Mutation

Mutations

  • Definition: Changes in the nucleotide sequence of DNA.

  • Occurrence:

    • Can happen in somatic cells (not passed to offspring).

    • Can happen in gametes (eggs & sperm) and be passed to offspring.

Are Mutations Helpful or Harmful?

  • Consequences:

    • Some skin cancers and leukemia result from somatic mutations.

    • Some mutations can improve an organism's survival (beneficial).

  • Types of Mutations:

    • Chromosomal Mutations.

    • Gene Mutations.

Chromosomal Mutations

  • Definition: Changes in chromosome structure or gain/loss of chromosome parts.

  • Types of Chromosome Mutations:

    1. Deletion: A piece of a chromosome is lost due to breakage.

    2. Inversion: A chromosome segment breaks off, flips around, and reattaches backward.

    3. Duplication: A gene sequence is repeated, resulting in multiple copies.

    4. Translocation: Part of one chromosome is transferred to a non-homologous chromosome.

    5. Nondisjunction: Failure of chromosomes to separate during meiosis, leading to gametes with abnormal chromosome numbers.

Nondisjunction Process

  1. Meiosis I: Starts normally; tetrads line up in the middle of the cell.

  2. Nondisjunction Occurs: One set of homologous chromosomes does not separate.

  3. Meiosis II: Occurs normally.

  4. Outcome: All gametes have an abnormal number of chromosomes (one too many or one too few).

Gene Mutations

  • Definition: Change in the nucleotide sequence of a gene.

  • Characteristics:

    • May involve a single nucleotide.

    • Can be caused by copying errors, chemicals, viruses, etc.

  • Types of Gene Mutations:

    • Point Mutations: Change of one base in the sequence.

    • Substitutions: One base substituted for another.

    • Insertions: Addition of a base.

    • Deletions: Removal of a base.

    • Frameshift Mutations: Entire sequence is shifted due to insertions or deletions.

Point Mutations

  • Definition: Involve the deletion, insertion, or substitution of a single nucleotide.

Frameshift Mutation

  • Impact: Inserting or deleting one or more nucleotides changes the “reading frame” of the gene, altering the entire sequence.

  • Example:

    • Original: "The fat cat ate the wee rat."

    • Frame Shift (deletion of "a"): "The fat cat tet hew eer at."

Effects of Frameshift Mutation

  • Amino Acid Sequence Change:

    • Original sequence: ATG GAA GCA CGT (Met Glu Ala Gly).

    • After frameshift mutation: ATG AAG CAC GT (Met Lys His).

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