Using the brake pedal analogy, explain the impact on the cell cycle of one mutated tumor suppressor gene allele versus two mutated tumor suppressor gene alleles.

Tumor suppressor genes typically inhibit division of cancer cells and preventing tumor formation. Mutation in this gene result in loss of function so it is typically recessive. This means that tumor suppressor genes acts as brake in formation of cancer cell. It prevents the growth of tumors. If one brake (one tumor suppressor gene) is defective it can still stop the car or cancer formation. However, since mutation in tumor suppressor gene is recessive, if two brakes are defective the car will not stop. Or the tumor will be expressed and be formed.