A triple-auxotrophic strain of E. coli having the genotype phe⁻ met⁻ ara⁻ is used as a recipient strain in a transduction experiment. The strain is unable to synthesize its own phenylalanine or methionine, and it carries a mutation that leaves it unable to utilize the sugar arabinose for growth. The recipient is crossed to a prototrophic strain with the genotype phe⁺ met⁺ ara⁺. The table below shows the selected marker and gives cotransduction frequencies for the unselected markers. Selected Selected Colonies Containing the Marker Unselected Marker (%) _ phe⁺ met⁺ ara⁺ met⁺ 4 - 7 phe⁺ - 2 51 met⁺, phe⁺. - - 79 ara⁺ 68 5 - Use the cotransduction data to determine the order of these genes.

Key Concepts

Transduction

Transduction is a process of genetic transfer in bacteria where bacteriophages (viruses that infect bacteria) transfer DNA from one bacterium to another. This mechanism can lead to genetic recombination and is crucial for understanding how traits can be passed between bacterial strains. In the context of the question, transduction is used to introduce genes from a prototrophic strain into a triple-auxotrophic E. coli strain.

Cotransduction Frequency

Cotransduction frequency refers to the likelihood that two genes will be transferred together during the transduction process. This frequency can provide insights into the physical proximity of genes on a chromosome; genes that are closer together are more likely to be cotransduced. Analyzing cotransduction frequencies helps determine the relative order of genes based on how often they are co-inherited.

Genetic Mapping

Genetic mapping is the process of determining the arrangement of genes on a chromosome. By using data such as cotransduction frequencies, researchers can infer the order of genes and their distances from one another. In this experiment, the cotransduction data will be analyzed to establish the sequence of the genes phe, met, and ara, which is essential for understanding their genetic linkage.