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Name ________________________ Lakeland High School Date _________________________ Biology/Ms. Tsai Mitosis Background – All cells have DNA – What is DNA? Our “blueprints” The instructions for who and what we are DNA is packaged into chromosomes Every species has a unique number of chromosomes Humans ______46____ Cat _____ 38_____ Pig ___ 38_____ Goat ___ 60_____ Dog ____ 78_____ Important: Chromosomes is specific for each species, and must be maintained for the species to continue Life of a cell All living things have a life cycle, even cells. Each cell has a beginning, a period of growth, and then an ending. The first phase of the life cycle of a cell is interphase During interphase, 2 things happen: 1. cell grows 2. chromosomes double----they each make an exact copy of itself After interphase comes mitosis During mitosis, cells divide to produce 2 exact copies of itself, resulting in one parent cell becoming two daughter cells Error! Purposes of mitosis In one-celled organisms: It is the way they reproduce - one organism becomes two Key to remember is that all offspring produces this way are all the same –no variation In many celled organisms: 1. Repair and replacement 2. Growth and development Mitosis – step by step Before mitosis (cell division) actually begins, there is interphase Cell grows: And chromosomes replicate: (make a copy) So at the end of interphase, the cell looks like this: Now mitosis begins: There are 4 stages of mitosis: Prophase, Metaphase, Anaphase and Telophase So, remember PMAT to remember them in order: Prophase: Nuclear membrane breaks down Centriole move apart from each other & a spindle starts to form between them Metaphase: Centrioles are at opposite ends of the cell Chromsomes are lined up in the middle of the cell Anaphase The spindle fibers pull the chromosomes apart; each set is pulled toward the opposite end of the cell Telophase Cell begins to “pinch in” The nuclear membranes reform around the chromosomes, 1 at each end of the cell Cytokinesis The cell now splits completely into 2 cells We now have two cells, each identical to the original parent cell and to each other! Summary Questions 1. What can we say about the daughter cells in mitosis compared to the parent cell? 2. What is the purpose of mitosis in unicellular organisms? 3. Name two ways in which mitosis is used in multicellular organisms 1. 2. 4. What is the phase of the cell cycle called where the cell is growing and the chromosomes replicate? 5. In which stage of mitosis do the chromatids line up at the middle? 6. What would most likely result if mitosis was not followed by division of the cytoplasm at the end (cytokinesis)?