Examine the flow chart above depicting the job of a gene known as p53. It plays an important role during the G2 checkpoint of cell cycle regulation. In 4-6 sentences, explain why p53 is often called "The Guardian of the Genome". Is p53 an oncogene (a gene that stimulates the growth of cancer cells) or a tumor suppressor gene (a gene that turns off the growth of cancer cells)? Explain your reasoning.