Genetics continuation

Mutations

• Definition: Mutations are changes in the DNA sequence of an organism.
• Causes:
• Spontaneous Mutations: Occur naturally without outside influence. The rate for prokaryotes is approximately 1 in 1 billion base pairs replicated or 1 in 1 million genes replicated.
• Mutagens: Chemical or physical agents that increase mutation rates significantly (up to 1 in 10,000 base pairs).

Deliberate Mutations

• Research Purpose: Scientists sometimes induce mutations in bacteria to study the effects on genes and characteristics.

Genetic Transfer

• Types:
• Vertical Gene Transfer: Genes passed from parent to offspring. In bacteria, daughter cells are genetically identical to their parent.
• Horizontal Gene Transfer (HGT): Prokaryotes can acquire genes from other cells within the same generation. This can happen instantaneously, allowing for rapid adaptation.

Types of Horizontal Gene Transfer

1. Transformation:

• Definition: Uptake of free DNA from the environment by a bacterial cell.
• Griffith’s Experiment: Used two strains of Streptococcus pneumoniae (encapsulated and non-encapsulated).
  • Encapsulated bacteria killed mice; non-encapsulated did not.
  • When heat-killed encapsulated bacteria mixed with live non-encapsulated bacteria were injected, mice died, showing that non-encapsulated absorbed DNA for capsule production leading to virulence.
• Implications: Transformation allows bacteria to acquire new traits by absorbing DNA from surroundings, which can include beneficial genes.

1. Conjugation:

• Definition: Direct transfer of DNA between two bacterial cells through a conjugation bridge.
• Mechanism:
  • Mediated by a pilus, especially in gram-negative bacteria.
  • Cells are designated as F+ (fertile, contains F plasmid) or F- (not fertile).
  • During conjugation, F+ bacteria transfer a copy of the fertility plasmid to F- bacteria, making it F+.
  • If HFR (high frequency of recombination) cells conjugate with F- cells, chromosomal DNA rather than plasmid DNA is transferred, leaving F- as the recipient without the plasmid but possibly with new DNA.

1. Transduction:

• Definition: Transfer of DNA from one bacterium to another via bacteriophages (viruses that infect bacteria).
• Mechanism:
  • Virus injects its DNA into a bacterial cell, which can mistakenly package bacterial DNA into new phages.
  • When these phages infect another bacterium, they can transfer the bacterial DNA, which may confer new characteristics.

Laboratory Techniques and Applications

• Exploiting HGT: All three mechanisms of gene transfer can be utilized in lab settings, particularly transformation for genetic engineering and biotechnology applications.
• Plasmids: Circular DNA used in experiments to introduce genes into bacteria, including engineered plasmids for specific traits.
• Competence: Making bacteria competent to absorb plasmids through techniques like heat shock.
• Transposons: Mobile genetic elements that move within a genome, providing mechanisms for genetic variation.

Implications of Gene Transfer

• Antibiotic Resistance: Bacteria can easily share resistance genes through conjugation, posing a serious challenge in medical treatments.
• Genetic Engineering: Techniques derived from natural processes allow the manipulation of bacterial genomes for biotechnology purposes, like producing insulin.

Taxonomy and Classification

• Definitions:
• Taxonomy: Classification of organisms.
• Systematics: Study of evolutionary relationships among organisms.
• Phylogeny: Evolutionary history and relationships.
• Three Domains of Life:
• Archaea (prokaryotes, often extremophiles), Bacteria (true bacteria), and Eukarya (eukaryotic organisms).
• Evolutionary Relationships: Phylogenetic trees indicate relatedness - Eukaryotes are more closely related to Archaea than to Bacteria, indicating shared evolutionary history.

Endosymbiotic Theory

• Theory: Mitochondria and chloroplasts originated from prokaryotic cells engulfed by ancestral eukaryotes, evolving into organelles over time.

Importance of Genetic Recombination

• Allows for immediate genetic variation without the time required for mutations to arise.
• Enables bacteria to adapt rapidly to environmental changes, including developing resistance to antibiotics.

Conclusion

• Understanding these processes and mechanisms is critical for advancements in genetic research, biotechnology, and addressing public health concerns related to antibiotic resistance.