Question

Your friend works at the Centers for Disease Control and Prevention and has discovered a brand-new virus that has recently been introduced into the human population. She has just developed a new assay that allows her to detect the virus by using PCR products made from the blood of infected patients. The assay uses primers in the PCR assay that hybridize to sequences in the viral genome.

Your friend is distraught because of the result she obtained (see Figure Q10-45) when she looked at PCR products made using the blood of three patients suffering from the viral disease, using her own blood, and using a leaf from her petunia plant.
You advise your friend not to panic, as you believe she is missing an important control. Which one of the choices listed below is the best control for clarifying the results of her assay? Explain your answer.
(a) a PCR assay using blood from a patient who is newly infected but does not yet show symptoms
(b) a PCR assay using blood from a dog
(c) a PCR assay using blood from an uninfected person
(d) repeating the experiments she has already done with a new tube of polymerase

Answer 1

The best control for your friend’s PCR assay is to use blood from an uninfected person to provide a baseline, ensuring the specificity of the test for detecting the viral genome. Option c is correct.

Step-by-step explanation:

The best control for clarifying the results of your friend’s PCR assay would be to use blood from an uninfected person (option c). This uninfected control is vital because it provides a baseline to compare with the test samples from the patients and other sources (like the petunia plant).

If the PCR assay detects the viral genome in the uninfected control, it suggests that there might be contamination or non-specific binding of primers. If no detection occurs in the uninfected control, it supports the specificity of the assay for the viral genome.

Since PCR is a highly sensitive and specific diagnostic tool that can detect the presence of viral DNA by amplifying specific sequences, having appropriate controls is crucial for accurate interpretation of the results.