8.1.1 Genetic Mutations

Types of Mutations

1. Substitution Mutations

• A single base is replaced by another.
• May result in:
• Silent mutation: No change in the amino acid due to the degenerate nature of the genetic code.
• Missense mutation: A different amino acid is produced, potentially altering the protein's structure and function.
• Nonsense mutation: The mutation introduces a stop codon, resulting in a truncated, non-functional protein.

2. Insertion and Deletion Mutations

• Insertion: One or more nucleotide bases are added to the sequence.
• Deletion: One or more nucleotide bases are removed from the sequence.
• Both cause a frameshift mutation, altering the reading frame of the genetic code, which typically leads to a completely different and non-functional protein.

3. Duplication Mutations

• One or more bases are repeated, leading to a frameshift and abnormal protein production.

4. Inversion Mutations

• A segment of DNA is removed, reversed, and reinserted into the same location.
• This alters the order of bases, potentially affecting the amino acids coded.

5. Translocation Mutations

• A segment of DNA from one chromosome is removed and inserted into another chromosome.
• Often results in major changes to the organism's phenotype and can disrupt gene regulation.

Causes of Mutations

1. Spontaneous Mutations

• Errors during DNA replication, which occur naturally.

2. Induced Mutations

• Caused by external factors such as:
• Radiation: UV or ionising radiation can break DNA strands or alter bases.
• Chemicals: Mutagens like benzene or asbestos can cause base changes or DNA damage.
• Viruses: Some viruses insert their genetic material into the host DNA, causing mutations.

Effects of Mutations

• Neutral Mutations: No effect on the organism's survival or reproduction.
• Harmful Mutations: Lead to diseases or decreased survival (e.g., cystic fibrosis, cancer).
• Beneficial Mutations: Provide an advantage in certain environments, driving evolution.