Mutations

Mutations Overview

• Genetic mutations are changes in the DNA sequence caused by various mechanisms; can be small-scale or large-scale.

Small-Scale Mutations

• Affect individual base pairs or small groups of base pairs.
• Types:
  • Missense: A single base pair change results in a different amino acid, potentially altering protein function.
  • Nonsense: A base pair change results in a premature stop code, leading to a truncated, likely non-functional polypeptide.
  • Silent: A base pair change does not alter the amino acid coded for, so the protein remains unchanged.
  • Frameshift: Insertion or deletion of nucleotides shifts the reading frame, affecting every amino acid coded for after the mutation.

Large-Scale Mutations

• Involve multiple nucleotides, entire genes, or whole chromosome regions.
  • Amplification: Gene or gene group is copied to multiple chromosome regions, increasing gene copies and effects.
  • Chromosomal Translocation: Genes or gene groups move from one chromosome to another, potentially creating new genes.
  • Trinucleotide Repeat Expansion: The number of trinucleotide repeats increases from one generation to the next, becoming unstable.

Causes of Genetic Mutations

• Spontaneous Mutations: Arise from inaccurate DNA replication.
• Induced Mutations: Caused by environmental agents (mutagens) that alter DNA.
  • Chemical Mutagens: Chemicals modify nucleotides, disrupting replication (e.g., tobacco smoke).
  • Radiation Mutagens: Breaks bonds in DNA, causing rearrangements or deletions (e.g., X-rays, UV radiation).

Results of Mutations

• Mutations can be positive, negative, or have no effect.
• Most DNA is non-coding, so many mutations have no effect.