• Mutations are changes in the DNA that can result in no protein or an altered protein being synthesised.

Single Gene Mutations

• Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides.

• Nucleotide substitutions — missense, nonsense and splice-site mutations.

  • Missense mutations result in one amino acid being changed for another. 

    • This may result in a non-functional protein or have little effect on the protein.

  • Nonsense mutations result in a premature stop codon being produced which results in a shorter protein.

  • Splice-site mutations result in some introns being retained and/or some exons not being included in the mature transcript.

• Nucleotide insertions or deletions result in frame-shift mutations.

  • 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.

Chromosome Structure Mutations

• Chromosome structure mutations — duplication, deletion, inversion and translocation.

  • Duplication is where a section of a chromosome is added from its homologous partner.

  • Deletion is where a section of a chromosome is removed.

  • Inversion is where a section of chromosome is reversed.

  • Translocation is where a section of a chromosome is added to a chromosome, not its homologous partner.

  • The substantial changes in chromosome mutations often make them lethal.

• Importance of mutations and gene duplication in evolution.

  • Duplication allows potential beneficial mutations to occur in a duplicated gene whilst the original gene can still be expressed to produce its protein.