Absence of one sex-chromosome causes:

Options

A. Turner's syndrome
B. Klinefelter's syndrome
C. Down's syndrome
D. Haemophilia

Answer

### Step-by-Step Solution:

1. **Understanding Sex Chromosomes**:
- Humans typically have two sex chromosomes: XX for females and XY for males. The absence of one sex chromosome can lead to specific genetic disorders.

2. **Identifying the Condition**:
- The question asks about the absence of one sex chromosome. This condition is specifically known as Turner syndrome.

3. **Genotype of Turner Syndrome**:
- The genotype associated with Turner syndrome is 45, X0 (or 44 + X0), indicating that there is only one X chromosome present in an otherwise typical set of chromosomes.

4. **Other Options**:
- Klein Filter syndrome (Klinefelter syndrome) involves the presence of an extra X chromosome (XXY).
- Down syndrome is caused by an extra copy of chromosome 21 (trisomy 21) and is not related to sex chromosomes.
- Hemophilia is a genetic disorder related to blood clotting, typically linked to mutations on the X chromosome but does not involve the absence of a sex chromosome.

5. **Conclusion**:
- Therefore, the absence of one sex chromosome specifically causes Turner syndrome.

### Final Answer:
The absence of one sex chromosome causes Turner syndrome.