Mutations and Meiosis

• Genetic diversity can arise as a result of mutations or during meiosis.
• What are the two way genetic diversity can occur?

  Mutations or during meiosis
• A gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide, and they occur continuously.
• What is a gene mutation?

  A change in the sequence of base pairs in a DNA molecule
• As the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the polypeptide that the gene codes for, they can therefore interrupt the normal functioning of a protein.
• What can a gene mutation cause?


  The interruption of the normal functioning of a protein
• Most mutations do not alter the polypeptide or only alter it slightly so that its structure or function is not changed, this is because the genetic code is degenerate
• Why do most mutations not alter the function of polypeptides?


  The genetic code is degenerate
• A small number of mutations code for a significantly altered polypeptide with a different shape, this may affect the ability of the protein to perform its function.
• What can a mutation code for?

  A significantly altered polypeptide with a different shape, this may affect the ability of the protein to perform its function.
• What are the three types of mutations?


  Addition, deletion and substitution
• Addition mutations are where one or more bases are added to the DNA sequence.
• What are addition mutations?


  When one or more bases are added to the DNA sequence
• When the number of bases changes by a number other than a multiple of 3, a frame shift occurs, this means that the reading frame of the ribosome is changed and all future codons are read wrong.
• What is a frame shift?

  When the reading frame of a ribosome is changed and all future codons are read wrong
• How can a frame shift occur?

  When the number of bases changes by a number other than a multiple of 3
• What mutations cause a frame shift?

  Addition and deletion
• Addition mutations is the most likely to create a non-functional protein
• What is the mutation most likely to create a non-functional protein?

  Addition mutations
• The ribosome reads the codons in order, and does not overlap the codons when it reads.
• Deletion mutations are where one or more bases are removed from the DNA sequence.
• Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for, as it has a knock-on effect by changing the groups of three bases further on in the DNA sequence, this is sometimes known as a frame shift mutation.
• What is a deletion mutation?

  Where one or more bases are removed from the DNA sequence
• A frame shift mutation can dramatically change the amino acid sequence produced from the gene and therefore the ability of the polypeptide to function
• A three base deletion might remove a single codon or remove some bases from two codons, however only one amino acid will be lost or changed from the chain, this can cause a missense or a nonsense mutation.
• Substitution mutations are where one or more bases are changed in the DNA sequence.
• What is a substitution mutation?

  Where one or more bases are changed in the DNA sequence
• Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the triplet, in which the mutation occurs, and thus not having a knock on effect.
• Substitution mutations do not cause a frame shift to occur as the number of bases doesnt change.
• Substitution mutations can take three forms:

  • Silent mutations
  • Missense mutations
  • Nonsense mutations
• What is a silent mutation?


  A mutation that does not result in a change to the amino acid sequence of a protein.
• Silent mutations do not alter the amino acid sequence of the polypeptide, this is because the genetic code is degenerate
• Why dont silent mutations change the amino acid sequence?


  The genetic code is degenerate
• What are missense mutations?


  Mutations that alter a single amino acid in the polypeptide chain
• Missense mutations alter a single amino acid in the polypeptide chain
• What are nonsense mutations?


  A mutation that creates a premature stop codon, causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function
• Nonsense mutations create a premature stop codon, causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function
• What are two of the cause of mutations?

  Mutagenic agents and chromosome mutations
• Causes of mutations include mutagenic agents (e.g. UV light) and chromosome mutations (e.g. deletions)
• When DNA is replicated, the bases in the DNA sequence are read and copied, there can be errors in this process, these cause mutations.