Stirred-tank bioreactors have advantages over shake flasks because they

In the presence of a chromogenic substrate,recombinant bacteria appear as .......

Select the option that represents the correct sequence of steps in $r-DNA$ technology.
$(1)$ Insertion of $r-DNA$ into the host
$(2)$ Isolation of $DNA$
$(3)$ Ligation of $DNA$ fragment into the vector
$(4)$ Culturing the host cells in a medium at a large scale and extraction of the desired product
$(5)$ Isolation of the desired $DNA$ fragment
$(6)$ Fragmentation of $DNA$ by restriction endonucleases

Which of the following is added to precipitate purified $DNA$?

Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction $(PCR)$:

$A$ mixture of fragmented $DNA$ was electrophoresed in an agarose gel. After staining the gel with ethidium bromide,no $DNA$ bands were observed. What could be the reason?