agarose gel electrophoresis

[Andreas Rump]

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.


                                         Slot
      |----------------------------------|  |--|
      |              x                   |  |  |
      |                                  |  |  |  Gel, seen from the
      |              y                   |__|  |  side
      |________________________________________|


Has anyone observed the same phenomenon or can explain it?

Sincerely yours,
Andreas Rump.