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 essential components of the cell’s regulatory mechanisms that prevent uncontrolled growth and division. They act as the “brakes” of the cell cycle, ensuring that damaged DNA is repaired, abnormal cells are destroyed (apoptosis), and that cell division only occurs when necessary. Examples include TP53, RB1, and BRCA1/BRCA2.
Unlike oncogenes—which can drive cancer with a mutation in only one allele (dominant)—tumor suppressor genes require mutations in both alleles (copies) to lose their function and contribute to cancer development. This is because the presence of even one functional allele is often sufficient to maintain the gene’s protective role. This concept is part of the “two-hit hypothesis,” first proposed by Dr. Alfred Knudson in 1971 while studying retinoblastoma, a rare childhood eye cancer.
Here’s how it works:
- The first hit is usually a germline (inherited) mutation or a spontaneous mutation in one allele of a tumor suppressor gene.
- The second hit often occurs later in life and affects the second, previously normal allele due to mutation, deletion, or epigenetic silencing.
Once both alleles are inactivated, the tumor suppressor gene can no longer perform its role in regulating cell growth or initiating apoptosis. This leads to uncontrolled cell proliferation, accumulation of DNA damage, and eventually, cancer.
Importantly, mutations in tumor suppressor genes are considered to cause a loss of function, meaning the protective role they usually play is eliminated. This is in contrast to oncogene mutations, which result in a gain of function—turning a normally regulated gene into one that promotes cancerous growth.
In summary, tumor suppressor genes are recessive at the cellular level, requiring both alleles to be mutated to cause cancer, and the mutation leads to a loss of function of the protective gene product