Final answer:
The Philadelphia chromosome is characterized by a translocation between chromosomes 9 and 22, creating the BCR-ABL fusion protein that is associated with chronic myelogenous leukemia.
Step-by-step explanation:
The chromosomal defect found in the Philadelphia chromosome is a translocation between chromosome 9 and chromosome 22. This occurs when a segment from one chromosome becomes detached and reattaches to a different chromosome, which can lead to the development of chronic myelogenous leukemia (CML). In the case of the Philadelphia chromosome, this translocation results in the fusion of the BCR gene from chromosome 22 and the ABL gene from chromosome 9, creating an oncogenic tyrosine kinase known as BCR-ABL.
This chromosomal rearrangement disrupts normal cell regulation and is implicated in the pathogenesis of CML. The BCR-ABL fusion protein created by this translocation exhibits constant tyrosine kinase activity, leading to uncontrolled cell division and the accumulation of malignant cells associated with this type of leukemia.
In summary, the correct answer to the student's question is D Translocation.