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The advent of genetic engineering, also called rDT, started in 1952 with the discovery of Hershey and Chase, stating DNA as the genetic material (Hershey and Chase, 1952). Cohen and Boyer in the early 1970s were the first to show that the genetic material of one organism can be easily expressed in the other. Genetic engineering (Figure 1.1), in general, is the process in which the DNA is extracted, modified, transformed into a host cell, and a new organism is formed. The DNA from the desired organism is extracted and purified. It is then cleaved using restriction enzymes to get the gene of interest from it. The DNA fragment is then ligated into a vector, which acts as a driving vehicle for the DNA molecule to the host cells. This chimeric DNA molecule is then transformed into the host cells, and selection procedure under suitable stress conditions takes place. Finally, after numerous generations, the organism growing in the stress conditions is said to be recombinant or genetically modified. Genetic engineering has emerged as a crucial step in the development of industrial bioprocesses.

Each and every organism has a different genetic (DNA) makeup, which in turn makes the whole organism different with respect to their carbohydrates, lipids, and proteins. This is due to the fact that DNA transcribes and translates to mRNA and proteins, respectively (central dogma). This makes DNA the choice for manipulation in genetic engineering as manipulating it leads to the generation of a whole new organism. This postulation gives rise to many other disciplines of genetic engineering like recombinant protein production, protein engineering, metabolic engineering, etc.

Every organism being different makes it difficult to use proteins and other biomolecules of one organism to the other. This was the main reason why proteins/enzymes from animals cannot be used by humans. Earlier, insulin was extracted from the pancreas of slaughtered pigs, posing a threat to human health. This leads to the discovery of the first recombinant product, Insulin, approved by the US Food and Drug Administration (FDA) in 1982 (Goeddel et al., 1979). Now synthetic insulin is easily being produced by yeast worldwide as Escherichia coli does not perform post‐translational modifications required to form functional insulin.

Similarly, genetic engineering is now used to produce several other biocommodities. Modifying DNA and getting it expressed inside the host organism requires several steps, as shown in Figure 1.1 and the number of enzymes. These enzymes are explained in further sections with other requirements for genetic engineering.