What are possible reasons to explain why my loaded DNA sampl

What are possible reasons to explain why my loaded DNA sample had a shorter migration distance than a larger standard band on my gel electrophoresis?

Solution

The migration of DNA on the agarose gel is dependent upon following features:

1. The size of the DNA: The larger the size of the DNA, the slower it migrates on the agarose gel. This is because a large DNA would require more time to pass through the sieves of the agarose in the gel and hence take more time to get resolved. On the other hand, a shorter DNA sequence will take lesser time to migrate through the gel and hence will be resolved faster.

2. Complexity of the DNA: Whereas linear DNA migrates faster, coiled or supercoiled DNA migrates slowly. This is because the linear DNA can easily traverse through the pores of the agarose and hence will not get entangled in the agarose. On the other hand, due to larger stereo-specific size of coiled DNA, it will get entangled in the agrose pores and migrate slowly.

Thus, according to the present information, one of the DNA sample has shorter migration distance than a larger strand band on the electrophoresis. This might have taken place due to high structural complexity of this DNA i.e. the test DNA must be coiled or supercoiled in nature. This would have made the DNA to get interrupted in the agarose beads and hence it moved slowly.