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I frequently ran into an issue where the bands of my ladder become skewed. What causes this?

Here's an example: 0.7% agarose gel, 100V, 60 minutes. Same problem occurs with 1%. I loaded 10 ul of a 20 ul PCR reaction.

enter image description here

As you can see, the problem is not smiling per se. The lanes themselves are fairly vertical and straight. Just the bands themselves appear warped. What could cause this issue?

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    $\begingroup$ The ladder and lane next to it look overloaded. Try to use less. Also, if possible, don't use the lanes on the sides of the gels, leave those empty if you can. Are you reusing the buffer? You might need to replace it more often. $\endgroup$ – user137 Sep 2 '14 at 22:26
  • $\begingroup$ 0.2u Filter the solutions you use to make your gels, and don't overload the gel, this is overloaded. $\endgroup$ – rhill45 Sep 3 '14 at 0:19
  • $\begingroup$ @user137 Why do you recommend not using the side lanes? $\endgroup$ – Chris Sep 3 '14 at 6:42
  • $\begingroup$ @Chris It might just be coincidence, but it seems like I'm more likely to get a problem with the ladder if I put it in the side lines. Maybe it's just the electrodes in my gel box, or maybe it was a problem with my early gels before I knew not to overload the lanes, but I avoid the side lanes when possible and have had fewer issues. $\endgroup$ – user137 Sep 3 '14 at 13:56
  • $\begingroup$ I have never seen this problem when the gel box was ok. Boxes which caused multiple gels to run funny usually had problems with the wiring of the electrodes. $\endgroup$ – Chris Sep 3 '14 at 15:02
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If the ladder is on an edge of the gel, it may be a process of different density as a result of how the gel cooled (or was poured too slowly). I've loaded more DNA loaded in a gel and it doesn't cause this kind of warping for me. It may be the buffer of the ladder is different from that used to make the gel. Your bands don't look particularly sharp, so I would suspect that the running voltage is too high and causing the surface of the gel to heat up and therefore "smearing" the bands. Try running the voltage at 75 V for a proportionately longer time to see if this solves your problem.

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