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• Mutation


  A permanent change in the genetic material of an organism
• All mutations are heritable. They will be copied during DNA replication
• Not all mutations are passed on to the next generation
• Only germ cell mutations (in sex cells) will be passed on to future generations
• Somatic cell mutations (in body cells) will not be passed on to offspring, but are passed on to new cells created in the organism
• Types of Mutations


  • Gene Mutations
  • Chromosome Mutations
• Gene Mutations


  Mutations that occur when one or a few nucleotides are changed within a gene, often referred to as Point Mutations
• Types of Point Mutations

  • Substitution
  • Frameshift
• Substitution


  The replacement of one nucleotide for another
• Substitution Mutation


  • Original: The fat cat ate the wee rat.
  • Substitution: The fat hat ate the wee rat.
• Effects of Substitution Mutations

  • Silent Mutation
  • Mis-sense Mutation
  • Nonsense Mutation
• Frameshift


  The insertion or deletion of one or two nucleotides within a sequence of codons, causing the entire reading frame of the gene to be altered
• Frameshift Mutation


  • Original: The fat cat ate the wee rat.
  • Frameshift (deletion): The fat caa tet hew eer at.
• Chromosome Mutations


  Mutations affecting entire chromosomes, parts of chromosomes or multiple genes on the same or different chromosomes, leading to the rearrangement of genetic material
• Types of Chromosome Mutations

  • Transposons (Jumping Genes)
  • Deletion
  • Inversion
  • Duplication
  • Translocation
  • Nondisjunction
• Transposons (Jumping Genes)


  Genes that are able to move (jump) from one area in the DNA to another, leading to tremendous variety in organisms
• Transposons


  • Indian Corn has a variety of colours because of transposons
• Deletion


  A portion of a chromosome is lost, often caused by viruses, radiation, or chemicals
• Deletion


  • Chromosome #5 - When a piece is lost, children are born mentally handicapped and with a cat-like voice (cri-du-chat syndrome)
• Inversion


  A segment of a chromosome may break free and "reverse" its orientation and then become reconnected to the chromosome
• Duplication


  A gene sequence may duplicate itself one or more times within one or several chromosomes, which can affect the functioning of a gene
• Duplication


  • Fragile X Syndrome - The X chromosome has several repeating units of nucleotides (700)
• Translocation


  A part of one chromosome changes places with another part of the same chromosome or with a part of another chromosome (non-homologous)
• Translocation


  • Cancer may occur when part of Chromosome #14 exchanges places with Chromosome #8
  • Some Down's syndrome is related to translocation between Chromosome #14 & 21
• Nondisjunction


  The failure of homologous chromosomes to separate during meiosis, resulting in a cell with either too many or too few chromosomes
• Types of Nondisjunction


  • Trisomy
  • Monosomy
• Trisomy


  When an extra chromosome is inherited in a cell, resulting in 3 chromosomes of the same number in a cell
• Trisomy


  • Trisomy 21 (Three #21 chromosomes) causes Down's Syndrome
• Monosomy


  When only one chromosome is inherited instead of a pair in a cell
• Causes of Mutations


  • Spontaneous Mutations
  • Induced Mutations
• Spontaneous Mutations


  Mutations caused by molecular interactions that occur naturally within cells (e.g. DNA polymerase errors)
• Induced Mutations


  Mutations caused by agents outside the cell (e.g. mutagens - anything that increases the instances of mutations)
• Types of Induced Mutations

  • Physical Mutagens
  • Chemical Mutagens
• Physical Mutagens


  Mutagens that cause physical damage to DNA (e.g. radiation in the form of UV, X-rays, and gamma rays)
• Chemical Mutagens


  Mutagens that react with DNA within the nucleus (e.g. carcinogens)
• Epigenetics


  The study of how behaviors and environment can cause changes that affect the way genes work, without changing the DNA sequence
• Epigenetic changes affect gene expression to turn genes "on" and "off"
• Epigenetic changes such as methylating DNA and modifying histones can turn off a gene, while demethylating DNA and unwrapping histones can turn genes on
• Human Genetic Diseases


  • Down's Syndrome (Trisomy 21)
  • Turner Syndrome (XO)
  • Klinefelter Syndrome (XXY)
  • Jacobs Syndrome (XYY)
  • Triple X Syndrome (XXX)
• Karyotype


  A picture showing the size and arrangement of chromosomes inside the cell of an organism, used to diagnose genetic disorders