In gel electrophoresis,the $DNA$ fragments separate according to ........

What treatment is given to make a bacterial cell competent to take up $DNA$?

In $PCR$ technique,how many copies of the $DNA$ sample will be obtained after $6$ cycles are completed?

$A$ : Taq Polymerase is involved in $PCR$ technique.
$R$ : This enzyme remains active during the high temperature including denaturation of double stranded $DNA$.

$A$ 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?

The different basic steps of genetic engineering are given below randomly:
$I.$ Identification of $DNA$ with desirable genes
$II.$ Gene transfer
$III.$ Maintenance of $DNA$ in host and gene cloning
$IV.$ Introduction of $DNA$ into host to form recombinant $DNA$
Which of the following represents the correct sequence of steps?