Assertion (A): Origin of replication is an essential part of a vector.

Reason (R): Ori is responsible for initiating replication.

Both Assertion (A) and Reason (R) are correct and R is the correct explanation of A.

The correct answer is Option (1) -Both Assertion (A) and Reason (R) are correct, and R is the correct explanation of A.

Explanation:

• Assertion (A): "Origin of replication is an essential part of a vector" is correct because the origin of replication (ori) is a sequence in the vector that allows the DNA to replicate independently within a host cell.
• Reason (R): "Ori is responsible for initiating replication" is also correct. The ori sequence is crucial because it signals the machinery within the host cell to start replicating the vector DNA. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA it should be cloned in a vector whose origin support high copy number. Without the ori, the vector (such as a plasmid) would not be able to replicate, and the genetic material it carries wouldn't be passed on to daughter cells during cell division.

Thus, the reason accurately explains why the assertion is true.