The general transducing phage P1 is grown on a wild type bacterial strain (cys+
ID: 13487 • Letter: T
Question
The general transducing phage P1 is grown on a wild type bacterial strain (cys+ pyr+ trp+). The resulting phage are mixed with an auxotrophic bacteria that require cysteine, pyrimidine, and tryptophan (cys- pyr- trp-). The auxotroph cannot synthesize these molecules due to the mutation; therefore the only way that they can survive is for you to supplement their diet with them. Recombinants are selected on medium containing pyrimidine and tryptophan. Results are shown below:
Spread on Plate Colonies arising on plate
Phage only (108) 0
Recipient cells only (108) 4
Mixture of phage and cells (108 of each) 200
The 200 colonies are tested for growth on various media:
Recombinant Minimal Minimal + Minimal + # of the recombinant
Type Medium Tryptophan Pyrimidine type found
A + + + 0
B - - + 20
C - + - 30
D - - - 150
Total Recombinants = 200
What is the map order of the three mutations?
Explanation / Answer
CO TRANSLATION
cys+ AND trp+
20 cys+ trp+ /200 =10%
cys+ AND pyr+
30 cys+ pyr+ /200 =15%
MAP ORDER
trp --------- cys----------pyr
AS - cys IS CO TRANSDUCIBLE WITH trp AND pyr
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