Final answer:
When a G1 cell sustains genetic damage, it may bypass the G1 checkpoint and proceed directly to S phase, resulting in daughter cells with accumulated mutations and potential tumor growth.
Step-by-step explanation:
When a G1 cell sustains genetic damage, its ability to proceed through the cell cycle is compromised. The G1 checkpoint, which determines if all conditions are favorable for cell division, is severely affected. Without a fully functional p53 gene, the cell may proceed directly from G1 to S phase, regardless of internal and external conditions. As a result, the cell can produce daughter cells with accumulated mutations, leading to tumor growth.