Which of the following occurs due to monosomy of chromosomes ?

Options

A. Turner syndrome
B. haemophillia
C. Phenyl ketonuira
D. Sickle cell anaemia

Answer

### Step-by-Step Solution:

1. **Understanding Monosomy**:
- Monosomy refers to the condition where there is a missing chromosome in a pair. In humans, this means having only one chromosome instead of the normal two (2n - 1).

2. **Identifying the Options**:
- The options given are:
- A) Turner's syndrome
- B) Hemophilia
- C) Phenylketonuria
- D) Sickle cell anemia

3. **Analyzing Each Condition**:
- **Turner's Syndrome**: This condition is characterized by the absence of one X chromosome in females, resulting in a genotype of XO. It is indeed a result of monosomy (specifically, monosomy of the X chromosome).
- **Hemophilia**: This is a genetic disorder that affects blood clotting but is not caused by monosomy. It is typically linked to mutations in genes on the X chromosome.
- **Phenylketonuria (PKU)**: This is a metabolic disorder caused by a deficiency in the enzyme phenylalanine hydroxylase, not related to monosomy.
- **Sickle Cell Anemia**: This is a genetic disorder caused by a mutation in the hemoglobin gene, leading to abnormally shaped red blood cells. It is not related to monosomy.

4. **Conclusion**:
- Based on the analysis, the only condition that occurs due to monosomy of chromosomes is **Turner's syndrome**.

### Final Answer:
The correct option is **Turner's syndrome**.

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