USMLE-Rx Step 1 Qmax Challenge #1226

Check out today’s Step 1 Qmax Question Challenge.

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A 23-year-old female patient who is a carrier of sickle cell trait presents to the clinic. In this patient’s case, the single base-pair mutation for sickle cell anemia destroys the MstII restriction enzyme recognition site represented by an asterisk (*) in the image below. The restriction enzyme-binding sites are shown as arrows on the map. DNA is taken from this carrier patient and is treated with MstII and run on an electrophoresis gel. The DNA is then hybridized with a labeled probe that binds to the gene in the position shown on the map.

In the Southern blot shown to the right in the image above, which lane represents the patient?

A. A
B. B
C. C
D. D
E. E
F. F

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