Bmsc210 M2 p4

• – Physical exchange of DNA between genetic elements
• -Selective medium can be used to detect raregenetic recombinants

– Process that results in genetic exchange between homologous DNA from two different sources (Figure 10.10

• – Genetic transfer process by which DNA is incorporated into a recipient cell and brings about genetic change
• - Discovered by Fredrick Griffith in the late 1920s
• – Worked with Streptococcus pneumoniae (pneumococcus; Figure 10.12)
• ? This process set the stage for the discovery of DNA

• -ability of cells to take up DNA and be transformed
• – In naturally transformable bacteria, competence is regulated
• – In other strains, specific procedures are necessary to make cells competent
• – Electricity can be used to force cells to take up DNA (electroporation)

When Electricity is used to force cells to take up DNA

regulated

• – Transfer of DNA from one cell to another by abacteriophage
• – Two modes:
• • Generalized transduction
• • Specialized transduction

• DNA derived fromvirtually any portion of the host genome ispackaged inside the mature virion
• – Defective virus particle incorporates fragment ofthe cell’s chromosome randomly– Virus can be temperate or virulent
• – Low efficiency

DNA from a specific region of the host chromosome is integrated directly into the virus genome

mechanism of genetic transfer that involves cell-to-cell contact– Plasmid-encoded mechanism

• -Donor contains conjugative plasmid
• - recipient does not contain plasmid

• – Circular DNA molecule; ~100 kbp– Contains genes that regulate DNA replication– Contains several transposable elements that allow the plasmid to integrate into the hostchromosome
• – Contains tra genes that encode transfer functions

episome

F⁺

•  Hfr (high frequency of recombination)
• – High rates of genetic recombination between genes on the donor chromosome and those of the recipient

Recipient cell does not become Hfr because only a portion of the integrated F plasmid is transferred by the donor

Identification of recombinant strains requires selective conditions in which the desired recombinants can grow but where neither of the parental strains can grow

Genetic crosses with Hfr strains can be used to map the order of genes on the chromosome (Figure 10.24)