B2 5.1-5.2 Mitosis and Meiosis

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  • Cell Division
    • Mitosis
      • Replaces damaged cells
      • Allows all living organisms to grow
      • Allows organisms to replicate whole copies of themselves
      • Supplies new cells quickly and correctly
      • The cell that is going to divide must double its contents
        • Replicates chromosomes and organelles like mitochondria and ribosomes
        • The cell ends up with 46 pairs of chromosomes
          • Divides into two new cells
            • Daughter cells
              • 23 pairs of chromosomes (two sets)
              • Carry the same genetic information as the parent cells
      • Can be used by some plants to reproduce asexually
      • One division
      • Results in two identical cells
    • Meiosis
      • Gametes are formed through this process
        • Gametes contain 23 chromosomes (a single set)
      • Takes place in the testes of a male
        • Sperm
      • Takes place in the ovaries of a female
        • Ova
      • Only involved in forming gametes
        • Varied offspring
      • Produces 4 different gametes
      • Doubles up chromosomes
        • Ensures there are enough -too many/too little the cell won't work properly (or even at all)
      • 1st division - a cell with 46 pairs of chromosomes splits into two - two cells each with 23 pairs
        • 2nd division - 2 cells both split, forming 4 daughter cells each with varying chromosomes
      • Cells are varied because it's totally random which chromosomes go into which cell
      • In fertilisation, the gamete fuses with a gamete of the opposite sex so that the new cell has 23 pairs of chromosomes
        • This cell then divides by mitosis

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