Charter 6 and 10 Lec. 3 Flashcards
Lateral gene transfer
The transfer of genetic material from one organism to another that is not an offspring.
Genetic Recombination
The physical exchange of DNA between genetic elements.
Selective medium can be used to detect rare genetic recombinants.
Three kinds of lateral gene transfer
Transformation
Transduction
Conjugation
Transformation
Uptake of naked DNA.
Discovered by Frederick Griffith in the late 1920’s.
This process set the stage for the discovery of DNA.
Griffith’s experiment
Rough strain –> mouse lives.
Smooth strain–> mouse dies.
heat killed smooth strain–> mouse lives.
rough strain and heat killed smooth strain–> mouse dies.
Transformation: Competent
Cells capable of taking up DNA and being transformed.
- competence is highly regulated.
- procedures are necessary to make cells competent.
- electricity can be used to make cells uptake DNA.
Transformation: Factors promoting transformations
- uptake mechanism and rate
- quantity of environmental DNA
- longevity of environmental DNA
- usefulness and incomparability of DNA
- Various inhibitors
Transduction
Gene transfer by viruses.
Two modes:
-generalized transduction
-specialized transduction: DNA from a specific region integrated directly into virus genome.
Generalized transduction
DNA derived from virtually any portion of host genome packaged inside mature virion.
- virus can be temperate or virulent
- low efficiency
specialized transduction
DNA from specific region of host chromosome integrated directly in virus genome.
- transducing efficiency can be high
- DNA of temperate virus excises incorrectly and takes adjacent host genes
Conjugation: bacterial conjugation
Mechanism of genetic transfer that involves cell to cell contact.
- plasmid encoded mechanism
- donor cell: conjugative plasmid
- recipient cell: no plasmid
Conjugation: F plasmid
Circular DNA molecule.
Contains genes that regulate DNA replication.
Transposable elements.
Contains TRA genes that encode transfer functions.
Conjugation: sex pilus
Essential for conjugation.
-only produced by donor cell.
Conjugation: DNA synthesis
Necessary for DNA transfer by conjugation.
-rolling circle replication
Hfr strains and chromosome mobilization
F plasmid is an episome, can integrate into host chromosome.
Cells possessing nonintegrated F plasmid F+.
Cells possessing Hfr
Hfr strains and chromosome mobilization: presence of F plasmid
Results in alternations of cell properties.
Hfr strains and chromosome mobilization: insertion sequences
Present in both F plasmid and E. coli chromosome.
Plasmid is now part of chromosome.
Hfr strains and chromosome mobilization: does not become Hfr (4)
- Only a portion of the integrated F plasmid is transferred by the donor.
- Hfr strains that differ in integration position of F plasmid in chromosome transfer genes in different order.
- Genetic crosses with Hfr strains can be used to map order of genes on chromosome.
- Identification of recombinant strains requires conditions recombinants can grow but parents can not.
Hfr strains and chromosome mobilization: F plasmid
Previously integrated F plasmids that have excised and captured some chromosomal genes.
Complementation
Merodiploid: bacterial strain that carries two copies of any particular chromosomal segment.
Complementation: process by which a functional copy of a gene compensates for a defective copy.
Complementation Tests
Determines if 2 mutations in same or different genes.
- different (trans)
- same (cis)
Gene transfer in archaea
Archaea contain single circular chromosome.
Genetic manipulation of archaea lags behind bacteria.
Gene transfer in archaea: Examples
Transformation, transduction, and conjugation.
Works well in archaea.
-especially halophiles.
