Lecture Notes: Causes of Genetic Mutations

Introduction

• Genetic Mutations
  • Mistakes in a cell's DNA.
  • Two main types:
    • Point Mutations: One DNA base is switched for another.
    • Frame-shift Mutations: Alteration of the reading frame of RNA.

Point Mutations

• Caused by Base Substitution
  • Types of Base Substitution:
    • Transition:
      • Substitution of adenine for guanine (or vice versa).
      • Swap between two purines or between two pyrimidines (cytosine for thymine).
    • Transversion:
      • Adenine or guanine swapped for cytosine or thymine.
      • Purine replaced with a pyrimidine or vice versa.
  • Mispairing (Mismatching):
    • Non-Watson-Crick base pairing.
    • Examples:
      • A pairs with C, G pairs with T.
      • More common between purine and pyrimidine than two purines or two pyrimidines.

Frame-shift Mutations

• Causes
  • Insertion:
    • Extra DNA base is inserted.
    • Changes codon reading frame.
    • Example: Addition of cytosine altering RNA sequence.
  • Deletion:
    • A base is removed from sequence.
    • Alters RNA reading frame.
    • Example: Deletion of thymine changing codon sequence.

Large-scale Mutations

• Occur at Chromosomal Level
  • Affect many genes, not just a few base pairs.
  • Translocation:
    • Gene swapping between nonhomologous chromosomes.
    • Different from crossing over in meiosis.
  • Chromosomal Inversion:
    • Two genes on the same chromosome switch places.
    • Affects gene expression regulation.

Conclusion

• Small-scale Mutations
  • Affect DNA at nucleotide level.
  • Point mutations: Transitions, transversions, mispairings.
  • Frame-shift mutations: Insertions, deletions.
• Large-scale Mutations
  • Affect DNA at chromosomal level.
  • Translocation and inversion.
• Regulation Impacts
  • Changes in gene position affect expression.