During inter-phase of cell division, the genetic material is duplicated to allow for division into 2 identical daughter cells. The tumour suppressor gene checks for errors in the DNA, and if found, apoptosis (cell death) is initiated by p53 protein. The pRb (retinoblastoma) protein stops the progression of the cell cycle form G0 into S phase if the cell division is complete hence stemming unregulated cell division.