Most common abnormality of proto-oncogene in human tumours is
**Core Concept**
The proto-oncogenes are normal genes that have the potential to become oncogenes, leading to cancer when mutated or overexpressed. They play a crucial role in regulating cell growth, division, and differentiation.
**Why the Correct Answer is Right**
The most common abnormality of proto-oncogenes in human tumors is point mutations, which result in the activation of these genes. This can be caused by genetic alterations such as amplification, translocation, or point mutations that lead to the overexpression or constitutive activation of the proto-oncogene product. For example, the BCR-ABL fusion gene resulting from a translocation between chromosomes 9 and 22 is a well-known example of a proto-oncogene activation in chronic myeloid leukemia. The activation of proto-oncogenes can lead to uncontrolled cell growth, a hallmark of cancer.
**Why Each Wrong Option is Incorrect**
* **Option A:** Gene deletion is a common abnormality in tumor suppressor genes, not proto-oncogenes.
* **Option B:** Chromosomal instability is a hallmark of cancer, but it is not the most common abnormality of proto-oncogenes.
* **Option D:** Epigenetic silencing is a mechanism of tumor suppressor gene inactivation, not a common abnormality of proto-oncogenes.
**Clinical Pearl / High-Yield Fact**
The activation of proto-oncogenes is a key event in the development of many types of cancer, and understanding the molecular mechanisms underlying this process is crucial for the development of targeted therapies.
**Correct Answer: A. Point mutations.**