Question

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.
Table showing transductant genotypes and frequencies for three experiments selecting for specific E. coli markers.

Table showing transductant genotypes and frequencies for three experiments selecting for specific E. coli markers.

What compound or compounds are added to the minimal medium to select for transductants in Experiments A, B, and C?

Accepted Answer

Step 1: Understand the concept of transduction and selection. Transduction is a process where bacterial DNA is transferred from one bacterium to another by a phage. In this experiment, the phage P1 is used to transfer genetic material between donor and recipient strains. Selection involves growing bacteria on a minimal medium supplemented with specific compounds to identify transductants that have acquired the desired genotype. Step 2: Analyze the genotype being selected in each experiment. In Experiment A, transductants are selected for leu⁺, meaning the medium must contain leucine to allow only leu⁺ bacteria to grow. In Experiment B, transductants are selected for ala⁺, so the medium must contain alanine. In Experiment C, transductants are selected for phe⁺, requiring phenylalanine in the medium. Step 3: Examine the genotype frequencies for unselected markers in each experiment. For Experiment A, the frequencies of phe⁻ ala⁻, phe⁺ ala⁻, phe⁻ ala⁺, and phe⁺ ala⁺ indicate the likelihood of co-transduction of phe and ala with leu. Similarly, for Experiment B and C, the frequencies of unselected markers provide insights into the genetic linkage between leu, phe, and ala. Step 4: Determine the compounds added to the minimal medium for selection. To select for leu⁺ transductants in Experiment A, leucine is added to the medium. For ala⁺ transductants in Experiment B, alanine is added. For phe⁺ transductants in Experiment C, phenylalanine is added. These compounds ensure that only bacteria with the corresponding genotype can grow. Step 5: Reflect on the results and genetic linkage. The frequency data suggests varying degrees of linkage between the genes leu, phe, and ala. Genes that are closer together on the bacterial chromosome are more likely to be co-transduced, as seen in the higher frequencies of certain genotypes. This information can be used to map the relative positions of these genes.

비슷한 문제에 대한 검증된 영상 답변:

주요 개념

Generalized Transduction

Selection of Transductants

Auxotrophy and Prototrophy