ch 8

Gene Transfer

Types of Gene Transfer

  • Vertical Gene Transfer

    • Definition: Transfer of DNA from parent to offspring directly.

    • Description: In sexual reproduction, the DNA of both the mother and father is passed directly to the daughter or son.

    • Significance: DNA inherited is a blend from both parents, establishing genetic lineage.

  • Horizontal Gene Transfer

    • Definition: Transfer of DNA between non-parental organisms.

    • Example: Taking DNA from Escherichia coli (E. Coli) and transferring it to Staphylococcus aureus.

    • Description: Occurs between different organisms that do not share a direct lineage through sexual reproduction.

Recombination in Cells

  • Process of Recombination

    • Occurs during the formation of gametes (sperm and eggs) in a process called meiosis.

    • Meiosis

    • Description: In meiosis, two copies of every chromosome are separated to create gametes with a single copy.

    • Pre-meiosis total: 46 chromosomes. Final outcome: 23 chromosomes in gametes.

    • Crossing Over

    • Definition: Process where two chromosomes, identical in information but with different sequences, exchange genetic material during meiosis.

    • Example: A chromosome from the mother (pink) and father (blue) may swap segments, increasing genetic diversity in offspring.

    • Result: Siblings may share similarities but will not be genetically identical due to recombination.

Malformations in Chromosomes

  • Potential for significant genetic anomalies arises during DNA recombination processes in gamete formation.

  • If recombination introduces large insertion-deletion events, this can lead to malformation in embryos if not corrected in time.

Types of Horizontal Gene Transfer

  • Transformation:

    • Definition: Uptake of free DNA from the environment by a bacterial cell.

    • Historical Experiment: Griffith's experiment with Streptococcus pneumoniae.

    • Observed two strains: smooth (virulent) and rough (non-virulent).

    • Experimentally killed smooth bacteria and mixed with rough bacteria, leading to the rough strain acquiring virulence, indicating DNA uptake from the dead smooth strain.

    • Significance: Demonstrated transformational capability of bacteria to take up genetic material and express new traits (e.g., capsule formation).

  • Transduction:

    • Definition: Involves a virus transferring genes from one bacterium to another.

    • Generalized Transduction:

    • Description: Occurs when a virus accidentally incorporates a piece of the host DNA and transfers it to the next host.

    • Significance: This can introduce new traits, such as antibiotic resistance, to the recipient bacteria.

    • Specialized Transduction:

    • Definition: Involves a virus integrating its genes with specific adjacent host DNA, leading to targeted genetic transfer.

    • Difference: Transfer involves adjacent genetic material next to where the virus integrated into the genome.

  • Conjugation:

    • Definition: Transfer of DNA through direct contact between two bacterial cells, typically through pilus formation.

    • Description: Bacteria can exchange plasmids that carry genes for traits such as antibiotic resistance.

Plasmids

  • Definition: Extra-chromosomal pieces of DNA commonly found in bacteria that are not essential for survival but provide additional traits.

  • **Fertility Plasmids