The cell cycle is a term used to describe the entire process of one individual cell replicating itself. All of the DNA within the cell is copied, segregated and replicated; forming two genetically identical daughter cells. It is referred to as a cycle rather than a linear path as at the end of the process, the two daughter cells produced can immediately begin the next cycle. In eukaryotes (cells with nuclei) there are two key periods: the interphase and the mitotic phase. The interphase consists of a cell growth period (G1), followed by DNA replication (S phase) then a secondary growth period (G2). During the interphase, the cell undertakes regular functions whilst growing and replicating some of its organelles, preparing to split into two fully functioning daughter cells. During DNA replication, all chromosomes within the nucleus unwind and the DNA is copied. The miotic phase is when mitosis occurs and two new nuclei are formed, immediately following this, cytokinesis splits the cell into two daughter cells. Mistakes within the cell cycle can be damaging, hence the process of cell division and the cell cycle is heavily regulated. Errors within the cell cycle can cause a variety of diseases, such as cardiovascular and neurodegenerative diseases, and cancer.