Mark the correct statement (w.r.t. sickle cell -anaemia)

Options

A. Homozygous individuals for `Hb^(S)` are apparently unaffected
B. Heterozygous individuals exhibits sickle-cell trait
C. Heterozygous individuals are affected as well as carrier
D. Homozygous individuals for `Hb^(A)` show the diseased phenotype

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder that affects the shape and function of red blood cells. In this condition, red blood cells become rigid and shaped like a sickle or crescent, which impairs their ability to carry oxygen effectively.

2. **Genetic Basis**:
- Sickle cell anemia is inherited in an autosomal recessive pattern. This means that an individual must inherit two copies of the mutated gene (one from each parent) to exhibit the disease.

3. **Homozygous vs. Heterozygous Individuals**:
- **Homozygous Individuals (HbSS)**: These individuals have two copies of the sickle cell allele (HBS). They are affected by sickle cell anemia and exhibit the disease phenotype.
- **Heterozygous Individuals (HbAS)**: These individuals carry one normal allele (HbA) and one sickle cell allele (HBS). They are typically asymptomatic and are referred to as carriers. They may exhibit a sickle cell trait but do not suffer from the disease itself.

4. **Evaluating the Statements**:
- **Statement 1**: "Homozygous individual for HBS are apparently unaffected."
- This statement is **incorrect** because homozygous individuals (HbSS) are affected by sickle cell anemia.
- **Statement 2**: "Heterozygous individual exhibit sickle cell trait."
- This statement is **correct**. Heterozygous individuals (HbAS) do exhibit the sickle cell trait but are not affected by the disease.
- **Statement 3**: "Heterozygous individuals are affected as well as the carrier."
- This statement is **incorrect**. Heterozygous individuals are carriers and are not affected by the disease.
- **Statement 4**: "Homozygous individual for HbA show the disease phenotype."
- This statement is **incorrect**. Homozygous individuals for HbA (HbAA) do not have sickle cell anemia.

5. **Conclusion**:
- The correct statement regarding sickle cell anemia is: "Heterozygous individual exhibit sickle cell trait."