high voltage vs. low voltage in gel electrophoresis

George Rutherford gruther at bilbo.bio.purdue.edu
Fri Oct 9 15:24:00 EST 1998

In article <6v8rdg$f4j$1 at nnrp1.dejanews.com>, danwong at hongkong.com wrote:

> I am running some PCR products in  0.5% agarose and 0.75% Synergel.  The DNA
> fragments range from 0.4 kb to 23kb - most of them are larger than 1kb.  The
> gel looks good when it was run at 120 volts. However, a smear was seen at the
> high molecular bands when it was run at 48volts. Does anyone know why and how
> to deal with it? Thank you very much!

There's really no way to answer this question without some idea of the
size of the box. Volts per centimeter would be informative. The general
rule is "long time/low voltage/lower percentage gel to resolve larger
products (consider a genomic Southern), short time/high voltage/higher
percentage gel to resolve smaller ones ". This sounds the opposite of what
you describe.


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