17. The mutation in an oncogene falls under which of the following classes?
(1) Loss of function mutation
(2) Frame shift mutation
(3) Gain of function mutation
(4) Dominant negative mutation

Final Answer

The mutation in an oncogene falls under the class of:

(3) Gain of function mutation

Explanation

Oncogenes are mutated forms of normal cellular genes called proto-oncogenes. These mutations lead to a gain of function—meaning the gene product’s activity is increased or constitutively active, promoting uncontrolled cell proliferation and survival.​

These activating mutations can include:

• Point mutations or base substitutions that alter a single amino acid, leading to a hyperactive protein (common in the ras oncogene).

• Gene amplifications that increase the number of copies of the proto-oncogene, resulting in overexpression.

• Chromosomal translocations that place the proto-oncogene under a strong promoter or fuse it with another gene, producing chimeric proteins with novel oncogenic activity.

These gain of function mutations turn a regulated proto-oncogene into an oncogene driving cancer progression.

Other options explained:

• Loss of function mutation (Option 1) typically applies to tumor suppressor genes, not oncogenes.

• Frame shift mutation (Option 2) can occur but is not the defining mutation type for oncogenes; it often results in loss of function.

• Dominant negative mutation (Option 4) usually refers to mutant proteins that antagonize the function of the wild-type protein, more relevant to tumor suppressors.