agarose gel electrophoresis

Rod Snowdon Rod.Snowdon at
Thu Mar 20 23:04:45 EST 1997

Andreas Rump wrote:
> Dear Netters,
> I have observed the following phenomenon several times: when I cut
> out a piece of agarose gel containing a single DNA band and place this
> piece of gel on it's side, then I see two bands. This means, that the
> same DNA moves through the gel on two different levels (x and y, see
> Figure), one near the bottom of the gel and one near the surface.
> Both bands are discrete, although the slot has been completely filled
> with sample and one would expect that the DNA enters the gel at the
> whole heigth of the gel and would move as one broad band.
> Has anyone observed the same phenomenon or can explain it?

Normal.  Assuming you've stained by immersing the gel in EtBr after
electrophoresis, it's probably just that the staining solution hasn't
diffused completely into the gel.  Have never bothered myself, but if
you run your sample in an EtBr-gel I would expect you'll see your DNA
samples from top to bottom.


Biometrie und Populationsgenetik
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Tel: (+49)  0641 - 993 7543
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Email: Rod.Snowdon at

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