Turner syndrome is caused by

Options

A. autosomal Aneuploidy
B. sex chromosome aneuploidy
C. polyploidy
D. trisomy

Answer

**Step-by-Step Solution:**

1. **Understanding Turner Syndrome**: Turner syndrome is a genetic disorder that affects females and is characterized by the presence of only one X chromosome instead of the usual two (XX). This condition is often denoted as 45,X or X0.

2. **Chromosomal Composition**: Normally, humans have a total of 46 chromosomes, which include 44 autosomes and 2 sex chromosomes. In females, these sex chromosomes are typically XX, while males have XY.

3. **Cause of Turner Syndrome**: In Turner syndrome, there is a missing sex chromosome, specifically one of the X chromosomes. This absence leads to various developmental issues, including sterility and underdevelopment of secondary sexual characteristics.

4. **Identifying the Type of Aneuploidy**: The term "aneuploidy" refers to an abnormal number of chromosomes. In the case of Turner syndrome, it is a type of sex chromosome aneuploidy because it involves the loss of one of the sex chromosomes (the X chromosome).

5. **Evaluating the Options**:
- **Option A (Autosomal Aneuploidy)**: Incorrect, as Turner syndrome involves sex chromosomes, not autosomes.
- **Option B (Sex Chromosome Aneuploidy)**: Correct, as it specifically refers to the missing X chromosome in Turner syndrome.
- **Option C (Polyploidy)**: Incorrect, as polyploidy involves the addition of complete sets of chromosomes, not the loss of one.
- **Option D (Trisomy)**: Incorrect, as trisomy refers to the presence of an extra chromosome, which is not the case in Turner syndrome.

6. **Conclusion**: The correct answer is **Option B: Sex Chromosome Aneuploidy**, as Turner syndrome is caused by the absence of one X chromosome.

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