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.

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 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 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 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 in what order, allowing them to map the genetic distance between genes. This technique is crucial for understanding gene linkage and the organization of bacterial genomes.

Gene Mapping and Distance Measurement

Gene mapping involves determining the relative positions of genes on a chromosome based on the frequency of recombination events. The time taken for genes to be transferred during conjugation is proportional to their distance on the chromosome; genes that are closer together are transferred more quickly. By analyzing the duration of gene transfer from Hfr strains, one can infer the arrangement and distances between genes, which is essential for constructing genetic maps.