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Mitosis and the Cell Cycle The Cell Cycle Why Do Cells Divide? Reproduction (for single celled organism) Growth Repair and Replacement (for multicellular organisms) Interphase (longest part of the cell cycle) G0 (Cell is at rest not preparing to divide) G1 (Growth 1) S (Synthesis) - copies DNA so that both the old and new cells have identical chromosomes G2 (Growth 2) - cell prepares for division Cell Division: Mitosis (M-phase) nuclear division followed by a cellular division, the number of chromosomes remains the same mitosis occurs in somatic cells which are any cells in the body except a gamete (sex cell) o chromosomes are in pairs in somatic cells, one chromosome of the pair was passed on by the mother and the other by the father mitosis does not produce sex cells (ex. sperm and egg) which have ½ the number of chromosomes as somatic cells Mitotic Phases Interphase (technically not part of mitosis, but it is included in the cell cycle) Cell is in a resting phase, performing normal cell functions DNA replicates and remains in uncondensed thread-like tangles called chromatin Organelles double in number, to prepare for division Prophase Spindle forms Centrioles move to opposite poles Chromosomes become visible as sister chromatids (replicated or doubled chromosomes), two chromosomes attached at a single point. Mitosis and the Cell Cycle Metaphase Chromosomes line up along the equator Anaphase Sister chromatids(replicated or doubled chromosomes) are separated Chromatids separate and move to opposite poles Telophase Nuclear membrane forms around each group of chromosomes Chromosomes unwind Cytokinesis begins o Cytokinesis is The process by which the cytoplasm divides and one cell becomes two individual cells