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especially useful for the analysis of highly complex genomes and are an important

part of various genome mapping projects (Section 6.9).

The upper limit of the insert capacity of phagelis approximately 21 kb. This is

because of the requirement for essential genes and the fact that the maximum length

Antibiotic

resistance gene

Cosmid cossites

Restriction site

Foreign DNA to be cloned

Digest cosmid and foreign DNA with same restriction enzyme

Ligation

(fragments inserted randomly between cosmids)

Packagingin vitro only if cos–cos distance is in range 37 to 52 kb

Infection by phage of E. coli

(selection for antibiotic resistant colonies)

DNA recircularises via

cos sites and replicates

as a plasmid within E. coli

E. coli bacterium

Chromosomal DNA

Recombinant cosmid

Fig. 6.23Scheme for cloning foreign DNA fragments in cosmid vectors.

219 6.3 Cloning vectors