In gel electrophoresis,at which end is the sample loaded?

Consider the following statements:
$I.$ In microinjection method,foreign $DNA$ is directly injected into the nucleus of an animal cell or plant cell by using microneedles or micropipettes.
$II.$ Microinjection method is used in oocytes,eggs,and embryos.
$III.$ Electroporation is the formation of temporary pores in the plasma membrane of a host cell by using lysozyme or calcium chloride.
$IV.$ In chemical-mediated gene transfer method,certain chemicals such as $CO_{2}$ help foreign $DNA$ to enter the host cell.
Which of the statements given above are correct?

Which of the following methods are collectively referred to as downstream processing?

$DNA$ can be introduced into any cell by:

Select the correct sequence for $PCR$ (Polymerase Chain Reaction).

Southern blotting is done for