Bacterial Evolution and Genetic Variation

Overview

Bacteria evolved from a common ancestor 3.5 billion years ago to the most diverse domain.
Two main mechanisms for genetic change:
- Mutations: Permanent changes in DNA sequence passed from parent to daughter cells.
- Lateral Gene Transfer (Horizontal Gene Transfer): DNA sharing between organisms within the same generation.

Neutral/Silent Mutations:
- Occur frequently without affecting protein function.
- Example: Substituting one hydrophobic amino acid for another without affecting protein folding.
Detrimental Mutations:
- Affect protein function severely.
- Example: Truncated proteins due to early stop codons.
Advantageous Mutations:
- Rare but result in better adaptation and survivability.

Spontaneous Mutations:
- Occur during DNA replication.
- Error rate: ~1 in 10,000, but corrected to about 1 in every 1 billion bases.
Induced Mutations:
- Caused by mutagens (chemicals), UV light, ionizing radiation.

Point Mutations:
- Substitution: Changes a single base, potentially altering a protein.
- Silent Mutation: Change in DNA that does not affect the amino acid sequence.
- Nonsense Mutation: A change resulting in a stop codon, truncating protein.
- Missense Mutation: Replacement of one amino acid with another, possibly altering function.
Frame Shift Mutations:
- Caused by insertion or deletion of bases, altering the reading frame of DNA.
- Can lead to entirely different and nonfunctional proteins.

Mutations are inherited and passed through generations.
Accumulation of mutations over time can lead to diseases like cancer.
Mutations in sperm or egg cells can result in genetic differences in offspring (e.g., de novo mutations linked to autism).