What is the function of ori in a vector?

Both (a) and (b)

a-Facilitate the replication of linked DNA

b-Regulate the copy number of the linked DNA 

c-Assist in selecting recombinants 

d-Both (a) and (b) is the correct option.

The origin of replication (ori) is a crucial element in a vector used in genetic engineering. It serves two essential functions:

1. Facilitating Replication: The ori sequence acts as a starting point for the replication of DNA within the host cells. When a DNA fragment is linked to the ori sequence in a vector, it gains the ability to replicate along with the host cell's DNA during cell division. This is essential to ensure that the inserted DNA is copied and passed on to daughter cells.
2. Controlling Copy Number: The ori sequence also plays a role in regulating the copy number of the linked DNA. Different vectors may have varying copy numbers, meaning they can exist in different quantities within the host cell. Some vectors, like plasmids with high-copy-number ori sequences, can produce many copies of the inserted DNA, resulting in a higher yield of the desired product. On the other hand, vectors with low-copy-number ori sequences produce fewer copies of the linked DNA.

By choosing an appropriate vector with the right ori sequence, scientists can control the number of copies of the target DNA they want to recover. This feature is essential when one needs a high yield of the recombinant DNA for further analysis or experimentation.