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
Using the chromosome map you prepared in answer to Problem 17, determine the distance in minutes between each gene on the map.

Verified step by step guidance

1. Step 1: Understand the concept of interrupted mating. Interrupted mating studies involve stopping conjugation at specific time intervals to determine the order and distance between genes transferred from an Hfr strain to a recipient cell. The time at which a gene is first observed in the recipient corresponds to its distance from the origin of transfer (oriT).
2. Step 2: Analyze the data for each Hfr strain. For Hfr strain 1, the genes are transferred in the order: oriT, met, ala, lac, gal. The durations are 0, 2, 8, 13, and 17 minutes, respectively. For Hfr strain 2, the genes are transferred in the order: oriT, met, leu, thr, azi, with durations of 0, 2, 7, 10, and 17 minutes. For Hfr strain 3, the genes are transferred in the order: oriT, gal, pro, trp, azi, with durations of 0, 3, 8, 14, and 19 minutes.
3. Step 3: Calculate the distance between consecutive genes for each strain. For example, in Hfr strain 1, the distance between oriT and met is 2 minutes, between met and ala is (8 - 2) = 6 minutes, between ala and lac is (13 - 8) = 5 minutes, and between lac and gal is (17 - 13) = 4 minutes. Repeat this process for Hfr strains 2 and 3.
4. Step 4: Compare the gene order and distances across the three Hfr strains. Since the origin of transfer (oriT) differs for each strain, the gene order and distances will vary. Use the overlapping data from all three strains to construct a unified chromosome map, aligning the genes based on their relative positions and distances.
5. Step 5: Finalize the chromosome map by integrating the data. Ensure that the distances between genes are consistent across all strains. For example, if a gene appears in multiple strains, its position relative to other genes should match the calculated distances. This unified map will represent the genetic layout of the bacterial chromosome in minutes.

Key Concepts

Hfr Strains and Conjugation

Hfr (high frequency of recombination) strains are bacterial strains that have integrated a plasmid into their chromosome, allowing them to transfer chromosomal genes to a recipient bacterium during conjugation. This process involves direct contact between two bacteria, where genetic material is transferred through a pilus. Understanding Hfr strains is crucial for mapping gene locations based on the timing of gene transfer.

Gene Mapping and Time of Transfer

Gene mapping involves determining the relative positions of genes on a chromosome based on the frequency and timing of their transfer during conjugation. The time it takes for a gene to be transferred correlates with its distance from the origin of transfer (oriT). By analyzing the duration of gene transfer from Hfr strains, researchers can create a chromosome map that reflects the linear arrangement of genes.

Interrupted Mating Technique

The interrupted mating technique is a method used to study gene transfer in bacteria by stopping the conjugation process at specific time intervals. By collecting samples at regular intervals, researchers can determine which genes have been transferred and infer their order and distance on the chromosome. This technique is essential for understanding genetic linkage and the physical arrangement of genes.