(i) The living cells from which the genetic material is to be obtained has to be broken open. One popular method is to shear the cells in a blender and treat them with a suitable detergent. (ii) The genetic material from the cell is to be removed. Several techniques are available to remove the DNA. The DNA molecules can even be spooled on to a glass rod. The glass rod bearing the DNA molecules is then lifted up from the debris of the cells.
(iii) The next step is to cut away the specific genes of interest from the DNA molecule. Restriction enzymes popularly called molecular scissors are used to cut and separate the desired gene from the DNA helix. (iv) In the next step the specific sections of DNA are incorporated into cloning vectors or vehicles such as plasmids, phages etc. These cloning vehicles are then introduced into a rapidly multiplying living system such as bacteria where multiple copies of the cloned DNA can be obtained. The cloned DNA also called chimeric DNA contains the desired foreign gene.
The cloned DNA is also called recombinant DNA. (v) In the final step which is a very delicate process the cloned gene is allowed to express itself in the bacterial cell. Gene expression here means production of a desired gene product. For instance if a human insulin gene is cloned in a plasmid and is inserted into a bacterial cell, the bacterial cell along with its metabolic products also will produce insulin This insulin may then be separated by the normal methods of chemical purification and isolation.