1) An Hfr E. coli contains the following genetic traits: lac+ , kans , his+ , le
ID: 60262 • Letter: 1
Question
1) An Hfr E. coli contains the following genetic traits: lac+ , kans , his+ , leu+ , strr . It is mated with a recipient E. coli that contains the opposite genetic traits. Note that kanS means the absence of the kanamycin resistance gene in the Hfr strain, which will allow growth only of the recipient cells in the presence of kanamycin. This is necessary for marking the transfer of the Hfr traits to the recipient strain. At periodic intervals, conjugation is disrupted and cells are plated onto several types of defined media. Nothing grows at the beginning of the experiment on media containing lactose, kanamycin, and streptomycin as this is the most selective medium, but all cells grow on complex media containing no antibiotic (the least selective medium). Mating is interrupted at the times listed below and the following are some of your observations of growth characteristics on a few of the selective media plates containing the indicated nutrients/antibiotics:
15 min. Growth: kanamycin, glucose, leucine
No growth: kanamycin, lactose, leucine, histidine
30 min. Growth: kanamycin, lactose, leucine
No growth: kanamycin, streptomycin, lactose, histidine
45 min. Growth: kanamycin, lactose
No growth: kanamycin, streptomycin, lactose, histidine
60 min. Growth: kanamycin, lactose
No growth: kanamycin, streptomycin, lactose
75 min. Same results as above.
Place genes in chronological order relative to time of gene transfer from Hfr to donor. What gene was not transferred during the experiment? What is the likely explanation for it not being transferred?
Explanation / Answer
The chronological order of genes relative to gene transfer is Leu- Lac. If you investigate at 15 min the growth is seen in the presence of leucine, at 30 min the growth can be seen in the lactose media.
The gene not transferred during the mating is His gene, which can due to absence of the tra promoter in the upstream of this gene. This inhibits the transfer of the gene into the donor strain.
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