Why is a vector required for cloning of a gene?
A vector is required for gene cloning because it forms an essential component of the two-component system along with a compatible host. The vector provides essential sequences required for its replication in the host organism, while the host supplies the necessary enzymes and proteins for replication.
Additionally, the vector must have an origin of replication (ori) that enables it to replicate autonomously inside the host. It should be small in size for easy incorporation into the host cell and must possess unique restriction sites for inserting the gene. The vector also requires selectable markers (such as antibiotic resistance genes) to screen out transformants and identify successful recombinants.
Explanation
The textbook clearly establishes that gene cloning is a two-component system requiring both a compatible host and a vector. The context explains that the vector's primary function is to provide essential sequences for replication within the host. Key features mentioned include: origin of replication for autonomous replication, small size for easy host incorporation, unique restriction sites for gene insertion, and selectable markers for screening transformants. These points directly answer why a vector is indispensable for cloning.