Construction of recombinant DNA is as follows:
1. Desirable gene or DNA fragment from donor organism (bacteria, virus, plant or animal cells) is identified and isolated.
2. Vector DNA i.e. plasmid is also isolated from suitable bacteria. Plasmid is extra-chromosomal DNA in bacteria having marker gene such as antibiotic resistance gene.
3. Plasmid is then cut into fragments using restriction endonuclease.
4. DNA fragment from donor organism and plasmid are joined together by enzyme ligase giving rise to new DNA called as recombinant DNA (rDNA).
5. The recombinant DNA is now introduced into suitable host cells, for example Escherichia coli, Bacillus subtilis, etc.
6. Such transformed host cells are propagated on fresh medium so that millions of recombinant cells are formed with recombinant DNA.
