Loss of a tumor suppressor gene usually promotes cancer only if both copies are defective.
B You determine by immunoblotting that a tumor lacks a specific tumor suppressor protein. Then you sequence the regulatory and coding regions of the corresponding tumor suppressor gene and find that one copy has a premature stop codon near the beginning of the gene and the other copy contains no mutations. What is the most likely mechanism that prevents the production or accumulation of protein from the unmutated copy?