Biology · Principles and Processes in Biotechnology

Which of the following characteristics is most essential for a cloning vector to facilitate high copy number of the linked DNA in host cells?

1. Presence of unique restriction sites for multiple antibiotic resistance genes
2. An origin of replication (ori) that supports high copy number
3. Presence of \( \beta \)-galactosidase coding sequence for insertional inactivation
4. A selectable marker that encodes resistance to chloramphenicol only