$PCR$ (Polymerase Chain Reaction) is used for the diagnosis of which of the following diseases?

Separation of $DNA$ fragments is done by a technique known as:

Given below are four statements pertaining to the separation of $DNA$ fragments using gel electrophoresis. Identify the incorrect statements:
$(a)$ $DNA$ is a negatively charged molecule and so it is loaded on the gel towards the Anode terminal.
$(b)$ $DNA$ fragments travel along the surface of the gel,whose concentration does not affect the movement of $DNA$.
$(c)$ The smaller the size of the $DNA$ fragment,the larger is the distance it travels through it.
$(d)$ Pure $DNA$ can be visualized directly by exposing it to $UV$ radiation.
Choose the correct answer from the options given below:

What is the charge on $DNA$ and towards which electrode does it migrate during gel electrophoresis?

Which impurities are released along with $DNA$ when cells are broken down for $DNA$ isolation?

In a stirred-tank bioreactor,the stirrer facilitates $........$