Assume that the gene trpA in an auxotrophic strain of E. coli is located at 27...

Assume that the gene trpA in an auxotrophic strain of E. coli is located at 27 minutes, whereas the gene pyrE is located at 81 minutes.
Present an experimental scheme that would allow you to convert one of the auxotrophic strains to a prototrophic strain.

A. F⁺ (auxotroph) × F⁻ (wild type)

B. Hfr (auxotroph) × F⁻ (auxotroph)

C. Hfr (auxotroph) × F⁻ (wild type)

D. Hfr (wild type) × F⁻ (auxotroph)

E. F⁺ (wild type) × F⁻ (auxotroph)

The correct answer is D, but I don't understand why. Could someone explain this? Thank you!

Expert Solution

Before I explain why option D is correct, you need to be given an understanding of what auxotrophic and prototrophic strains mean. So, an auxotrophic strain can be seen as a mutant strain that has one or more genes missing that makes them dependent on supplement media in order to synthesise that particular organic compound. On the other hand, a prototrophic strain is a wild type strain that does not have any gene missing and can grow without needing a supplement media.

Now, when you have to convert an auxotrophic strain into a prototrophic (wild type) strain, you will need a bacterium carrying Hfr (prototrophic) which would have all the genes and a F- (auxotrophic). The Hfr, as we know, will convert F- into F+. The resultant F+ would be having all the genes that were missing in F-. Thus, the result of this experiment would be an auxotrophic strain getting converted into a prototrophic strain.

Therefore, option (d) is correct.

gladiator answered 1 year ago

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