Cosmids are created by combining parts
   of the lambda chromosome with parts of plasmids.

   The cosmid pJB8 contains:
<LI> an  origin  of  replication (ori) that allows it to replicate as a
bacterial plasmid,
<LI> a cos gene for packing phage DNA into protein coats,
<LI> an ampicillin resistance gene (amp),
<LI> a  region  containing restriction sites for cloning (BamHI, EcoRI,
ClaI, and HindIII).

   Cosmids can carry up to 50 kb of inserted DNA.