What is the cause of sickle-cell anaemia?

Explanation

### 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 (RBCs).

2. **Classification**:
- It is classified as a Mendelian disorder, specifically an autosomal recessive disorder. This means the gene responsible for the condition is located on an autosome (non-sex chromosome) and is recessive.

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