In case of chronic myetogenous lukemia, which one of the following is called "Philadelphia chromosome"?

Options

A. Chromosome 22
B. Chromosome 21
C. Chromosome 9
D. Chromosome 5

Answer

**Step-by-Step Solution:**

1. **Understanding Chronic Myelogenous Leukemia (CML)**:
- CML is a type of cancer that affects the blood and bone marrow. It is characterized by the overproduction of myeloid cells.

2. **Identifying the Philadelphia Chromosome**:
- The Philadelphia chromosome is a specific genetic abnormality associated with CML. It is formed due to a chromosomal translocation.

3. **Chromosomal Translocation**:
- In CML, there is a break and exchange of genetic material between chromosome 9 and chromosome 22. This process is known as translocation.

4. **Formation of the Philadelphia Chromosome**:
- During this translocation, a part of chromosome 9 is exchanged with a part of chromosome 22. The resulting chromosome (Philadelphia chromosome) primarily consists of chromosome 22 with a small portion of chromosome 9.

5. **Composition of the Philadelphia Chromosome**:
- The Philadelphia chromosome is predominantly made up of chromosome 22 (approximately 75%) and a smaller segment from chromosome 9 (approximately 25%).

6. **Conclusion**:
- Therefore, in the context of chronic myelogenous leukemia, the chromosome referred to as the "Philadelphia chromosome" is chromosome number 22.

**Final Answer**: The Philadelphia chromosome is chromosome number 22.

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