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Old 03-04-2012
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DNA Variation of drug-resistance within recombinant progeny

An Hfr donor cell that is resistant to ceftazidime, ampicillin, vancomycin, gentamicin, and tetracycline is cultured with a bacterial strain that is sensitive to all these drugs. When the resultant recombinants are grown in antibiotic-containing medium, 95% of the isolates grow in the presence of ampicillin, 80% in the presence of gentamicin, 75% with tetracycline, 60% with ceftazidime, and 45% with vancomycin. Which of the following best describes the drug-resistance genes of the Hfr donor cell?

A. The drug-resistance genes are in a bacteriophage genome
B. The drug-resistance genes are in a conjugative plasmid
C. The drug-resistance genes are in an episome
D. The gene in the sequence closest to oriT encodes vancomycin resistance
E. The gene in the sequence farthest from the tra operon encodes ampicillin resistance.

Please explain your answer as I have NO CLUE how to approach this question.
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Drug resistance genes are mostly on plasmids so i will choose B
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Old 03-06-2012
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The answer is E.

Can anybody explain this to me?
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Old 06-30-2012
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The answer is E.

In an Hfr x F- transfer, genes are transferred in a linear order. That is, it begins from OriT ( origin of transfer ) and ends towards tra. It takes about 2 hours for a complete transfer to occur, but mating is normally interrupted before transfer is complete. So tra is not transferred and the recepient remains F- and does not become Hfr. therefore, genes closest to the OriT ( like Ampicillin-resistance gene in the case )are more likely to get transferred and genes near tra are not (Vanco-R gene in this case) .
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Old 09-06-2012
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Quote:
Originally Posted by kaym View Post
The answer is E.

In an Hfr x F- transfer, genes are transferred in a linear order. That is, it begins from OriT ( origin of transfer ) and ends towards tra. It takes about 2 hours for a complete transfer to occur, but mating is normally interrupted before transfer is complete. So tra is not transferred and the recepient remains F- and does not become Hfr. therefore, genes closest to the OriT ( like Ampicillin-resistance gene in the case )are more likely to get transferred and genes near tra are not (Vanco-R gene in this case) .
"" 95% of the isolates grow in the presence of ampicillin """ means that only 5 % is resistant to ampcillin
so the answer should be d ??
as 55% will be resistant to vancomycin - so vancomicin will be closet to ori T
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Old 09-06-2012
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Correct Answer

Quote:
Originally Posted by drantably View Post
"" 95% of the isolates grow in the presence of ampicillin """ means that only 5 % is resistant to ampcillin
so the answer should be d ??
as 55% will be resistant to vancomycin - so vancomicin will be closet to ori T
i think you have quite confused with the question....

95% of isolates grow in presence of ampicillin---implies...they are 95% resistant to that antibiotic medium.so, 95% are easily growing in it(though ampicillin is present it is not capable to kill them)......only 5% are sensitive(means 5% are dying..unable to grow)
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