Mutations

MUTATIONS

  • Definition: Mutations are changes to a DNA sequence, similar to mistakes in spelling that alter the meaning of a sentence.

TYPES OF MUTATIONS

  1. Point Mutation

  2. Frameshift Mutation

MUTAGENS

  • Definition: Mutagens are agents that cause alterations in DNA, potentially leading to permanent mutations depending on an organism's repair mechanisms.

  • Examples of Mutagens:

    • Radioactive substances

    • X-rays

    • Ultraviolet radiation

    • Certain chemicals or drugs

POINT MUTATION

  • Definition: Point mutation is a type of mutation in DNA or RNA where a single nucleotide base is deleted, added, or altered, which may lead to substitution mutations.

TYPES OF POINT MUTATION

A. Nonsense Mutation
B. Missense Mutation
C. Silent Mutation

A. NONSENSE MUTATION

  • Definition: Nonsense mutation results in the formation of a stop codon due to the substitution of one nitrogenous base.

B. MISSENSE MUTATION

  • Definition: Missense mutation occurs when one nitrogenous base in the DNA is replaced, resulting in an altered codon that does not form a stop codon.

Classification of Missense Mutation

  1. Conservative Mutation:

    • Definition: When the new amino acid formed has the same properties as the original amino acid.

  2. Non-Conservative Mutation:

    • Definition: When the new amino acid formed has different properties from the original amino acid.

C. SILENT MUTATION

  • Definition: Silent mutation occurs when a nitrogenous base is altered but results in the production of the same amino acid.

  • Illustration of Silent Mutation:

    • mRNA Sequence:

    • Original: 5' Met Lys Phe Gly Stop 3'

    • Mutation: Base-pair substitution (e.g., U instead of C) resulting in no effect on the amino acid sequence.

  • Example:

    • Base sequence before mutation: TTC (produces LYSINE)

    • Base sequence after mutation: TTT (still produces LYSINE)

FRAMESHIFT MUTATION

  • Definition: A frameshift mutation occurs when the normal sequence of codons is disrupted by the insertion or deletion of one or more nitrogenous bases, provided that the number of bases added or deleted is not a multiple of three.

  • Illustration:

    • Example: If a single nucleotide is deleted, all subsequent codons will have an altered reading frame.

KINDS OF CHROMOSOMAL MUTATIONS

  1. Deletion: Occurs when a base is deleted from the nitrogen base sequence.

  2. Duplication: When a segment of a chromosome is copied too many times, resulting in extra copies of genetic material.

  3. Inversion: When a segment of a chromosome is reversed end to end.

  4. Insertion: Addition of one or more nucleotide base pairs into a DNA sequence.

  5. Translocation: Exchange of segments between two chromosomes.

WHAT HAPPENS WHEN A PERSON HAS MUTATED GENES?

  1. Sickle Cell Anemia:

    • Caused by a recessive disorder from a single substitution mutation in the gene responsible for hemoglobin production, where valine substitutes for glutamic acid, leading to sickle-shaped blood cells.

  2. Albinism (Type I Oculocutaneous Albinism):

    • Caused by a deletion mutation leading to a reduced or absent formation of melanin in skin, hair, and eyes due to lack of activity of the enzyme tyrosinase.

  3. Cystic Fibrosis:

    • A recessive inherited disorder most commonly caused by a deletion mutation affecting the cystic fibrosis transmembrane conductance regulator (CFTR) gene, leading to the deletion of phenylalanine amino acid.

  4. Down Syndrome (Trisomy 21):

    • Characterized by impairment of physical growth and distinct body and facial features. Caused by a translocation during meiosis transferring most of chromosome 21.