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:
Tumor suppressor genes are crucial components of our genome that help regulate the cell cycle, repair DNA damage, and ensure that cells with severe mutations undergo apoptosis (programmed cell death). Their primary role is to prevent the formation and growth of tumors.
A key characteristic of tumor suppressor genes is that both alleles (copies) must be inactivated for a loss of function to significantly contribute to cancer development. This concept is based on the “two-hit hypothesis”, first proposed by Alfred Knudson. According to this hypothesis, a person may inherit one mutated allele (the first “hit”) and then acquire a second mutation in the other allele later in life (the second “hit”), leading to complete loss of function of the tumor suppressor gene.
This is why mutations in tumor suppressor genes are considered recessive at the cellular level—both gene copies must be mutated or deleted for the protective function to be lost. This contrasts with oncogenes, which are typically dominant—a mutation in just one allele can promote uncontrolled cell division.
When a tumor suppressor gene is inactivated, the cell loses its ability to control growth, repair DNA damage, or trigger apoptosis. This loss of function enables the cell to survive and proliferate despite harboring genetic damage, contributing to cancer progression.
Examples of tumor suppressor genes include:
- TP53: Often called the “guardian of the genome,” it plays a role in DNA repair and apoptosis.
- RB1: Regulates the cell cycle by preventing the transition from G1 to S phase.
- BRCA1/BRCA2: Involved in DNA repair, especially in breast and ovarian tissue.
In summary, tumor suppressor gene mutations are recessive because both alleles must be inactivated, and these mutations cause a loss of function that removes vital controls over cell growth and survival, paving the way for cancer development.