Recombinant $\text{DNA}$ is directly injected into the nucleus of an animal cell by $-$

In this technique,large quantities of biotechnological products such as antibiotics,vaccines,and enzymes are produced by maintaining and growing only the desired microbes/eukaryotic cells in a sterile environment.

Ethidium bromide stained agarose gel is exposed to $.......,$ to observe $\text{DNA}$ as bright orange coloured bands.

What would happen when one grows a recombinant bacterium in a bioreactor but forgets to add antibiotic to the medium in which the recombinant is growing?

Which method is used to introduce $r-DNA$ directly into the nucleus of an animal cell?

When foreign $\text{DNA}$ is inserted into any vector,it results in inactivation of any marker gene. This is used for selection of $......\ :-$