This is a test that was done to see what the difference would be between running samples through a longer gel or simply increasing the concentration of the polyacrylamide in a shorter gel.  The percentage of polyacrylamide (8 and 15%) is an indication of how porous the gel is to things moving through it (in this case DNA).  In the thicker (more concentrated) gel the DNA moves more slowly.  Below are the pictures obtained.  In each test the DNA samples were run as close to the bottom of the gel as possible.
 

Here is the 15% polyacrylamide gel that was 16 cm long.  Notice the distance between the separated bands (such as samples 12 and 120). . . .
 

When the separation of the bands found in the samples (such as 12 and 120) are compared there is very little difference between the two gels.  So it appears that it is just as well to run DNA samples through a more concentrated gel (15%) for a shorter distance as to run the samples over a greater distance through a less concentrated (8%) gel.

One benefit of a shorter more concentrated gel is that it is easier to work with.  Besides simply being smaller and easier to move around, a more concentrated gel is easier to work with because it is less fragile and is less easily broken or torn.
 
 

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