A) Ri plasmid
B) lambda phage
C) pBR 322
D) Ti plasmid
Correct Answer: D
Solution :
Plasmids are extra chromosomal, closed, circular double stranded molecules of DNA present in most eukaryotes. All plasmids carry replicon pieces of DNA that have the genetic information required to replicate. Ti (Tumour inducing) plasmid has genes for the production of tumours. Ti-plasmid is found in Agrobacreriuin tumefadens which produces crown gall (tumour) in a large number of dicot species. A. tumefadens is a Gram-negative soil bacterium that infects a wide range of plants and causes crown galls. Ti-plasmid contains T-region and vir-region. T-region is transferred into the host genome, generally called T-DNA and vir-region is virulence region. T-DNA has four genes, two genes iaaM and iaaH govern the synthesis of IAA, one gene ipt determines the production of cytokinin and the remaining gene OS, is concerned with opine. The genes iaaM, iaaH and ipt are involved in tumour production and are usually called oncogenes, these genes have to be removed from the T-DNA of a Ti-plasmid before it can be used as a vector.
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