mutation

• Gene mutation


  A change that occurs in our DNA sequence, either due to mistakes when DNA is copied or due to environmental factors such as UV light
• Types of gene mutations

  • Point mutation
  • Missense mutation
  • Nonsense mutation
  • Frameshift mutation
  • Deletion
  • Insertion

  
• Point mutation


  • A genetic mutation where a single nucleotide base is changed, inserted, or deleted from a sequence of DNA or RNA

  
• Silent mutation


  • Mutations in DNA that do not have an observable effect on the organism's phenotype

  
• Nonsense mutation


  • A change in one DNA base pair that prematurely signals the cell to stop building a protein, resulting in a shortened protein that may function improperly or not at all

  
• Missense mutation


  • A change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene
• Frameshift mutation


  • A mutation that occurs when the addition or deletion of DNA bases changes a gene's reading frame, shifting the grouping of the bases and changing the code for amino acids, usually resulting in a nonfunctional protein
• Deletion


  • A mutation that changes the number of DNA bases by removing pieces of DNA, which may alter the function of the resulting protein(s)

  
• Insertion


  • A mutation that changes the number of DNA bases in a gene by adding a piece of DNA, which may cause the protein made by the gene to not function properly

  
• Mutations occur at a frequency of about 1 in every 1 billion base pairs
• Everybody has about 6 mutations in each cell in their body
• Mutations


  • They are a major source of genetic variation in a population, increasing biodiversity
  • Some variations may help organisms to survive better
  • Mutations are not always seen as the affected gene may still function
  • Mutations may be harmful, beneficial, or have no effect on the organism
• Gametes

  Sperm and egg cells
• Only mutations in the gametes are passed onto the offspring, while mutations in body cells only affect the organism in which they occur and are not passed onto the offspring
• Chromosome mutations

  • Inversion
  • Translocation
  • Deletion
  • Duplication
• Inversion


  • If two breaks occur in one chromosome, the region between the breaks rotates 180 degrees before rejoining with the two end fragments
• Translocation


  • A portion of a chromosome is relocated, either to a different position on the same chromosome or to a different chromosome
• Duplication


  • A portion of genetic material or a chromosome is duplicated or replicated, resulting in multiple copies of that region
• Deletion


  • A small-scale mutation where one or more nucleotides are lost or deleted from the chromosome
• Duplication results from an unequal crossing-over between misaligned homologous chromosomes during meiosis
• Ring chromosomes are a rare disorder caused by the loss or deletion of genetic material from both ends of the chromosome, followed by the joining of the broken ends to form a ring
• Isochromosomes are an unbalanced abnormality where the arms of the chromosome are mirror images of each other, equivalent to a simultaneous duplication and deletion of genetic material
• Importance of Mutations


  • Source of all genetic variation, which further provides the raw material for evolution
  • Source of many disorders and diseases
  • Useful for probing fundamental biological processes

  
• Somatic mutation


  Occur in the "body" of organism, results in mosaic pattern of cells, but not passed down, mutation occurs in any cells except germ cells, it is not passed down the blood line, i.e NOT HEREDITARY, occurs through MITOSIS

  
• Germ-line mutation


  Occur in cells producing gametes, mutation is typically passed to half of offspring—HEREDITARY, occurs through MEIOSIS
• Types of Gene Mutations (Based on Molecular Nature)

  • Base Substitution
  • Insertions and Deletions

  
• Transition


  Purine (Pu) for Purine (Pu); Pyrimidine (Py) for Pyrimidine (Py), no difference in outcome
• Transversion


  Purine (Pu) for Pyrimidine (Py); Pyrimidine (Py) for Purine (Pu), results to an irregular/ unsual sequence of a codon
• Insertions and Deletions


  Frameshift mutations – disrupts codon pattern, in-frame insertions and deletions – insert or delete number of bases that is divisible by three

  
• Which of the following changes is a transition base substitution?
• Phenotypic Effects of Mutations

  • Forward mutation
  • Reverse mutation
  • Missense mutation
  • Silent mutation
  • Neutral mutation
  • Nonsense mutation

  
• Phenotypic Effects of Mutations

  • Loss of function mutation
  • Gain of function mutation
  • Conditional mutation
  • Lethal mutation
  • Suppressor mutation
• Intragenic


  A mutation in the same gene as original mutation restores function

  
• Intergenic


  Mutation that occurs in the other gene which restores function (sometimes in tRNA genes)

  
• Mutation Rate


  The rate at which a mutation occurs, may be determined under normal conditions, altered conditions, or presence of harmful chemicals
• Mutations can be determined microscopically or through chemical reactions— unless phenotypic characteristics are seen

  
• Microorganisms in culture may have different phenotypic characteristics seen when grown in culture in comparison to the old characteristics that were noted before
• Spontaneous replication errors


  Caused by mispairing through wobble, Wobble base pairing - Pairing in RNA with 2 base pairs that do not follow the complimentary rule of pairing, Strand slippage, Unequal crossing over
• Spontaneous Chemical Changes

  • Depurination - Loss of purine
  • Deamination - Loss of an amino group
• Chemically Induced Mutations

  • Mutagen - A compound that induces mutations
  • Base analogs - Modified bases that function similar to regular bases in base pairing events
  • Alkylating agents - Donate alkyl group
  • Deamination - Nitrous acid
  • Hydroxylamine - Add hydroxyl group
  • Oxidative reaction - Superoxide radicals, Hydrogen peroxide
  • Intercalating agents - Proflavine, acridine orange, and ethidium bromide