Cosmid.net May 2026

Cosmids were first developed in the 1970s as a means to clone larger DNA fragments than those manageable with traditional plasmid vectors. They are essentially plasmids that have been engineered to carry a cos site, a specific DNA sequence derived from the bacteriophage lambda. This cos site allows cosmids to be packaged in lambda phage particles in vitro, enabling the cloning of DNA fragments up to 40-50 kilobases (kb) in size. This capability is particularly valuable for constructing genomic libraries, where large segments of genomic DNA need to be represented.