Which of the following techniques is most commonly used to separate $DNA$ molecules by size?

Which system is not present in a bioreactor?

Which of the following statements is correct in the context of observing $DNA$ separated by agarose gel electrophoresis?

Palaeontologists unearthed a human skull during excavation. $A$ small fragment of the scalp tissue was still attached to it. Only a little $DNA$ could be extracted from it. If the genes of the ancient man need to be analysed,the best way of getting a sufficient amount of $DNA$ from this extract is:

Identify the labels $X$,$Y$,and $Z$ in the given diagram representing the process of recombinant $DNA$ technology.

What is the ultimate objective of $r-DNA$ technology?