Outline the different approaches to fractionating DNA using gel electrophoresis.

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The Answer is Gel electrophoresis can be used to separate DNA fragments according to size. Because of its multiple phosphates, DNA is negatively charged and can be induced to migrate through porous gels by fixing a negative electrode to one end of the gel assembly and a positive electrode to the other end. Because of frictional forces as the DNA migrates through the pores, larger DNA fragments migrate more slowly than smaller ones, allowing size fractionation.
Gels made of agarose are used for separating large DNA fragments but for small DNA fragments, polyacrylamide gels offer superior resolution and are used in standard dideoxynucleotide DNA sequencing methods. Slab gels have sometimes been used capillary gel electrophoresis is often used to separate DNA fragments in modern dideoxynucleotide DNA sequencing and in various mutation detection systems. It involves forcing the DNA fragments to migrate through ultrathin columns of polyacrylamide (as explained in Box 3.3).

Outline the Different Approaches to Fractionating DNA Using Gel Electrophoresis