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  • Mutations
    • Chromosome Mutations
      • involves random changes to the structure of a chromosome.
      • Inversion: a section of chromosome turns through 180 degrees.
      • Deletion: a part is lost.
      • Translocation: a piece of one chromosome becomes attached to another.
      • Non-disjunction: homologous chromosomes fail to separate properly at meiosis 1 or chromatids fail to separate at meiosis 2.
    • DNA Mutations
      • Changes to genes due to changes in nucleotide base sequences
      • Could happen when DNA is replicating before nuclear division by either mitosis or meiosis.
        • Mitosis: somatic mutations that aren't passed on to the offspring. Can add to the ageing process or may lead to cancer.
        • Meiosis: mutations can be inherited.
      • 2 Main Classes
        • Point/substitution mutations
          • One base pair replaces another.
        • Insertion/deletion mutations
          • One or more nucleotide pairs are inserted or deleted from a length of DNA.
      • The effects on the polypeptide sequence..
        • Missense mutation: causes one AA to swap for another.
        • Nonsense mutation: causes a stop codon to be produced. Protein too short so can't function now.
        • Silent mutation: happens in a non-coding part of DNA or causes the same AA to be put in place.
        • Frameshift: every AA after that point is changed.
      • Diseases
        • CF: deletion of a triplet of base pairs. Effects whole function of Cl¬ pump
        • Sickle-cell An: point=missense on codon 6. Valine instead of glutamic acid.
        • Bladder cancer: point in RAS gene, produces oncogenes = unreg cell div.
        • Huntingtons: repeating CAG sequence (insertion) alters protein
      • Effects
        • Neutral
          • If mutation is in non-coding part or if its a silent mutation
          • If the changed charac gives no particular ad or disad to organism
            • Eg some people can smell honeysuckle flowers and some can't
        • Harmful/beneficial
          • Skin colour
            • Africa, lots of UV light so handy to have dark skin as pigment melanin protects them from UV effects. Could still make vit D
            • More temperate climes.. less intense so dark skin couldn't make vit D.
              • Mutations producing paler skin is an ad as they could make more vit D
            • So diff environ alters whether the mutation is good or bad
    • a random change to genetic material in a cell, could be the amount of or arrangement  of it.
    • May occur during DNA replication. May be caused by substances called mutagens.
      • Tar
      • UV light
      • X-rays and gamma rays.


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