Why are tumor suppressors usually recessive? a. because by definition a mutant protein is always recessive to a wild-type protein b. because a loss of function mutation of only one allele usually has no effect on the phenotype c. because the fusion studies showed that wild type tumor suppressors were recessive to activated oncogenes d. because pro-proliferative signaling is always dominant over anti-proliferative signaling. e. all of the above are correct

The correct answer is option b. "Because a loss of function mutation of only one allele usually has no effect on the phenotype".

Explanation:

A recessive allele, does not have an effect in a phenotype if a dominant allele is present, it should be present in the two alleles in order to be expressed in the phenotype. A loss of function mutation of only one allele usually has no effect on the phenotype. This is the case for most tumor suppressors, which unfortunately most of them are recessive while mutant oncogene alleles are typically dominant.