Cosmid

Cosmids are a form of plasmids which can hold roughly double the amount of DNA that a regular plasmid can . A hybrid of bacterial plasmids and a bacteriophage, the name 'cosmids' is derived from the cos sites, that they contain in their Lambda phage region, which are crucial in the packaging process. The cos sites also allow them to form what is known as cohesive ends, much like sticky ends, which allow the cosmid to ligate back after foreign DNA is inserted into it. The functional uses of these cosmids is primarily for genetic manipulation, such as creating genomic libraries, therefore allowing us to sequence organisms.