Tumour suppressor genes regulate the cell cycle and DNA replication. These prevent uncontrollable divisions from happening. For example, the p53 gene detects DNA damage and induces cell cycle arrest or apoptosis to prevent mutated cells from replicating. If the p53 gene is mutated, this results in the loss of DNA damage detection, potentially enabling mutated cells to replicate and divide uncontrollably. This could lead to tumour development and cells growing cancerous.