. Describe the following terms


(i) Phage Vectors

(ii) Cosmids

(iii) YAC Vectors

(iv) BAC Vectors

(v) Shuttle Vectors

 

Best Answer

(i) Phage Vectors

Phages are undoubtedly an excellent vector for carrying larger genes at a time (20-25 kb long genes or cluster of genes). Phage DNA is packed in proteinaceous head region and is linear and double stranded. It is nearly 50 kb long and can carry foreign DNA of approximately 25 kb length.

(ii) Cosmids

Cosmids have been constructed by combining certain features of plasmid and the ‘cos’ sites of phage lambda. (Collins and Bruning, 1978; Collins and Hohn, 1979). They have been constructed to add some of the advantages of phage vectors to the plasmid vectors’ the cos sites endeavour in vitro packaging system to the plasmid vector. The cosmid vectors, however, provide an efficient means of cloning large fragments of foreign DNA (32-48 kb of foreign DNA).

(iii) YAC Vectors

YACs or Yeast artificial chromosomes are being used as vectors to clone DNA fragments of more than 2500 Mb in size. They are being highly used in mapping larger genomes like Human Genome Project.

(iv) BAC Vectors

BACs or Bacterial artificial chromosomes are used as vectors which are based on natural extra-chromosomal plasmid of E. coli, the fertility or F-plasmid. This vector bears genes for replication and maintenance of F-factor, a selectable marker and cloning sites.

(v) Shuttle Vectors

They are the plasmids capable of shuttling genes between two organisms. One of the organism is prokaryote like E. coli and other is a eukaryote like yeast. Such vectors should bear unique origins of replication for every cell type. They should have separate markers for transformed host cells harboring the vector.

 

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