Mutations

• Mutations


  An alteration to DNA sequence chromosome, leading to new characteristics in an organism or their offspring
• Types of mutations


  • Gene
  • Chromosomal
  • Somatic
  • Germline
• Gene mutations


  • Only affect one gene/small section of DNA
  • Doesn’t involve the whole chromosome
  • A change in one (or a few) nucleotide bases
  • Occurs during DNA replication
• Point Mutation


  • A change in 1 base sequence
  • Occurs when nucleotides are added or removed from a section of code, resulting in new codons for different amino acids
• Insertion


  Addition of a nucleotide into a DNA sequence
• Deletion


  A removal of a nucleotide from a DNA sequence
• Somatic mutations


  • Affects specific body cells
  • Not passed onto offspring
  • Involved in cancerous growths
• Germline mutations


  • Occur in gamete cells
  • Individual normally not affected
  • Passed onto offspring
  • Affected embryos are naturally aborted
• Chromosomal mutations


  • Affect more than one gene/part of a chromosome/a whole chromosome
  • Occurs during cell division
  • Causes miscarriage, disease or problems in growth or development
• Types of chromosomal mutations

  • Non-disjunction
  • Translocation
  • Inversion
  • Deletion
  • Duplication
• Non-disjunction


  Chromosome pairs that fail to separate
• Translocation


  A part of a chromosome breaks off and rejoins a different chromosome
• Inversion


  A chromosome breakage and re-arrangement on the same chromosome
• Deletion (chromosomal)


  A sequence of DNA is removed
• Duplication


  A section of a chromosome occurs more than once
• Mutagens


  Increase the rate of changes in DNA
• Causes of mutations


  • Ionising radiation
  • Mustard gas
  • Some antibiotics
  • Formaldehyde
• Damage Mutagens Cause


  • Trigger DNA replication errors
  • Cause DNA breakages/lengthening
  • Block DNA replication/damage DNA structure
  • Chemically react & modify DNA
  • Cells with damaged DNA multiply
• Results in all types of mutations
• Can Include


  • Non-Disjunction
  • Translocation
  • Inversion
• Results in chromosomal mutations

  • Affects whole parts of chromosome
• Results in germline mutation


  • Process where new strands of DNA are made where the DNA unzips and complementary strands are formed
• Results in gene or chromosome mutations

  • Results in somatic or germline mutations
• Mutations Found in Several Family Members

  • Occur in germline cells (gametes)
  • Can only be inherited/passed on to offspring
• Selectively Advantageous Mutation


  • A change in DNA
  • Provides an advantage to a particular genotype
  • Occurs under selective pressure
• Impact of Selection Pressures on Alleles

  • The small population will be subjected to selection pressures
  • Through natural selection, some alleles may disappear
  • The gene pool will change dependent on the type of selection pressure
  • Different environmental pressures result in different alleles being selected for
  • Populations become less like each other depending on which alleles are selected for
• How Mutations Lead to Changes in Allele Frequencies of Gene Pools

  • Mutations introduce new alleles into the population
  • May produce traits favourable to survival
  • Increasing its number in the gene pool