Pulsed gel electrophoresis is used for-

Ans. is 'a' i.e., DNA* Large DNA of size larger than 15 to 20 KB can be separated with higher resolution by periodically changing the voltage direction. This is called as pulsed gel Electrophoresis.* The rationale behind this technique is that generally for separating DNA of smaller size, the electrode close to the point of application is connected to negatively charged electrode and the other side is connected to positively charged electrode. When the electric current is switched on, the DNA fragments move from negatively charged electrode to positively charged electrode and the separation is based on length. But when the size of the DNA fragments to be separated is more than 15 to 20 KB, they all move together and create a broader band. Hence to improve the resolution, the voltage direction is changed frequently. This is called as pulsed gel electrophoresis. In this case, the larger fragments take longer time to realign and hence they get separated from relatively smaller fragments. Hence resolution for separating larger fragments is increased.