Bio+97+Worksheet+7 - colonies, 56 were trp+. In the second...

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Bio 97 Worksheet #7 Conceptual problems : Conjugation , Transformation , Transduction 1) Why is generalized transduction not the best method for initially mapping 2 formerly unknown mutants relative to one another on the bacterial chromosome? 2) How does transformation with fragments of the bacterial chromosome differ from transformation with plasmids in the fate of the donor DNA? 3) In undisturbed matings, why are there so many fewer recombinants with late genes than with early genes? Why are there so few Hfrs? Application of Concepts: 4) An E. coli mating between Hfr trp + his + str-s and F - trp - his - str-r was allowed to proceed for 30 minutes. The mixture was plated on medium containing either (i) streptomycin + tryptophan, or (ii) streptomycin + histidine. In the first case, replica plating revealed that, of the 104
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Unformatted text preview: colonies, 56 were trp+. In the second case, replica plating showed that 10 of the 70 colonies were his+. Which of the following is the best representation of the location of the trp and his genes relative to the origin of transfer (>) of the Hfr chromosome? (The > symbol points away from the markers that enter behind it. Markers to which it points are among the last to be transferred) (a)----his-- > ----trp----(b)----trp---- >----his----(c)----trp----his---- > ----(d)----his----trp---->----(e)---->----trp----his----5) Phage P1 transduction of four markers (the wild-type alleles of a, b, c, and d) showed that the percentages of cotransduction were: a-b: 29 a-c: 2 a-d: 5 b-c: 0 b-d: 1 c-d: 50 What is the order of the markers?...
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Bio+97+Worksheet+7 - colonies, 56 were trp+. In the second...

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