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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.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
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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 gal his gly 5 10 15 20 25 30 35 Time of conjugation (minutes) 40 45 (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? (iii) How do you separate the thr leu" str recombinants from the Hfr cells used in this experiment? (iv) Based on the experimental results above, what is the order of the genes in the Hfr chromosome and what are the distances (in minutes) between these genes? (v) Is it possible to detect thr' his' recombinants after 25 minutes? Explain how you determine the presence of gal cells from thr leu str recombinants. Frequency (%) of Hfr genetic markers among thr" leu transconjugants.
Transcribed Image Text: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 gal his gly 5 10 15 20 25 30 35 Time of conjugation (minutes) 40 45 (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? (iii) How do you separate the thr leu" str recombinants from the Hfr cells used in this experiment? (iv) Based on the experimental results above, what is the order of the genes in the Hfr chromosome and what are the distances (in minutes) between these genes? (v) Is it possible to detect thr' his' recombinants after 25 minutes? Explain how you determine the presence of gal cells from thr leu str recombinants. Frequency (%) of Hfr genetic markers among thr" leu transconjugants.
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