Find out the MISMATCHED pair.

Options

A. Haemophilia - Sex linked recessive
B. Cystic fibrosis - Autosomal dominant
C. Down's syndrome - Trisomy 21
D. Turner's syndrome - X-linked

Answer

To solve the question of finding the mismatched pair, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the first option: Hemophilia and sex-linked recessive**
- **Analysis**: Hemophilia is indeed a sex-linked recessive disorder. It is caused by a mutation in a gene on the X chromosome. Therefore, this pair is correctly matched.

2. **Identify the second option: Cystic fibrosis and autosomal dominant**
- **Analysis**: Cystic fibrosis is actually an autosomal recessive disorder, not autosomal dominant. This means that the correct inheritance pattern for cystic fibrosis is that two copies of the mutated gene (one from each parent) are necessary for the disease to manifest. Thus, this pair is mismatched.

3. **Identify the third option: Down syndrome and trisomy 21**
- **Analysis**: Down syndrome is correctly matched with trisomy 21. It is characterized by the presence of an extra copy of chromosome 21, leading to developmental and intellectual delays. Therefore, this pair is correctly matched.

4. **Identify the fourth option: Turner syndrome and X-linked**
- **Analysis**: Turner syndrome is a chromosomal disorder that occurs in females who have only one X chromosome (45,X). It is not classified as X-linked; rather, it is a result of a chromosomal anomaly. However, this pair is also correctly matched in the context of chromosomal disorders.

### Conclusion:
The mismatched pair is **Cystic fibrosis and autosomal dominant** (Option 2).