To cause cancer, tumor suppressor genes require allele(s) to be mutated and therefore are considered The mutation results in a of function.
The Correct Answer and Explanation is:
Correct Answer:
To cause cancer, tumor suppressor genes require both alleles to be mutated and therefore are considered recessive. The mutation results in a loss of function.
Explanation (300+ words):
Tumor suppressor genes are critical regulators of the cell cycle, DNA repair, and apoptosis (programmed cell death). Their primary role is to prevent uncontrolled cell growth and tumor development. Examples include TP53, RB1, BRCA1, and BRCA2. For these genes to lose their ability to control cell division and thus contribute to cancer development, both copies (alleles) must be inactivated. This is known as the “two-hit hypothesis”, a concept proposed by Alfred Knudson based on studies of retinoblastoma.
In a normal cell, one functioning allele of a tumor suppressor gene is usually sufficient to maintain normal cell regulation. Therefore, these genes are considered recessive at the cellular level—meaning both alleles need to be mutated or inactivated for their protective function to be lost. If only one allele is mutated, the other can often compensate. However, when the second allele is also lost or mutated (the “second hit”), the protective effects are eliminated, potentially allowing the cell to divide uncontrollably.
The type of mutation involved in tumor suppressor genes is typically a “loss of function” mutation. This means the gene product (usually a protein) either is not made or does not work correctly. Such mutations can result from deletions, nonsense mutations, frameshift mutations, or epigenetic changes like promoter methylation that silence gene expression.
This mechanism is in contrast to proto-oncogenes, which typically require only one allele to be mutated and function in a dominant, gain-of-function manner to promote cancer.
In summary, for cancer to arise due to tumor suppressor gene inactivation, both alleles usually need to be mutated or lost, resulting in a loss of function. This dual inactivation removes a critical layer of growth control, facilitating unregulated proliferation and tumor development.