1.4

• Mutations

  Changes in the DNA that can result in no protein or an altered protein being synthesised
• Mutations

  • Can occur in genes or chromosomes
• Single gene mutations

  Alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides
• Substitution mutation

  One DNA nucleotide is swapped for a different one
• Missense mutation

  One DNA nucleotide is swapped for another, resulting in one amino acid being changed for another. This may result in a non-functional protein or have little effect on the protein depending on which amino acid is affected.
• Nonsense mutation

  One DNA nucleotide being swapped for another, resulting in a premature stop codon being produced which results in a shorter protein.
• Splice-site mutation

  Results in some introns being retained and/or some exons not being included in the mature mRNA transcript. This results in extra amino acids added to protein if introns are retained or less amino acids if exons are not included and so the shape of the protein changes making it non functioning.
• Insertion and deletion mutations

  Nucleotide insertions or deletions result in frame-shift mutations, which cause all of the codons and all of the amino acids after the mutation to be changed. This has a major effect on the structure of the protein produced.
• Insertion mutation

  An extra DNA nucleotide being inserted into the sequence.
• Deletion mutation

  A DNA nucleotide being deleted from the sequence.
• Describe the change to the genetic code and the protein formed in:

  Missense Mutations

  Nonsense Mutations

  Splice Site Mutations

  Frame shift mutations
• Chromosome structure mutations

  • Include duplication, deletion, inversion and translocation
• Duplication

  A section of a chromosome is added from its homologous partner.
• Deletion

  A section of a chromosome is removed. No other chromosome is affected.
• Inversion

  A section of chromosome is reversed.
• Translocation


  A section of a chromosome is added to a chromosome which is not its homologous partner.
• Translocation


  • Chronic myeloid leukaemia is caused by a translocation of chromosomes 22 and 9
• The substantial changes in chromosome mutations often make them lethal.
• Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides.
• Frame-shift mutations cause all of the codons and all of the amino acids after the mutation to be changed. This has a major effect on the structure of the protein produced.
• Give an account of chromosome structure mutations

  Duplication

  Deletion

  Inversion

  Translocation