Types of mutations

• Substitution of bases:

  • A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
• Substitution of bases:

  • The number of bases stays the same
  • After the substitution all other codons are the same
  • There is no frameshift
• Deletion and insertion of bases:

  • Adds or takes away bases
  • The number of bases increases or decreases
  • There is a frameshift
• Deletion of bases:

  • When a nucleotide is lost from the normal DNA sequence
• Deletion of bases:

  • Usually, the amino acid sequence of the polypeptide is entirely different and so the polypeptide is unlikely to function correctly
  • Because one deleted nucleotide causes all triplets in a sequence to be read differently as each has been shifted to the left by one base
• Frameshifts occur when there is an insertion or deletion
• Mutations that cause frameshifts can often have a larger effect on the protein produced, eg:

  • A change in the primary structure of the protein could have knock on effects to the secondary and tertiary structure of the protein
  • Because the R groups will be different so the ionic and covalent bonds will be different
  • If the protein is an enzyme the active site could change shape which would mean it could no longer form E-S complexes
• Chromosome mutations:

  • Changes in the structure or number of whole chromosomes
• Chromosome mutations can arise spontaneously and take two forms:

  • Changes in whole sets of chromosomes
  • Changes in the number of individual chromosomes
• Chromosome mutations: Changes in whole sets of chromosomes

  • Occur when organisms have three or more sets of chromosomes rather than the usual two
  • This condition is called polyploidy - occurs in plants
• Chromosome mutations: Changes in the number of individual chromosomes

  • Sometimes individual homologous pairs of chromosomes fail to separate during meiosis
  • This is known as non-disjunction and usually results in a gamete having either one more or one fewer chromsome
• Non-disjunction - The failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes