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.

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 one bacterium (the donor) transfers genetic material to another (the recipient). The duration of gene transfer can be used to map the relative positions of genes on the chromosome.

Gene Mapping

Gene mapping is a technique used to determine the relative positions of genes on a chromosome. In interrupted mating studies, the time it takes for genes to be transferred during conjugation indicates their distance from the origin of transfer (oriT). The shorter the time interval for a gene's transfer, the closer it is to the oriT, allowing researchers to create a linear map of gene locations based on transfer times.

Distance Measurement in Minutes

In the context of interrupted mating studies, the distance between genes is measured in minutes, reflecting the time taken for each gene to be transferred from the donor to the recipient. This time correlates with the physical distance on the chromosome, where one minute of transfer time is often interpreted as a specific unit of distance (e.g., 1 minute = 1 map unit). This quantitative approach allows for the construction of a chromosome map based on empirical data from the mating experiments.