Under what circumstances do we consider potentially cancer-causing mutations to be dominant?
The correct answer and explanation is:
Potentially cancer-causing mutations are considered dominant under certain circumstances when a single copy of the mutated gene is sufficient to increase the risk of cancer. These mutations typically affect proto-oncogenes or tumor suppressor genes, and their dominance depends on the specific type of mutation and how it alters cellular functions.
In the case of proto-oncogenes, a mutation that leads to a gain-of-function change can cause cancer in a dominant manner. Proto-oncogenes are normal genes that help regulate cell growth and division. When these genes are mutated, they can become oncogenes, which promote uncontrolled cell proliferation. A single copy of an oncogene is enough to drive this uncontrolled growth, making the mutation dominant. For example, mutations in the RAS gene, which is involved in cell signaling, can cause a cell to grow uncontrollably, even if only one copy of the gene is mutated.
On the other hand, mutations in tumor suppressor genes usually follow a recessive pattern in the context of cancer. These genes normally act as a brake on cell division, preventing the development of tumors. However, in cases where one mutated allele is inherited and the second allele is mutated during the course of a person’s life, cancer may develop. An example of this is the retinoblastoma gene (RB1), which requires both copies to be mutated for cancer to occur. However, if one mutated allele is inherited, the other allele can mutate later, making the mutation effectively dominant in driving cancer development.
Thus, cancer-causing mutations can be dominant when they occur in proto-oncogenes or when a mutation in a tumor suppressor gene is inherited, increasing the likelihood of a second mutation that leads to tumorigenesis.