Which of the following statements is correct 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 solve the question regarding sickle cell anemia, we need to analyze the statements provided and determine which one is correct. Here’s a step-by-step breakdown:

### Step 1: Understand Sickle Cell Anemia
Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. It is classified as an autosomal recessive disorder, meaning that two copies of the defective gene (HbS) must be present for the disease to manifest.

**Hint:** Remember that sickle cell anemia is an autosomal recessive disorder, which means it requires two copies of the mutated gene to express the disease.

### Step 2: Analyze the Statements
Now, let’s evaluate each statement provided in the question:

1. **Homozygous individuals for HbA show the diseased character.**
- This statement is incorrect. Homozygous individuals for HbA (normal hemoglobin) do not have sickle cell anemia.

**Hint:** Homozygous for HbA means both genes are normal; hence, they cannot show the disease.

2. **Heterozygous individuals are affected as well as carriers.**
- This statement is also incorrect. Heterozygous individuals (one normal gene and one defective gene) are carriers but do not exhibit the disease.

**Hint:** Heterozygous individuals carry the gene but do not show symptoms of the disease due to the recessive nature of the defective gene.

3. **Homozygous individuals for HbS remain unaffected.**
- This statement is incorrect. Homozygous individuals for HbS (two copies of the sickle cell gene) will be affected by sickle cell anemia.

**Hint:** If both genes are defective (HbS), the individual will express the disease.

4. **Homozygous individuals for HbS exhibit sickle cell trait.**
- This statement is correct. Individuals who are homozygous for HbS will have sickle cell anemia, which is characterized by the sickling of red blood cells.

**Hint:** The term "sickle cell trait" refers to individuals who are heterozygous (HbA/HbS), while homozygous individuals (HbS/HbS) exhibit the full disease.

### Step 3: Conclusion
After analyzing all the statements, the correct answer is that homozygous individuals for HbS exhibit sickle cell anemia.

**Final Answer:** The correct statement is: "Homozygous individuals for HbS exhibit sickle cell trait."