Bacterial and Viral Genetic Systems

• Advantages of using bacteria and viruses for genetic studies

  1. small genome
  2. many progeny
  3. easy growth in laboratory settings
  4. rapid reproduction
• Bacterial Genetic System

  one circular DNA, genomes have one origin of replication, some have plasmids
• Plasmids


  small, extrachromosomal DNA that have their own independent replication and encode a variety of information
• Horizontal Gene Transfer

  transfer of genetic material between unrelated organisms, typically of the same generation
• Mechanisms of Horizontal Gene Transfer in Bacteria

  Transformation, Transduction, Conjugation
• Conjugation

  cell-to-cell contact, sex pilus mediated. When a F+ and F- cell comes into contact, the F factor is replicated and transferred to the recipient cell. The F factor becomes extrachromosomal, if it is integrated into the genome, it becomes an Hfr cell.
• F+ * F+ = 2 F+ cells
• Hfr * F- = Hfr and F- cell
• F' * F- = 2 F' cells
• F' cells

  cells with the F factor that has been excised and formed into plasmid
• F factor


  circular DNA molecule that contains necessary genes
• R plasmids


  responsible for antibiotic resistance gene
• Transduction

  phage-mediated transfer, bacteriophage is the mechanism for transfer, two life cycles
• Lysogenic Cycle


  incorporate DNA into host DNA, genetic material is replicated and passed on
• Lytic Cycle


  Infects host cell, replicates its own DNA and degrades host DNA, and host cell is bursted
• Generalized Transduction


  phages package and transfer any bacterial DNA, only go through the lytic cycle, can be used to map genes
• Specialized Transduction


  transfer of only specific genes, can enter the lysogenic cycle
• Transformation


  uptake of naked DNA from the environment