EtBr in agarose gels vs. EtBr staining later

[kalch]

In article <D4GKBu.8Ar at midway.uchicago.edu>, rmoldwin at midway.uchicago.edu wrote:


> 
> If I recall correctly, when I tried it, the EtBr migrated in the opposite 
> direction as the DNA.  Also, when you add EtBr to the gel, you can see
that the 
> bottom of the gel is always darker than the top.  I think this is because the 
> EtBr migrates upward.  The implication is that low bp bands at the bottom of 
> the gel may not show up under UV light.  Am I right about this

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yes there is always the problem that you will have to re-stain anyway but
for general purposes its easier to have the EtBr in the gel.
   Another trick is to add a little to the bottom buffer chamber on a long
run to ensure the bottom bands do show up