113lecture1506

113lecture1506 - BIOLOGY 113 - MICROBIOLOGY Lecture 15:...

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BIOLOGY 113 - MICROBIOLOGY Lecture 15: Microbial Genetics - Genetic transfer and recombination in bacteria Genetic recombination refers to processes by which new genetic information is provided to a cell - Genetic recombination may involve exchange of genes between molecules, which generates new combinations of genes on a chromosome = Homologous sequences in two DNA molecules may undergo a process of breaking and rejoining - crossing over - and thus exchange sequences (Tortora et al., Figure 8.23) = Crossing over occurs during meiosis in eukaryotes and during the processes of transformation, Hfr-mediated conjugation and transduction (see below) in prokaryotes - Genetic recombination may also involve acquisition of DNA for which there is no homologous DNA in the "recipient", as in most bacterial plasmid transfers - In a sense, a zygote is a recombinant cell since it contains a combination of genes not found cells of either parent Genetic material can be transferred between bacteria in several ways; all of these ways are fundamentally different from the process of mating by which genetic recombinants are generated in eucaryotic organisms - In eukaryotes, we consider two "parents" making an equal contribution to the recombinant genome of their "progeny" - In bacteria, transfer of genetic material is one-way, from donor to recipient = The donor provides (not necessarily of its own volition!) a fragment of its DNA = The recipient has its genotype changed through recombination of its genome with the DNA from the recipient In 1928, Frederick Griffith demonstrated that live cells of an avirulent strain of Streptococcus pneumoniae could be transformed by something (later shown to be DNA) from dead cells of a virulent strain of the same species (Tortora et al., Figure 8.24) - These experiments employed two strains of S. pneumoniae
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113lecture1506 - BIOLOGY 113 - MICROBIOLOGY Lecture 15:...

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