The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype. Experiment A Experiment B Experiment C phe⁻ ala⁻ 26% leu⁻ ala⁻ 65% leu⁻ phe⁻ 71% phe⁺ ala⁻ 50% leu⁺ ala⁻. 48% leu⁺ phe⁻ 21% phe⁻ ala⁺ 19% leu⁻ ala⁺   0%   leu⁻ phe⁺ 0% phe⁺ ala⁺   3% leu⁺ ala⁺   4% leu⁺ phe⁺   3% Determine the order of genes on the donor chromosome.

Key Concepts

Generalized Transduction

Generalized transduction is a process by which bacteriophages (viruses that infect bacteria) transfer genetic material from one bacterium to another. During this process, a phage can accidentally package bacterial DNA instead of its own and introduce it into a new host cell. This mechanism is crucial for understanding how genes can be exchanged between bacterial strains, which is essential for determining gene order based on the frequency of co-transduction.

Co-transduction Frequency

Co-transduction frequency refers to the likelihood that two genes will be transferred together during the process of transduction. By analyzing the frequencies of different genotypes in the transductants, researchers can infer the relative positions of genes on the chromosome. Genes that are closer together are more likely to be co-transduced, while those that are farther apart are less likely, allowing for the construction of a genetic map.

Genetic Mapping

Genetic mapping is the process of determining the relative positions of genes on a chromosome. In this context, it involves using the results from transduction experiments to establish the order of genes based on their co-transduction frequencies. By comparing the frequencies of different genotypes, one can deduce which genes are linked and their approximate distances from one another, ultimately leading to a clearer understanding of the genetic architecture of the donor strain.