Southern Blotting Technique. Southern Blot. Animation.

This video describes the Southern Blot Method. This method is used in molecular biology for detection of a specific DNA sequence in DNA samples. Southern blotting combines transfer of electrophoresis-separated DNA fragments to a filter membrane and subsequent fragment detection by probe hybridization. These four cells represent different clinical isolates of the same species of bacteria. Each contains plasma DNA but the plasmids in one isolate may not be the same as the plasmids in another isolate. We can purify the plasma DNA from the isolates and use two procedures: Gel electrophoresis and Southern blotting to compare these plasmids. As a first step we can use gel electrophoresis to examine the plasmids in their native form. Blue loading buffer is added to an aliquot of the plasmid sample and the mixture is loaded into wells of a jello-like slab made of a polysaccharide material called agarose. The agarose. contains microscopic pores through which the DNA can travel. An electric current draws the negatively charged DNA through the gel toward the positive electrode. The positions of the DNA on the agarose gel indicate the sizes of the plasmids. Smaller pieces of DNA migrate faster than larger ones through the agarose pores, because larger pieces meet with more resistance. In this example the plasmids in lanes A through D are similar in size. The plasmid in lane C migrates slower than the others, and is therefore a little larger. Although the plasmids in B and D appear...