Gene Expression and Regulation - Mutations

Unit 6: Gene Expression and Regulation

LG 37.1: Mutations Affecting DNA Bases and Chromosomes

  • Mutations can impact one or several bases, or even entire chromosomes.
    • They can be classified into several categories based on their characteristics and effects.
Point Mutations
  • Definition: A point mutation, or nucleotide substitution, refers to a change of one base for another.
  • Effects:
    • Non-coding DNA: If the mutation occurs in noncoding DNA, it may have little to no effect on the organism.
    • Protein-coding genes: Effects vary:
    • Silent Mutation: No change in the amino acid sequence.
    • Missense Mutation: Results in a change in the amino acid sequence.
    • Nonsense Mutation: Leads to the introduction of a stop codon, resulting in a shorter protein.
Insertions and Deletions
  • Small insertions or deletions can add or remove bases.
    • If the insertion/deletion is not a multiple of three, it results in a frameshift mutation, changing all downstream codons.
Transposable Elements
  • These are DNA sequences capable of moving within the genome.
  • They may affect gene expression if they insert into or near a gene.
Chromosomal Mutations

  • Involve extensive regions of one or several chromosomes:

    • Can result in deletion or duplication of chromosome regions containing genes.
    • May also cause large segments to move onto different chromosomes.

  • Examples of Chromosomal Mutations:

    • Trisomy 21 (Down Syndrome): Characterized by three copies of chromosome 21.
    • Klinefelter Syndrome: Results from the presence of extra sex chromosomes (XXY).
    • Turner Syndrome: Associated with a missing X or Y chromosome.

  • Ploidy: Refers to the number of complete sets of chromosomes:

    • Diploidy: Two sets of chromosomes.
    • Triploidy: Three sets.
    • Polyploidy: More than two sets (e.g., three, four, etc.).

LG 37.2: Genotype and Phenotype

  • Genotype: The genetic makeup of an organism.
  • Phenotype: Observable characteristics resulting from the genotype and environmental interaction.
Alleles

  • Different sequences of genes are termed alleles.

  • Genotype classifications:

    • Homozygous: Two copies of the same allele.
    • Heterozygous: Two different alleles.
Mutation Effects
  • Types:
    • Neutral: No significant impact on survival or reproduction.
    • Harmful: Decreased chances of survival or reproduction.
    • Beneficial: Increased chances of survival or reproduction.

LG 37.3: Mutation Origins and Genetic Variation

  • Sources of Mutations:
    • Can be inherited, occur spontaneously, or be induced by mutagens.
    • Genetic variation arises from mutations and recombination.
Causes of Mutations
  • Errors in DNA replication or induced by external agents (mutagens).
  • DNA Polymerase: Has a proofreading ability, resulting in rare mutations due to efficient repair mechanisms.
Horizontal Gene Transfer in Bacteria
  • Methods:
    • Conjugation: Transfer of DNA via a pilus, where a plasmid moves between bacteria.
    • Transformation: Uptake of DNA from a dead cell by a living bacterial cell from the environment.
    • Transduction: Viruses can pickup DNA from one bacterium and transfer it to another during infection.