Bacteria reproduce by the process of binary fission. In this process, the chromosome in the mother cell is replicated and a copy is allocated to each of the daughter cells. As a result, the two daughter cells are genetically identical. If the daughter cells are always identical to the mother, how are different strains of the same bacterial species created? The answer lies in certain events that change the bacterial chromosome and then these changes are passed on to future generations by binary fission. In this chapter, you will explore some of the events that result in heritable changes in the genome: genetic transfer and recombination, plasmids and transposons.

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Class Notes

[Recombination] [Genetic Transfer] [Transformation] [Griffith's Experiment]

[Transduction] [Conjugation] [Plasmids] [Transposons]


Genetic Transfer


Griffith's Experiment





  • Transposons (Transposable Genetic Elements) are pieces of DNA that can move from one location on the chromosome another, from plasmid to chromosome or vice versa or from one plasmid to another.
  • The simplest transposon is an insertion sequence.
    • An insertion sequence contains only one gene that codes frotransposase, the enzyme that catalyzes transposition.
    • The transposase gene is flanked by two DNA sequences called inverted repeats because that two regions are upside-down and backward to each other.
  • Transposase binds to these regions and cuts DNA to remove the gene.
  • Yhe transposon can enter a number of locations.
    • When it invades a gene it usually inactivates the gene by interrupting the coding sequence and the protein that the gene codes for.
    • Luckil, transposition occurs rarely and is comparable to spontaneous mutation rates in bacteria.
  • Complex transposons consist of one or more genes between two insertion sequences.
  • The gene, coding for antibiotic resistance, for example, is carried along with the transposon as it inserts elsewhere.
  • It could insert in a plasmid and be passed on to other bacteria by conjugation.