Question

A question from my biological practical: How do we improve the accuracy of estimating DNA base pair sizes based on the distance migrated using gel electrophoresis?? Like how do we improve our ways of measuring the distance migrated by DNA samples so that we get the correct base pair sizes from making graph and trend line? Give explanation?

Answer 1

The DNA base pair sizes can be estimated by a process of gel electrophoresis. In this process, the DNA samples are loaded inside the wells on an agarose gel. A potential difference is then applied across the gel. DNA being negatively charge migrates to the positive terminal.

While the DNA is migrating, it experiences resistance by the gel matrix. Smaller fragments experience less resistance and hence migrate further. Larger fragments, on the other hand, experience more resistance and hence end up migrating less.

Therefore, based on the distance that is migrated by the DNA, we can get an estimate on the size of the DNA. However, when the gel is small or the potential difference is less or the time allotted for the bands to separate is less, the heavier bands do not segregate well. Therefore, using a larger gel or applying a larger potential difference across the gel or we can allow the bands to segregate further.

Based on this, we can plot the logarithm of the distance migrated for the know bands on a graph paper. We can then get a trend line for this and using the trend line, we can estimate the size of the unknown bands based on the distance that they have migrated.