BOTANY Higher Secondary Second Year - Textbooks Online

DNA fragments of donor and vector are joined together. This
process is called splicing. As a result of splicing hybrid DNA
or recombinant DNA (rDNA) is obtained.
4. The rDNA is introduced into the host cells such as E.coli,
Bacillus subtilis, Streptomyces sp. etc.,
5. For this the host cells are treated with the enzyme cellulase. So
that the cell wall of host becomes permeable to the entry of
rDNA.
The host organism follows the instructions of “foreign rDNA”.
It continues to multiply with the foreign DNA or gene of interest.
After a short time, this results in a colony of bacteria having rDNA
fragments. Each colony is grown separately to obtain multiplication of
rDNA fragments. At the end we get a number of colonies having
identical copies of rDNA fragments. This is called molecular coloning
or gene coloning.
Once the gene for the production of human insulin from
pancreatic cells is introduced into E.coli, the recipient cell produces
human insulin. This is the way by which the human insulin is made to
be produced by bacterial cell such as E.coli.
Gene transfer in plants
Agrobacterium tumefaciens is a soil inhabiting bacterium and has Ti
(tumor inducing) plasmid. This bacterium invades crops such as tomato,
sunflower, brinjal and cotton and causes crown gall disease which is in the
form of tumerous growth. The Ti plasmid carried by the pathogenic
bacterium causes tumours. For effective cloning of foreign genes by the
plant cells, and for introduction of genes into plant system, Agrobacterium
strains are modified by the removal of tumour – inducing genes from the
bacterium. T–DNA is the part of Ti plasmid transferred into plant cell
DNA. The T–DNA which holds the desired foreign gene after splicing is
introduced into the plant cell. The bacterial plasmid do not produce
tumerous growth since the gene had been deleted. Once the T–DNA
along with the spliced gene is introduced, it combines with the chromosome
of the donor cell where it produces copies of itself, by migrating from one
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