Cell Division

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  • Cell Division
    • Mitosis
      • Body cells have two copies of each chromosome- one from the mother and one from the father
      • 23 pairs of chromosomes in a human cell
      • Used for growth, cell repair and replacement
      • It is when a cell reproduces itself by splitting to form two identical offspring
      • Stage 1- In a cell that's not dividing the DNA is spread out in long strings
      • Stage 2- if a cell gets the signal to divide, it duplicates its DNA (each arm is an exact duplicate of the other)
      • Stage 3- chromosomes then line up in the cantre of the cell and the cell fibres pull them apart
      • Stage 4- membranes form around each set of chromosomes- nuclei of the two new cells and the cytoplasm divides
      • Stage 5- now have two new cells containing exactly the same DNA- they're identical
      • Asexual Reproduction- no variation
    • Meiosis
      • Sexual Reproduction- variation (mixture of two sets of chromosomes)
      • Gametes- one copy of each chromosome, one sex cell from mother and one sex cell from father
      • Gametes have 23 chromosomes each, so when they combine you get 46 (23 pairs- human cell)
        • Sexual Reproduction- variation (mixture of two sets of chromosomes)
      • It produces cells which have half the normal number of chromosomes
      • Stage 1- duplicates its DNA- one arm of each chromsome is an exact copy of the other arm
      • Stage 2- first division, chromosomes line up in the centre of the cell
      • Stage 3- pairs are then pulled apart, so each new cell only has one copy of each chromosome- some of mothers and some of fathers
      • Stage 4- second division- chromsomes line up and the arms are pulled apart
      • Stage 5- four gametes each with a single set of chromosmes


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