Animal Biotechnology

COSMIDS

• Cosmids are extrachromosomal circular DNA molecules that combine features of plasmids and phages. They also have a high transformation efficiency, and their cloning limit of 35-50 kb is larger than that of plasmids or phages.
• The cosmid vector is a combination of the plasmid vector and the COS site of lambda phage which allows the target DNA to be inserted into the lambda head. 
• It has the following advantages:
  • High transformation efficiency.
  • The cosmid vector can carry up to 45 kb whereas plasmid and lambda phage vectors are limited to 25 kb.