A number of DNA diagnostic tests rely on the Southern blot, a method in which DNA samples are made single-stranded by brief exposure to high pH. Which of the following best accounts for separation of the DNA strands under these conditions?

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High pH disrupts the hydrogen bonds between the complementary bases in DNA, leading to the separation of the DNA strands.  Southern blotting is the analysis of DNA structure following its attachment to a solid support. The DNA to be analyzed is first digested with a given restriction enzyme, then the resultant DNA fragments are separated in an agarose gel. The gel is treated with NaOH to denature the DNA, then the NaOH is neutralized. The DNA is transferred from the gel to nitrocellulose or nylon filter paper by either capillary diffusion or under electric current. The DNA is fixed to the filter by baking or ultraviolet light treatment.

A Number of DNA Diagnostic Tests Rely on the Southern