Mutations in DNA

• Random change in DNA sequence or genetic material
• types of mutations
  • gene: changes in a single gene
  • chromosomal: changes in the whole chromosome
• caused by errors in
  • replication
  • transcription
  • cell division
  • External agents (mutagens)
  • chemicals
  • Radiation
  • Viruses
• point mutations
  • occur at a single point in the DNA sequence
  • DNA → TAC GCA TGG AAT
  • RNA → AUG CGU ACC UUA
  • AA → MET ART THR LEU
  • A substitution occurs and C is being substituted with T
  • DNA → TAC GTA TGG AAT
  • RNA → AUG CAU ACC UUA
  • AA → MET HIS THR LEU
• Frameshift mutations
  • occurs when a nucleotide is deleted or inserted in a DNA strand
  • Bases are still read in groups of 3, so.. it shifts the reading of all of the codons from that nucleotide on
  • DNA → TAC GCA TGG AAT
  • RNA → AUG CGU ACC UUA
  • AA → MET ART THR LEU
  • But how does this affect the proteins being made?
  • DNA → TAT CGC ATG GAA T
  • RNA → AUA GCG UAC CUU A
  • AA → ILE ALA TYR LEU
  • Insertion and deletion
• Chromosomal mutations
  • changes in number or structure of chromosomes
  • result: change in location and/or number of genes
  • Types of chromosomal changes:
  • Deletion: loss of all or parts of a chromosome
  • Duplication: extra copies of parts of a chromosome
  • Inversion: reverse the direction of part of a chromosome
  • Translocation: part of one chromosome breaks off and attaches to a different chromosome
• significance of Mutations
  • neutral- Many have little or no effect
  • Harmful- dramatic changes in protein structure or gene activity
  • defective proteins that disrupt normal biological activity
  • Beneficial- mutations are the source of variation
  • some lead to a characteristic that helps an organism survive better in a changing environment
• Impact on offspring
  • mutations can happen in both body cells and gametes (germ cells)
  • Body cell mutations
  • only affect organism
  • Germ cell mutations
  • passed onto offspring
  • source of genetic variation

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