Cosmid 〈REAL〉

Today, although superseded by BACs for many applications due to the latter’s even larger capacity (100–350 kb) and lower recombination rates, cosmids remain useful for targeted cloning, subcloning of large gene clusters, and functional studies in microbial genetics.

A cosmid is essentially a small, high-copy-number plasmid that has been engineered to contain one critical element from the lambda phage—the . This 200-base-pair sequence is the only phage component retained; cosmids lack all other lambda genes required for viral packaging, replication, or lysis. cosmid

In the field of molecular cloning, the cosmid represents a powerful hybrid vector that bridges the gap between standard plasmids and bacteriophage lambda (λ) systems. Developed in the late 1970s, cosmids were designed to address a key limitation of traditional plasmid vectors: their inability to efficiently clone DNA fragments larger than 10–15 kilobases (kb). Today, although superseded by BACs for many applications