Assertion : A piece of DNA inserted into an alien organism generally does not replicate if not inserted into a chromosome.
Reason : Chromosomes have specific sequences called ori region where DNA replication is initiated.

Answer

A

Explanation

Origin of replication' is a sequence from where replication starts by binding of polymerase enzyme. An isolated piece of DNA without origin of replication or 'ori' site cannot replicate and is gradually6 lost during nuclear divisions. But if it is inserted within a chromosome it is replicated along with the chromosome as a result of the replication process initiated by the 'origin of replication' site of the chromosome. This is the reason why recombinant vectors used in genetic engineering must contain origin of replication so that they can replicate themselves during cell division in order to ensure presence of recombinant gene in all the progeny.