Tumor Suppressor Genes and Cancer Risk

Steps:

• BRCA1 protein normally inhibits breast cancer cell growth; p53 suppresses tumors.
• Mutations inactivate these tumor suppressors, allowing uncontrolled cell proliferation.
• Breast cancer requires loss of function in both genes for high risk.
• Option A shows both genes as inactive (x = mutated/inactive).

Why A is correct:

• Per the two-hit hypothesis, biallelic inactivation of tumor suppressors like BRCA1 and p53 removes growth controls, directly causing cancer predisposition.

Why the others are wrong:

• B: One normal gene retains partial suppression, reducing cancer likelihood.
• C: Normal genes fully inhibit growth and tumors, preventing cancer.
• D: Mutated label unclear, but implies active function, not leading to cancer.

Final answer: A