PPP_Chapter 6 b - CHAPTER 6 Genetic Analysis and Mapping in...

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CHAPTER 6 Genetic Analysis and Mapping in  Bacteria and Bacteriophages Dr. Sanghamitra Mohanty
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AREAS OF FOCUS: o Mechanism of genetic exchange conjugation transformation transduction o Bacteriophages o Genetic recombination and gene mapping
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The adaptation hypothesis proposes that the interaction of bacteriophage and bacterium is essential to the bacterium’s acquisition of immunity to the phage. Exposure to the phage “induces” resistance in the bacteria. Spontaneous mutation that occurs in the presence or absence of phage is considered the primary source of genetic variation in bacteria.
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Selection is the growth of the organism under conditions in which only the mutant of interest grows well, whereas the wild type does not. A prototroph can synthesize all essential organic compounds, and therefore can be grown on minimal medium. Through mutation, an auxotroph has lost the ability to synthesize one or more essential compounds, and must be provided with them in the medium if it is to grow.
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Bacteria have three growth phases: lag phase log phase (exponential growth) stationary phase
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Means Of Genetic Recombination In Bacteria: Conjugation Transduction Transformation
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A sex pilus connects cells during bacterial conjugation
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Bacteria undergo conjugation , in which genetic information from one bacterium is transferred to another it recombines with the second bacterium’s DNA In bacterial conjugation in E. coli , F + cells serve as DNA donors and F cells are the recipients ( Figure 6.6 ). F + cells contain a fertility factor (F factor) that confers the ability to donate DNA during conjugation. Recipient cells are converted to F + .
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Conjugation
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An Hfr (high-frequency recombination) strain has the F factor integrated. An Hfr strain can donate genetic information to an F cell, but the recipient does not become F + . Interrupted matings demonstrated that specific genes in an Hfr strain are transferred and recombined sooner than others ( Figure 6.7 ).
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The chromosome of an Hfr strain is transferred linearly. The gene order and distance between genes can be predicted ( Figure 6.8 ).
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Gene transfer by Hfr strains led to the understanding that the E. coli chromosome is circular ( Figure 6.9 and Figure 6.10 ).
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Q: In an Hfr x F mating, if the order of transfer of loci is leu azi ton
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PPP_Chapter 6 b - CHAPTER 6 Genetic Analysis and Mapping in...

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