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Modern Genetic Analysis Chapter 9. The Genetics of Bacteria and Phages
Solved Problem

1. | We saw in Chapter 5 how recombination takes place by breakage and reunion of chromosomes. Suppose a cell were unable to carry out breakage and reunion by generalized recombination (it has the mutant genotype rec). How would this cell behave as a recipient in generalized and specialized transduction? First compare each type of transduction and then determine the effect of the rec mutation on the inheritance of genes by each process. See answer

Solution

Generalized transduction includes the incorporation of chromosomal fragments into phage heads, which then infect recipient strains. Fragments of the chromosome are randomly incorporated into phage heads, so any marker on the bacterial host chromosome can be transduced to another strain by generalized transduction. In contrast, specialized transduction includes the integration of the phage at a specific point on the chromosome and the rare incorporation of chromosomal markers near the integration site into the phage genome. Therefore, only those markers that are near the specific integration site of the phage on the host chromosome can be transduced.

Inheritance of markers occurs by different routes in generalized and specialized transduction. A generalized transducing phage injects a fragment of the donor chromosome into the recipient. This fragment must be incorporated into the recipient's chromosome by recombination, using the recipient recombination system. Therefore, a rec recipient will not be able to incorporate fragments of DNA and cannot inherit markers by generalized transduction. On the other hand, the major route for the inheritance of markers by specialized transduction includes integration of the specialized transducing particle into the host chromosome at the specific phage integration site. This integration, which sometimes requires an additional wild-type (helper) phage, is mediated by a phage-specific enzyme system that is independent of the normal recombination enzymes. Therefore, a rec recipient can still inherit genetic markers by specialized transduction.

See question

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