Agarose gel for DNA electrophoresisThis protocol is useful to check the approximate size of a mixture of DNA fragments. For example, after a HMW gDNA extraction, it is good to check that the DNA we extracted is actually high-molecular weight. Another use is for separating PCR amplicons when checking for a mutation. Primers can be designed in such a way that PCR will yield two fragments of different sizes depending on whether a sequence is present or not. If a deletion is present, then the amplified fragment will be smaller than for the DNA where there is no deletion.