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

Explants before organogenesis, is

$A$ : Some nations are developing laws to prevent unauthorised exploiation of their bioresources and traditional knowledge.
$R$ : Brazzein, a protein obtained from West African plant, was isolated, sequenced and patented in $U.S.A.$

Rennin used in cheese industry is

Which one of the following vectors is used to replace the defective gene in gene therapy ?