Select an incorrectly matched pair.

Options

A. Down's syndrome-Trisomy
B. Turner's syndrome- Lack of secondary sexual charcters.
C. Down's syndrome-Partially open mouth
D. Klinefelter's syndrome- Additional copy of X-chromosome due to duplication

Answer

To solve the question of selecting an incorrectly matched pair, let's analyze each option step by step:

1. **Down syndrome - Trisomy**:
- Down syndrome is indeed caused by trisomy of chromosome 21, which means there is an extra copy of this chromosome. This statement is correctly matched.

2. **Turner syndrome - Lack of secondary sexual characters**:
- Turner syndrome occurs in females and is characterized by the absence of one X chromosome (45,X). This condition leads to the lack of secondary sexual characteristics, making this statement also correctly matched.

3. **Down syndrome - Partially open mouth**:
- Individuals with Down syndrome often have a characteristic appearance that includes a partially open mouth due to a protruding tongue. This statement is correctly matched.

4. **Klinefelter syndrome - Additional copy of X chromosome due to duplication**:
- Klinefelter syndrome is a condition in males where there is an extra X chromosome (typically 47,XXY). However, this extra chromosome is due to nondisjunction during meiosis, not simply "duplication." Therefore, this statement is incorrectly matched.

Based on the analysis above, the incorrectly matched pair is:

**Klinefelter syndrome - Additional copy of X chromosome due to duplication.**