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Definition of Cosmid
Medically reviewed by Dr. Otari Nergadze, Neurosurgeon | Updated: January 2026
Cosmid: DNA from a bacterial virus into which is spliced a small fragment of a genome to be amplified and sequenced. A cosmid is an artificially constructed structure. It is used in cloning (copying) pieces of DNA.
(On a technical level, a cosmid contains the cos gene of phage lambda and can be packaged in a lambda phage particle for infection into E. coli, permitting cloning of larger DNA fragments that can be introduced into bacterial hosts in plasmid vectors).