Interrupted mating experiment between Hfr and F strains can be used to map the bacterial genes. In the following experiment, an Hfr strain X (azi gal" gly" his lac" leu' thi" thr' str' ton') was mixed with the F strain which is auxotrophic for threonine (thr'), leucine (leu'), glycine (gly), and histidine (his'), is resistant to streptomycin (str), but is sensitive to sodium azide (azi"), and to infection by bacteriophage TI (ton), and is unable to ferment lactose (lac) or galactose (gal). At various time intervals, small aliquots were removed and mixed violently to separate the conjugating cells. The samples were then plated onto selective media to measure the frequency of thr' leu' str recombinants. It was learnt that thr and leu were very close to the origin of replication and str was quite distant from the origin of replication in the Hfr chromosomal DNA. The results obtained are illustrated in the figure below. azi ton lac Ral his gly 5 10 15 20 25 30 35 40 45 Time of conjugation (minutes) (i) What are Hfr strains? (ii) What is the significant difference in DNA transfer in the cross between Hfr and F strains and between F* and F strains? Frequency (%) of Hfr genetic markers among thr" leu transconjugants.

Interrupted mating experiment between Hfr and F strains can be used to map the bacterial genes. In the following experiment, an Hfr strain X (azi gal" gly" his lac" leu' thi" thr' str' ton') was mixed with the F strain which is auxotrophic for threonine (thr'), leucine (leu'), glycine (gly), and histidine (his'), is resistant to streptomycin (str), but is sensitive to sodium azide (azi"), and to infection by bacteriophage TI (ton), and is unable to ferment lactose (lac) or galactose (gal). At various time intervals, small aliquots were removed and mixed violently to separate the conjugating cells. The samples were then plated onto selective media to measure the frequency of thr' leu' str recombinants. It was learnt that thr and leu were very close to the origin of replication and str was quite distant from the origin of replication in the Hfr chromosomal DNA. The results obtained are illustrated in the figure below. azi ton lac Ral his gly 5 10 15 20 25 30 35 40 45 Time of conjugation (minutes) (i) What are Hfr strains? (ii) What is the significant difference in DNA transfer in the cross between Hfr and F strains and between F* and F strains? Frequency (%) of Hfr genetic markers among thr" leu transconjugants.

Biology: The Dynamic Science (MindTap Course List)

4th Edition

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter17: Bacterial And Viral Genetics

Section: Chapter Questions

Problem 1ITD

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Origins of transfer can be located in many different locations, and their direction of transfer can be clockwise or counterclockwise. Let’s suppose a researcher conjugated six different Hfr strains that werethr+ leu+ tons strr azis lac+ gal+ pro+ met+ to an F− strain that wasthr− leu− tonr strs azir lac− gal− pro− met−, and obtained the followingresults:Draw a circular map of the E. coli chromosome that shows thelocations and orientations of the origins of transfer in these sixHfr strains.
In E. coli, four Hfr strains donate the following markers,shown in the order donated:Strain 1: M Z X W CStrain 2: L A N C WStrain 3: A L B R UStrain 4: Z M U R BAll these Hfr strains are derived from the same F+ strain.What is the order of these markers on the circularchromosome of the original F+?
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