Final answer:
The reference material does not provide information on the percentage of tumors that need Z DNA to survive, but it does explain that over 50 percent of human tumors have mutated p53 genes, which affects the cell's ability to repair DNA and prevent tumor growth.
Step-by-step explanation:
The question about the percentage of tumors that need Z DNA to survive is not specifically answered in the provided reference material. However, there is detailed information about the role of mutations in the p53 gene in tumor cells. Mutated p53 genes have been identified in more than 50 percent of all human tumor cells, which is critical considering the multiple roles that the p53 protein plays at the G₁ checkpoint in the cell cycle. The p53 protein activates other genes whose products halt the cell cycle, participate in DNA repair, or initiate cell death when DNA damage cannot be repaired. If the p53 protein is damaged, it may fail to halt the cell cycle or to initiate DNA repair, allowing cells with damaged DNA to continue dividing and potentially leading to cancer.