Mammalian cells divide by undergoing a process called a cell cycle.
This results in two daughter cells arising from each dividing parent. The cell cycle of eukaryotes is much more complicated than that of prokaryotes. In prokaryotes DNA is continuously synthesized and cells divide correspondingly under favorable conditions. In mammalian cells the division cycle contains only a discrete period of DNA synthesis, called S phase. This is flanked by two periods which antecede S phase or follow S phase and antecede mitosis when cells divide at the end of the cell cycle.