What is agarose gel? How is it used with DNA?
Agarose is a polysaccharide polymer derived from seaweed. It is available as a white powder, which can be used to cast gels for DNA electrophoresis.
To know more about principles behind electrophoresis, go here http://socratic.org/questions/what-is-gel-electrophoresis?source=search
To prepare an agarose gel, a weighed amount of agarose powder is added to TAE buffer (tris-acetate-EDTA) and heated until the powder dissolves. Then, a very small amount of ethidium bromide is added to the hot solution. This solution is then poured in a tray, with a comb to create wells. As the solution cools, it will thicken and form a gel.
This gel is then immersed in the same TAE buffer that was used to cast the gel, in an electrophoresis tank. DNA samples (and ladder) are loaded in the wells and electrophoresis is carried out.
Different concentrations of agarose can be used (usually 0.5% to 2%). A higher percentage has smaller pores and can be used to resolve smaller fragments of DNA
Ethidium bromide binds DNA irreversibly and is highly toxic. Avoid any sort of contact, and dispose responsibly. It lights up under UV light, and this helps visualize DNA bands after electrophoresis.