Cosmid

A synthetic plasmid which incorporates the cos ends, and one or more selectable markers such as an antibiotic resistance gene. Cosmids were designed as vectors able to incorporate DNA fragments up to 40-50 kb in size.

Artificially constructed cloning vector containing the cos gene of phage lambda. Cosmids can be packaged in lambda phage particles for infection into E. coli; this permits cloning of larger DNA fragments (up to 45kb) than can be introduced into bacterial hosts in plasmid vectors.