Editing Agarose gel electrophoresis (section)

===Casting of gel===
[[File:Loading DNA samples into an agarose gel for electrophoresis - CPHST - USDA photo.jpg|thumb|180px|Loading DNA samples into the wells of an agarose gel using a multi-channel pipette.]]

The gel is prepared by dissolving the agarose powder in an appropriate buffer, such as [[TAE buffer|TAE]] or [[TBE buffer|TBE]], to be used in electrophoresis.<ref name=":0" />  The agarose is dispersed in the buffer before heating it to near-boiling point, but avoid boiling. The melted agarose is allowed to cool sufficiently before pouring the solution into a cast as the cast may warp or crack if the agarose solution is too hot. A comb is placed in the cast to create wells for loading sample, and the gel should be completely set before use.

The concentration of gel affects the resolution of DNA separation.  The agarose gel is composed of microscopic pores through which the molecules travel, and there is an inverse relationship between the pore size of the agarose gel and the concentration &ndash; pore size decreases as the density of agarose fibers increases. High gel concentration improves separation of smaller DNA molecules, while lowering gel concentration permits large DNA molecules to be separated. The process allows fragments ranging from 50 base pairs to several mega bases to be separated depending on the gel concentration used.<ref>{{Cite book|title=Gel Electrophoresis|last=Magdeldin|first=Sameh|publisher=InTech|year=2012|pages=35–40}}</ref>  The concentration is measured in weight of agarose over volume of buffer used (g/ml). For a standard agarose gel electrophoresis, a 0.8% gel gives good separation or resolution of large 5–10kb DNA fragments, while 2% gel gives good resolution for small 0.2–1kb fragments. 1% gels is often used for a standard electrophoresis.<ref>{{cite web|title=Agarose gel electrophoresis (basic method) |url=http://www.methodbook.net/dna/agarogel.html|work=Biological Protocols|access-date=23 August 2011}}</ref> High percentage gels are often brittle and may not set evenly, while low percentage gels (0.1-0.2%) are fragile and not easy to handle. Low-melting-point (LMP) agarose gels are also more fragile than normal agarose gel.  Low-melting point agarose may be used on its own or simultaneously with standard agarose for the separation and isolation of DNA.<ref>{{cite journal | vauthors = Fotadar U, Shapiro LE, Surks MI | title = Simultaneous use of standard and low-melting agarose for the separation and isolation of DNA by electrophoresis | journal = BioTechniques | volume = 10 | issue = 2 | pages = 171–2 | date = February 1991 | pmid = 2059440 }}</ref> PFGE and FIGE are often done with high percentage agarose gels.