Chapter 8: Mutations

Overview of Mutations

• Mutations refer to changes in DNA.
• Often seen as mistakes but can have positive, negative, or neutral effects.
  • Positive: Beneficial mutations, e.g., antibiotic resistance in bacteria.
  • Negative: Detrimental mutations causing protein malfunctions.
  • Neutral: Genotype changes without affecting phenotype.

Genotype vs. Phenotype

• Genotype: DNA sequence, determines physical traits.
• Phenotype: Observable characteristics, may not change with mutation if the same amino acid is coded despite a different codon.

Types of Mutations

• Duplication: Repetition of a nucleotide.
• Deletion: Removal of a nucleotide.
• Inversion: Flipping of a DNA sequence segment.
• Insertion/Translocation: Segment of DNA inserted into a different place.
• DNA Breakage: Part of DNA is lost.
• Frame Shift Mutations:
  • Caused by insertion or deletion shifting the reading frame of codons.
  • Can result in entirely different amino acids.

Examples of Mutations

• Point Mutation: Single nucleotide change.
  • May or may not change the resulting amino acid.
• Use of letters to illustrate mutations:
  • Duplication: ABCDE becomes ABBCDE.
  • Deletion: ABCDE becomes ACDE.
  • Inversion: ABCDE becomes ADCBE.
  • Translocation: ABCDE becomes ABRSDE.

Frame Shift Mutation Example

• Analogy with sentence: "The dog ate the cat."
  • Deleting 'e' gives "Thd oga tet hec at," showing how reading frame shifts.

Studying Mutations in Bacteria

• Auxotrophs: Bacteria with mutations affecting nutrient synthesis.
• Prototrophs: Normal, unmutated bacteria.
• Fluctuation Test:
  • Designed by Luria and Delbrück.
  • Showed mutations occur spontaneously, not induced by antibiotic presence.

Ames Test

• Toxicology test for mutagens, determines if substances cause mutations or cancer.
• Uses auxotrophic form of Salmonella requiring histidine:
  • Bacteria plated on medium lacking histidine.
  • Chemical tested for mutations; growth indicates mutagenic potential.
  • Results included in material data sheets for safety precautions.

Key Takeaways

• Mutations can spontaneously occur or be induced by external factors (chemicals, radiation).
• Tests like the Fluctuation Test and Ames Test help understand mutation mechanisms and identify mutagenic substances.