You have extracted DNA from various food sources (shown in column 3 of the table

Question

You have extracted DNA from various food sources (shown in column 3 of the table at the top of the next page) and set up the following PCR reactions, where the universal plant primers target a gene coding for a protein involved in photosynthesis and yield a 455 bp PCR product, and the GMO primers target two promoters commonly used in plant transgenes (the same ones targeted by the PCR primers in lab) and yield PCR products of similar size (about 215 bp). After PCR and gel electrophoresis, the gel looks like the one shown below. (a) Which of your PCR reactions were positive controls? Did they work? (b) Wich of your PCR reactions were negative controls? Did they work? (c) If any of the controls did NOT work, what do you think might have gone wrong? (List at least 3 possible explanations. (d) The GMO primers used are actually comprised of two different primer sets that target two different common plant transgenes. Knowing what you do about PCR, what must be true of these two primers sets in order for them to be "multiplexed" (used in the same PCR reaction) successfully? Explain. (e) Describe in detail an alternative method to do the same.

Explanation / Answer

Answer:

a. Reactions 1, 2, 3, 5, and 7 were positive controls. All of them worked except for reaction 7. The Zanzibar papaya

DNA extract should have yielded a PCR product with the universal plant primers but did not.

b. Reaction 4 was a negative control. It did “work” because the PCR reaction was not productive.

c. Reaction 7 did not work. Possible explanations:

(1) I did not perform the DNA extraction from the papaya correctly.

(2) I forgot to add one of the reagents to PCR reaction number 7.

(3) When I loaded the gel, I failed to get any of the sample into well 7.

d. The PCR primers must all have approximately the same melting temperature so that the annealing temperature used in the reaction will work for both primer sets.

(Answered only the first 4 sub-parts according to the rules of Chegg)

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.