Which of the following is correct

Options

A. Haemophilic -Y chromosome
B. Down's syndrome -21 st chromosome
C. Sickle cell anamia -X chromsome
D. Parkinson's disease -X and Y chromosomes.

Answer

To solve the question "Which of the following is correct?" regarding genetic disorders and their chromosomal associations, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Hemophilia**:
- Hemophilia is a genetic disorder that affects the blood's ability to clot.
- It is caused by mutations in genes responsible for producing clotting factors.
- **Key Point**: The gene for hemophilia is located on the **X chromosome**, not the Y chromosome.
- **Conclusion**: The statement that hemophilia occurs on the Y chromosome is **incorrect**.

2. **Understanding Down Syndrome**:
- Down syndrome, also known as trisomy 21, occurs when there is an extra copy of chromosome 21.
- This condition is characterized by distinct physical features and developmental delays.
- **Key Point**: Down syndrome is indeed associated with the **21st chromosome**.
- **Conclusion**: The statement that Down syndrome occurs on the 21st chromosome is **correct**.

3. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is caused by a mutation in the hemoglobin beta gene.
- This mutation leads to the production of abnormal hemoglobin, affecting red blood cell shape and function.
- **Key Point**: The gene for sickle cell anemia is located on **chromosome 11**, not on the X chromosome.
- **Conclusion**: The statement that sickle cell anemia occurs on the X chromosome is **incorrect**.

4. **Understanding Parkinson's Disease**:
- Parkinson's disease is a progressive neurological disorder that affects movement.
- It is associated with degeneration of specific brain regions, particularly the substantia nigra.
- **Key Point**: While there may be genetic factors linked to Parkinson's disease, it is not specifically associated with the X or Y chromosomes in a definitive manner.
- **Conclusion**: The statement that Parkinson's disease occurs on the X and Y chromosomes is **incorrect**.

### Final Conclusion:
After analyzing all the options, the only correct statement is regarding **Down syndrome**, which is associated with the **21st chromosome**.