Which of the following statements is incorrect with respect to sickle cell anaemia?

Options

A. Homozygous individuals for HbA show the diseased character.
B. Heterozygous individuals are affected as well as carriers.
C. Homozygous individuals for HbS remain unaffected.
D. Homozygous individuals for HbS exhibit sickle cell trait.

Answer

To determine which statement is incorrect with respect to sickle cell anaemia, we need to analyze each option based on our understanding of the genetics involved in this condition.

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anaemia**:
- Sickle cell anaemia is caused by a mutation in the hemoglobin gene. The normal hemoglobin is referred to as HbA, while the mutated form is called HbS.
- Sickle cell anaemia is a recessive genetic disorder, meaning that an individual must inherit two copies of the HbS allele (HbS/HbS) to exhibit the disease.

2. **Analyzing the Statements**:
- **Statement 1**: "Homozygous individual for HbA shows the disease character."
- This statement is **correct**. Individuals who are homozygous for HbA (HbA/HbA) do not have sickle cell anaemia.

- **Statement 2**: "Heterozygous individuals are affected as well."
- This statement is **incorrect**. Heterozygous individuals (HbA/HbS) are carriers of the sickle cell trait but are generally not affected by the disease itself since the HbA allele is dominant over HbS.

- **Statement 3**: "Homozygous individuals for HbS remain unaffected."
- This statement is **incorrect**. Individuals who are homozygous for HbS (HbS/HbS) do exhibit sickle cell anaemia.

- **Statement 4**: "Homozygous individuals for HbS exhibit sickle cell trait."
- This statement is **correct**. Individuals who are homozygous for HbS (HbS/HbS) do exhibit sickle cell anaemia, which is a more severe form than the sickle cell trait seen in heterozygous individuals.

3. **Conclusion**:
- The incorrect statement is: "Heterozygous individuals are affected as well." This is because heterozygous individuals are carriers and do not exhibit the disease.

### Final Answer:
The incorrect statement with respect to sickle cell anaemia is: **"Heterozygous individuals are affected as well."**