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
Explain why azi is the last gene of strain 2 to transfer in the 20 minutes of conjugation time. How many minutes of conjugation time would be needed to allow the next gene on the map to transfer from Hfr strain 2?

Verified step by step guidance

1. Step 1: Understand the concept of interrupted mating studies. These experiments are used to map the order of genes on bacterial chromosomes by stopping conjugation at specific time intervals and observing which genes have been transferred. The gene closest to the origin of transfer (oriT) is transferred first, followed by subsequent genes in order of their physical proximity on the chromosome.
2. Step 2: Analyze the data for Hfr strain 2. The genes transferred in order are oriT, met, leu, thr, and azi, with their respective transfer times being 0, 2, 7, 10, and 17 minutes. Azi is the last gene transferred within the 20-minute conjugation window because it is the farthest gene from oriT among those listed.
3. Step 3: Consider the mechanics of conjugation. The transfer of genes during conjugation occurs sequentially along the chromosome. The time required for a gene to transfer depends on its distance from oriT. If azi is transferred at 17 minutes, the next gene on the map would require additional time beyond 20 minutes to transfer.
4. Step 4: Estimate the time needed for the next gene to transfer. To determine this, you would need to know the distance (in minutes) between azi and the next gene on the chromosome map. This information is not provided directly in the problem, but the time difference between consecutive genes can be used as a reference.
5. Step 5: Conclude that the next gene on the map would transfer after 20 minutes of conjugation time. If the average time interval between genes is consistent (e.g., 3-5 minutes), you can predict that the next gene would likely transfer around 22-23 minutes. However, experimental data would be required to confirm the exact timing.

Key Concepts

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 chromosomal genes to a recipient bacterium during conjugation. This process involves the formation of a pilus that connects two bacteria, enabling the transfer of genetic material. The order and timing of gene transfer can provide insights into the relative positions of genes on the chromosome.

Gene Transfer Timing

The timing of gene transfer during conjugation is crucial for mapping bacterial chromosomes. Genes that are closer to the origin of transfer (oriT) are transferred earlier, while those further away are transferred later. By analyzing the duration of gene transfer, researchers can infer the relative distances between genes, allowing for the construction of a genetic map.

Azi Gene Position

In the context of Hfr strain 2, the azi gene is the last to be transferred, indicating its position on the chromosome is farthest from the oriT. The duration of conjugation required for the next gene to transfer can be estimated based on the transfer times of previously mapped genes. Understanding the sequence of gene transfer helps in predicting the time needed for subsequent genes to be transferred during conjugation.