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You are to non-culturally detect the presence of E. coli in the soil from a cow pasture. You do this by extracting the total DNA from a sample of the soil and PCR amplifying with E. coli-specific primers that bind to a gene only found in E. coli that amplify a region of the DNA 167 bp long. Propose a postive sample that could be tested alongside your experimental sample.

A. Known Shigella DNA

B. Water

C. Number of Injections

D. Muscle DNA

E. Known E. coli DNA

I think the answer is (E) Known E. coli DNA. That would be the positive control in this context. For a positive control, you need something that you would know the response for. E. coli specific primers would amplify the known E. coli DNA. Water is obviously wrong. I could be wrong. Am I missing something?

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    $\begingroup$ To the homework close voter: this user has made an attempt to answer, so has fulfilled the requirements of the homework policy. $\endgroup$ – De Novo Mar 18 at 6:13
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Yes, you're correct. The question is asking for a positive sample that would be amplified by E. coli specific primers. Known E. coli DNA would do the trick.

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  • $\begingroup$ Thank you for the clarification!!!! $\endgroup$ – user50592 Mar 18 at 6:22
  • $\begingroup$ @user50592 you're welcome. If you'd like to mark this as the answer, click the gray checkmark next to it. I would also recommend you take the tour and visit help center to learn about this stack exchange site. $\endgroup$ – De Novo Mar 18 at 6:26

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