Questions: All of the following are true of the Rb gene, EXCEPT: Rb mutation of one allele causes retinoblastoma. Rb normally inhibits growth. Rb mutation is common to many types of cancer. Rb is a tumor suppressor which inhibits trascription activity.

The answer is the first one: Rb mutation of one allele causes retinoblastoma.

Explanation for each option:

1. Rb mutation of one allele causes retinoblastoma.

   • This statement is incorrect. Retinoblastoma typically requires mutations in both alleles of the Rb gene for the cancer to develop. The Rb gene follows the "two-hit hypothesis," where both copies of the gene must be inactivated for tumor formation.

2. Rb normally inhibits growth.

   • This statement is correct. The Rb protein is a tumor suppressor that regulates the cell cycle by inhibiting cell growth and proliferation.

3. Rb mutation is common to many types of cancer.

   • This statement is correct. Mutations in the Rb gene are associated with various types of cancer, not just retinoblastoma.

4. Rb is a tumor suppressor which inhibits transcription activity.

   • This statement is correct. The Rb protein functions as a tumor suppressor by inhibiting transcription factors that promote cell cycle progression.

In summary, the incorrect statement is that a mutation of one allele of the Rb gene causes retinoblastoma, as both alleles typically need to be mutated for the disease to manifest.