Final answer:
The rare situation where only one of the two copies of a tumor-suppressor gene needs to be inactivated before there is a progression toward cancer is called dominant negative effect.
Step-by-step explanation:
The rare situation where only one of the two copies of a tumor-suppressor gene needs to be inactivated before there is a progression toward cancer is called dominant negative effect.
Normally, tumor suppressor genes act as a brake pedal in the cell's cycle, preventing uncontrolled division. However, in some cases, one mutated allele of a tumor suppressor gene can render the other copy non-functional, leading to unwanted cell division and cancer progression.