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Mitosis Somatic Cell Division Purpose • Reproduce asexual unicellular organisms • Bacteria • Archaeans • Protists • Replicate non-sexual/ somatic cells in multicellular organisms • Replace dead/ dying cells in tissues • Growth • Development When? When not? • If cells enter G0 phase • Full maturity (nerve cells) • Cells need to ‘rest’ • If cells do not pass the G1 checkpoint due to • Insufficient growth/ maturity • Inadequate resources in cell’s environment • If cells do not pass the G2 checkpoint due to • Improper replication of cell’s DNA during S phase • Insufficient growth of cell or amassment of cell parts • Lack of critical proteins, enzymes, or other signaling molecules Stages of Mitosis • Prophase • Chromosomes condense; nuclear envelope & nucleolus degrades; centrosomes migrate; spindle forms (kinetochore fibers vs. polar fibers) • Metaphase • Chromosomes migrate to middle of cell • Anaphase • Chromatids separate, moving toward opposite poles • Telophase • Chromosomes at opposite poles; nucleolus & nuclear envelope reassemble; spindle fibers disassemble; chromosomes chromatin