Gene Mutation

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Gene Mutation
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Mutation

• Mutation change in DNA sequence
• Causes of mutation

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Spontaneous Mutation
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Spontaneous mutation in gene for a blood
clotting factor, leading to hemophilia.
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Point Mutations

• Point mutation change in one or a few DNA
  nucleotides

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Substitutions
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Examples of Substitutions
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Effects of Substitutions on the Protein Sequence
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Applying Your Knowledge
HbA

• The mutation that leads to Sickle-cell
  Disease (HbS) is a
• Silent Mutation
• Synonymous mutation
• Missense Mutation
• Nonsense Mutation
• None of these

HbS
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Applying Your Knowledge

• The mutation that leads to the insertion of
  valine into HbS is due to a
• Transition
• Transversion
• Both a transition and a transversion
• Neither a transition nor a transversion

HbS
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Frameshift Mutations

• Frameshift mutation deletion or insertion of
  nucleotide bases, not in multiples of three
• Causes a change in the reading frame of codons
  for the protein sequence

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Insertions in multiples of three nucleotides
restore the reading frame.
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Tandem Duplications

• Tandem duplications adjacent or nearby repeat of
  part of a genes sequence

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Expanding Triplet Repeats

• Expanding Triplet Repeats increase in number of
  a specific trinucleotide within a gene from
  generation to generation

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Expansion of the Trinucleotide Repeat for
Huntingtons Disease
Linda (6,22)
Allen (46,13) age 50
Andrew (69,6) age 37
Jama (7,18)
Kristen (64,22) age 40
Ann (64,22) age 39
Greg (11,19)
Bill (8,12)
Debbie (13,6)
Nathaniel (72,19) age 35
Christina (93,7) age 26
Joseph (7,6)
Paula (13,12)
Evan (not tested)
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Applying Your Knowledge

• Substitution
• Frameshift Mutation
• Tandem Duplication
• Expanding Triplet Repeat

• An insertion of one or two nucleotide bases
  causes a _____ .
• Replacing one nucleotide with another causes a
  ____.
• A repeat of part of a genes sequence in a nearby
  region is a ______.

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Repair of DNA
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Repairing UV-Damaged DNA
Use of enzymes to remove and replace region with
thymine-thymine dimer
Use of light and enzymes to reverse
thymine-thymine dimers
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Photoreactivation
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Mismatch Repair Correcting Errors in DNA
Replication
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Xeroderma Pigmentosum Accumulation of DNA Damage
Leads to Skin Cancer
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Applying Your Knowledge

• Mismatch Repair
• Excision Repair
• Photoreactivation

• Method of replacing a DNA region that was damaged
  by radiation or chemicals
• Method that uses white light to repair
  thymine-thymine dimers produced by ultraviolet
  radiation
• Method of replacing DNA region where a nucleotide
  was incorrectly placed during replication