How Can a Mutation in a Tumor-Suppressor Gene Behave as a Recessive

Multiple Choice

How can a mutation in a tumor-suppressor gene behave as a recessive allele at the cellular level, but appear as a dominant allele in pedigree analysis?

A) Some functional protein can still be produced in a cell heterozygous for a loss-of-function allele; however, an additional mutation can inactivate the second allele, eliminating all functional protein allowing cancer to occur in many family members.
B) A single functional allele is sufficient to regulate the cell cycle, but not sufficient to promote apoptosis, allowing cancer to develop in every generation.
C) A cell with half the amount of the functional tumor-suppressor protein can form benign tumors that will occur in every generation in the pedigree.
D) Some functional protein can still be produced in a cell heterozygous for a loss-of-function allele; but loss-of-function tumor-suppressor alleles are so common in the population that many individuals are homozygous.