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.

Use the cotransduction data to determine the order of these genes.

Verified step by step guidance

1. Start by understanding the concept of cotransduction. Cotransduction occurs when two or more genes are transferred together during transduction, and the frequency of cotransduction is inversely proportional to the distance between the genes. Genes that are closer together are more likely to be cotransduced.
2. Examine the table provided. The table shows the cotransduction frequencies for unselected markers when a specific marker is selected. Higher cotransduction frequencies indicate that the genes are closer together.
3. Analyze the data for each selected marker. For example, when phe⁺ is selected, the cotransduction frequency with met⁺ is 2%, and with ara⁺ is 51%. This suggests that phe⁺ is closer to ara⁺ than to met⁺.
4. Similarly, when met⁺ is selected, the cotransduction frequency with phe⁺ is 4%, and with ara⁺ is 7%. This suggests that met⁺ is closer to phe⁺ than to ara⁺.
5. Combine the information to determine the gene order. Based on the cotransduction frequencies, the gene order is likely ara⁺ - phe⁺ - met⁺, as ara⁺ and phe⁺ have the highest cotransduction frequency, indicating they are closest, while met⁺ is farther away.

Key Concepts

Transduction

Transduction is a process of genetic transfer in bacteria where bacteriophages (viruses that infect bacteria) carry DNA from one bacterium to another. This mechanism can lead to genetic recombination and the introduction of new traits, such as antibiotic resistance or metabolic capabilities. Understanding transduction is crucial for analyzing how genes are transferred and how they can be mapped based on cotransduction frequencies.

Cotransduction Frequency

Cotransduction frequency refers to the likelihood that two genes will be transferred together during the transduction process. This frequency is influenced by the physical proximity of the genes on the bacterial chromosome; genes that are closer together are more likely to be cotransduced. By analyzing these frequencies, researchers can infer the relative positions of genes on a chromosome, which is essential for determining gene order.

Genetic Mapping

Genetic mapping is the process of determining the arrangement of genes on a chromosome. It involves using data from experiments, such as cotransduction frequencies, to establish the order and distance between genes. This information is vital for understanding gene interactions, functions, and the overall genetic architecture of an organism, particularly in studies involving mutations and genetic engineering.