Mutations

• What Are Mutations ? 


  A mutation is a change in the DNA of a cell

  Mutations can alter a protein, or even stop it being produced.

  Mutations are random, spontaneous and rare, occurring at a rate of 0.003 mutations per genome per cell generation in bacteria

  Mutagens are factors that can increase the rate of mutation.

  Mutagens include ionising radiation as well as some chemicals.
• Single Gene Mutations

  Single gene mutations involve changes to the numbers or the sequence of nucleotides within a single gene.

  Single gene mutations are also known as point mutations.

  There are three types of gene mutations :

  Substitution

  Insertion

  Deletion
• Substitution Mutations

  Substitution mutations are when one nucleotide is substituted for another.

  
  

  Substitution mutations may cause an incorrect amino acid may be inserted into a protein.

  
  

  Usually these changes are minor, but they can cause major problems in some cases i.e. sickle cell anemia
• Insertion Mutation

  These are caused by the addition of one or more nucleotides into a section of DNA.

  This can have drastic effects on the protein which is produced because all the subsequent triplets are read incorrectly

  Insertion mutations are an example of a frameshift mutation.
• Deletion Mutations


  These are caused by the removal of one or more nucleotides from a section of DNA.

  This can have drastic effects on the protein which is produced because all the subsequent triplets are read incorrectly.

  Deletion mutations are another example of a frame shift.
• Effects of mutations.


  The effects of a substitution mutation varies depending on where they occur

  Some effects of substitution mutations include :

  Missense

  Nonsense

  Splice site mutations
• Effects of mutations : Missense

  In Missense Mutations one amino acid is changed for another

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

  Although all amino acids are different, they fall into groups according to their chemical behaviour

  Changing the code but getting an amino acid of the same type can cause little charge. This is neutral.

  If the mutation changes the base but still codes for the same amino acid, this is said to be silent.

  Sickle cell disease is caused by a missense mutation.
• Effects of mutations : Nonsense 


  A nonsense mutation results in the code for an amino acid being changed to a stop codon.

  This can result in an abnormally short protein which may not function properly.

  
  

  Duchanne Muscular Dystrophy is caused by a nonsense mutation.
• Effects of mutations : Splice - Site

  Splice-site mutations result in some introns being retained and/or some exons being included in the mature transcript.

  This can result in a non-functional protein.

  Splice Site mutations such as these alter post-transcriptional processing.
• Mutations in Chromosome structure

  Chromosomal structure mutations involve the breakage of one or more chromosomes.

  Breakages create 'sticky' ends of chromosomes that can join to other 'sticky' ends.

  Because there are substantial changes, they are often lethal.

  There are four types of structure mutation :

  Deletion

  Inversion

  Duplication

  Translocation
• Deletion


  A deletion mutation is when a section of a chromosome is removed
• Inversion 


  An inversion mutation is where a section of chromosome is reversed.
• Duplication


  A duplication mutation is when a section of a chromosome is added from its homologous partner.
• Translocation 


  A translocation is when a section of a chromosome is added to another chromosome, NOT its homologous partner.