Question

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.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

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 gradually 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.