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Modern Genetic Analysis Chapter 9. The Genetics of Bacteria and Phages
Bacterial Gene Transfer in Review
1. Gene transfer in bacteria can be accomplished through conjugation, transformation, and transduction by phages.
2. Conjugation, transformation, and generalized transduction have in common one important property. Each process introduces a DNA fragment into the recipient cell; then a double-crossover event must take place if the fragment is to be incorporated into the recipient genome and subsequently inherited. Unincorporated fragments cannot replicate and are diluted out and lost from the population of daughter cells.
3. Sexduction by F factors and specialized transduction by phages are similar processes in that, in each case, a specific and limited set of bacterial genes is introduced into the recipient cell. After transfer, the F factor replicates in the bacterial cytoplasm as a separate entity, whereas specialized transducing-phage DNA is recombined into the bacterial chromosome by a phage-encoded recombination system. In both cases, a partial diploid (merozygote) results.
4. Gene transfer can be used to map the bacterial chromosome. Hfr crosses are first used to localize a mutation to a region of the chromosome. Then, recombinant frequency, generalized transduction, or transformation provides a more exact localization.

The recombination processes of bacteria are summarized diagrammatically in Figure 9-25.

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