Science - Mutations


  • DNA stands for DeoxyriboNucleic Acid
  • DNA has the shape of a double helix (like a twisted ladder)
  • The DNA molecule is made up of repeating components called NUCLEOTIDES
  • Nucleotides consist of three components:
    • A Sugar
    • A Phosphate
    • One of 4 Nitrogenous Bases:
      • Adenine (A)
      • Thymine (T)
      • Guanine (G)
      • Cytosine (C)
      • NOTE: You only need to know the letters, not the full names
  • Adenine can only pair with Thymine, while Guanine can only pair with Cytosine
  • Nitrogenous bases pair through Hydrogen bonds
  • DNA contains all the instructions to create an organism
  • Key term: POLYPEPTIDE, also known as a protein
  • DNA is read in groups of three, called a CODON or a triplet


  • A MUTATION is the alteration of the nucleotide sequence in the genome of an organism
  • A MUTAGEN is a physical or chemical agent that changes the genetic material of an organism, increasing the frequency of mutations in an organism
  • Most mutations are harmless (NEUTRAL)
  • Mutations that improve survivability are called BENEFICIAL mutations
  • Mutations that decrease survivability are called DETRIMENTAL mutations

Examples of mutations


  • Name: CCR-5 HIV Immunity
  • How does it occur?: Homozygous allele Δ32 (Delta-32) at the CCR-5 gene locus
    • The CCR-5 gene has the Δ32 allele on both chromosomes. Δ32 is a RECESSIVE gene.
  • What is the benefit?: People with this mutation are completely immune to HIV.


  • Name: Sickle Cell Anaemia
  • How does it occur?: recessive allele in the Beta Globin gene
    • The Beta Globin gene has the recessive allele on both chromosomes.
  • What is the detriment?: Sickle Cell Anaemia causes the hemoglobin protein, which carries oxygen in red blood cells, to be malformed. This means that the red blood cell has a significantly lower oxygen capacity, resulting in lack of oxygen to muscles and organs. This also results in the blood cells taking on a sickle shape rather than the normal torus (doughnut) shape. However, Sickle Cell Anaemia provides immunity to malaria, which may explain why it is quite common in Sub-Saharan Africa.
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