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).