Two-dimensional gel electrophoresis is a technique that would allow one to determine the relative sizes of dna fragments .Therefore option A is correct.
Gel electrophoresis is a laboratory system used to separate fusions of DNA, RNA, or proteins according to molecular size. In gel electrophoresis, the motes to be separated are pushed by an electrical field through a gel that contains small pores. The motes travel through the pores in the gel at a speed that's equally related to their lengths. This means that a small DNA patch will travel a lesser distance through the gel than will a larger DNA patch.
Therefore the correct option is A.
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