Assertion : Sickle-cell anaemia is an autosome-linked recessive disorder that can be transmitted if both parents are heterozygous for the gene
Reason : In sickle-cell anaemia, haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in shape in RBC

Answer

To solve the question regarding the assertion and reason about sickle-cell anaemia, we will go through the following steps:

### Step 1: Understand the Assertion
The assertion states that "Sickle-cell anaemia is an autosome-linked recessive disorder that can be transmitted if both parents are heterozygous for the gene."
- **Explanation**: Sickle-cell anaemia is indeed an autosomal recessive disorder. This means that an individual must inherit two copies of the sickle-cell gene (one from each parent) to express the disease. If both parents are heterozygous (carriers), there is a 25% chance that their child will inherit both recessive alleles and thus have sickle-cell anaemia.

### Step 2: Understand the Reason
The reason states that "In sickle-cell anaemia, the haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in shape in RBC."
- **Explanation**: In sickle-cell anaemia, the normal hemoglobin (HbA) is replaced by an abnormal form (HbS) due to a mutation. Under low oxygen conditions, HbS molecules aggregate or polymerize, leading to the distortion of red blood cells (RBCs) from their normal biconcave shape to a sickle shape.

### Step 3: Analyze the Relationship Between Assertion and Reason
- Both the assertion and reason are true statements.
- However, the reason does not correctly explain the assertion. While the reason describes the mechanism of how sickle-cell anaemia affects red blood cells, it does not explain why the disorder is inherited in a recessive manner or how it can be transmitted if both parents are heterozygous.

### Step 4: Conclusion
Based on the analysis:
- The assertion is true.
- The reason is true, but it does not provide the correct explanation for the assertion.

Thus, the correct answer is that both statements are true, but the reason is not the correct explanation for the assertion.

### Final Answer
**Both the assertion and reason are true, but the reason is not the correct explanation for the assertion.**

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