In order to determine the overall chromosome map for E coli

In order to determine the overall chromosome map for E. coli, four Hfr strains (#1, 2, 3, & 4) were obtained from F+ ancestors. The start times of transfer during conjugation matings with F-strains carrying auxotrophic and fermentation markers were determined for each Hfr strain, as listed. Using the times for transfer of each maker, draw a unified chromosome map of E. coli, showing the order and relative distances between these markers. Place the origin of transfer (site of F insertion) on the map for each Hfr strain. What is the total length of the E. coli chromosome, in transfer minutes?

Solution

The process of assigning genes to particular locations on a chromosome is known as chromosome mapping and the map is called gene map. There are many methods used by scientists to find out the correct location by mapping genes. By using these methods different chromosome maps can be prepared like cytogenetic maps, linkage maps, DNA sequence maps or physical maps. Hfr strain indicates a high frequency of recombinants. The polarity of the Hfr chromosome is determined by the orientation in which F+ is inserted in it. The relative position of chromosomes on a gene can be found out by linkage maps which are measured in time taken by second gene in following the first one during conjugation. Here it is assumed that genes separated by 10 minutes near the entry end are physically same distance apart as the genes separated by 10 minutes at the F attachment site.