hb^(S)), both alleles are expressed. This means that both normal and sickle hemoglobin are produced. This phenomenon is referred to as co-dominance, where both alleles contribute to the phenotype.

6. **Conclusion**:
- Therefore, the correct characterization of Hb^(A) and Hb^(S) alleles is that they are co-dominant alleles.

### Final Answer:
The Hb^(A) and Hb^(S) alleles of normal and sickle cell hemoglobin are co-dominant alleles.