An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.
Hfr strain 1     oriT  met  ala  lac  gal
Duration (min)   0     2    8   13   17
Hfr strain 2     oriT  met  leu  thr   azi
Duration (min)   0     2    7   10   17
Hfr strain 3     oriT  gal   pro  trp   azi
Duration (min)   0     3    8   14   19
Write out the interrupted mating results you would expect after 20 minutes of conjugation for Hfr strains 4 and 5. Use the format shown at the beginning of this problem.

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Identify the key concept: Interrupted mating studies are used to map the relative positions of genes on a bacterial chromosome by determining the order and timing of gene transfer during conjugation. The time at which a gene is transferred corresponds to its distance from the origin of transfer (oriT).

Analyze the data for Hfr strains 1, 2, and 3. Note the order of genes and the time intervals for each gene transfer. For example, in Hfr strain 1, the order is oriT, met, ala, lac, gal, and the times are 0, 2, 8, 13, and 17 minutes, respectively.

Understand that Hfr strains 4 and 5 will have different starting points (oriT) on the circular bacterial chromosome. The order of genes transferred will depend on the location of oriT and the direction of transfer. Use the data from strains 1, 2, and 3 to infer the possible gene order for strains 4 and 5.

Predict the gene order and transfer times for Hfr strains 4 and 5. For example, if oriT in strain 4 is located near a different gene (e.g., gal), the order might start with gal and proceed to adjacent genes in the direction of transfer. Similarly, for strain 5, oriT might be near another gene (e.g., thr), and the order would reflect that starting point.

Write out the expected interrupted mating results for strains 4 and 5 in the same format as provided in the problem. Include the gene order starting from oriT and the approximate times for each gene transfer based on the distances inferred from the other strains.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hfr Strains and Conjugation

Hfr (high frequency of recombination) strains are bacterial strains that have integrated a plasmid into their chromosomal DNA, allowing them to transfer genetic material to other bacteria through conjugation. During this process, a donor bacterium forms a pilus to connect with a recipient bacterium, facilitating the transfer of chromosomal genes. The order and timing of gene transfer can provide insights into the relative positions of genes on the chromosome.

Interrupted Mating Technique

The interrupted mating technique is a method used to study gene transfer during bacterial conjugation. By interrupting the mating process at specific time intervals, researchers can determine which genes have been transferred based on the duration of conjugation. This allows for the mapping of genes on the bacterial chromosome, as genes that are transferred earlier are located closer to the origin of transfer (oriT).

Gene Mapping and Distance Measurement

Gene mapping involves determining the relative positions of genes on a chromosome based on their transfer frequencies during conjugation. The distance between genes is often measured in minutes of conjugation time, with closer genes being transferred in shorter time intervals. This quantitative approach helps in constructing genetic maps, which are essential for understanding gene function and interactions within the genome.

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