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 of the given statements regarding genetic disorders and determine their accuracy.

### Step-by-Step Solution:

1. **Analyze Hemophilia**:
- Hemophilia is described as a bleeder's disease caused by a defective mechanism of blood clotting.
- It is stated to be a sex-linked recessive disorder.
- **Conclusion**: This statement is correct. Hemophilia is indeed a sex-linked recessive disorder associated with the X chromosome.

2. **Analyze Cystic Fibrosis**:
- The statement claims that cystic fibrosis is an autosomal dominant disorder.
- However, cystic fibrosis is known to be an autosomal recessive disorder.
- **Conclusion**: This statement is incorrect. Cystic fibrosis is not autosomal dominant; it is autosomal recessive.

3. **Analyze Down Syndrome**:
- Down syndrome is described as a trisomy of the 21st chromosome.
- It is noted that this condition arises from a defective egg fertilized by a normal sperm, leading to an extra copy of chromosome 21.
- **Conclusion**: This statement is correct. Down syndrome is indeed a trisomy of the 21st chromosome (47 chromosomes total).

4. **Analyze Turner's Syndrome**:
- Turner's syndrome is described as a monosomy of the X chromosome, represented as 2n-1, with a total of 45 chromosomes (X0).
- It is characterized by various physical and developmental features.
- **Conclusion**: This statement is correct. Turner's syndrome is a monosomy of the X chromosome.

### Final Conclusion:
The only mismatched statement is regarding cystic fibrosis, which is incorrectly labeled as an autosomal dominant disorder when it should be classified as an autosomal recessive disorder. Therefore, the answer is:

**Mismatched Pair: Cystic Fibrosis (Option 2)**

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