Genetic variation in prokaryotes | Khan Academy

Genetic Variation in Prokaryotes

I. Introduction

  • Bacteria reproduce by binary fission, creating genetically identical clones.

  • Genetic variation is necessary for adaptation and survival.

  • Prokaryotes achieve genetic diversity through:

    1. Transformation

    2. Transduction

    3. Conjugation

II. Transformation

  • Definition: Bacteria take up foreign DNA from the environment.

  • Often involves plasmids (small circular DNA).

  • Example: A non-pathogenic bacterium can acquire a toxin gene, becoming pathogenic.

III. Transduction

  • Definition: Viruses (bacteriophages) accidentally transfer bacterial DNA between cells.

  • Process:

    1. A bacteriophage infects a bacterial cell.

    2. Some host DNA gets incorporated into new viruses.

    3. The virus infects a new bacterium, transferring DNA.

  • Archaea have their own viruses that facilitate genetic transfer.

IV. Conjugation

  • Definition: Direct transfer of DNA between bacterial cells via a pilus.

  • Process:

    1. A donor F+ cell (with an F plasmid) connects to an F- recipient.

    2. The pilus pulls the cells together.

    3. A single strand of the F plasmid is transferred.

    4. The recipient becomes an F+ donor, capable of transferring DNA.

  • Analogy: Similar to how a vampire "turns" others into vampires.

V. Transposable Elements (Jumping Genes)

  • Definition: DNA segments that move within or between genomes.

  • Can carry antibiotic resistance and pathogenicity genes.

  • If a transposable element moves from a chromosome to a plasmid, resistance genes can spread rapidly through a population.

VI. Conclusion

  • Bacteria evolve rapidly due to:

    • Short generation times (minutes to hours).

    • Random mutations.

    • Horizontal gene transfer (HGT) via transformation, transduction, and conjugation.

  • This ability helps bacteria adapt quickly, but also contributes to issues like antibiotic resistance.