Elution means

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?

$PCR$ is a useful tool for the early diagnosis of an infectious disease. Elaborate.

When a foreign $DNA$ is introduced into an organism,how is it maintained in the host and how is it transferred to the progeny of the organism?

How many basic steps are involved in the creation of a $GMO$?

Which of the following is $NOT$ included in the downstream processing of recombinant $DNA$ technology?