In this article we will discuss about:- 1. Definition of Recombinant DNA 2. History of Recombinant DNA 3. Milestones.
Definition of Recombinant DNA:
For centuries humans have been altering the genetic makeup of organisms by selective breeding of plant and animals. The deliberate modification in genetic material of an organism by changing the nucleic acid directly is called genetic engineering or gene cloning or gene manipulation and is accomplished by several methods which are collectively known as recombinant DNA (rDNA) technology.
Recombinant DNA technology begins a new area of research and applied aspects of biology. Therefore, it is a part of biotechnology which is gaining momentum and much boost in recent years.
In breeding programmes much work has been done on alteration of nucleotides by several para-sexual or conjugation methods in different group of organisms. Now-a-day, a large number of mutagenic agents are available that mutate the genes. It is likely that the changed genes may be beneficial, neutral or lethal.
Moreover, the conventional breeding programmes are time taking to ensure that the genes have been altered. In contrast, the rDNA technology has solved several problems which hardly or never are possible through the conventional methods.
Gene cloning or genetic engineering can be defined as “changing of genes by using in vitro processes”. A unified definition of genetic engineering has been given by Smith (1996) as the formation of new combinations of heritable material by the insertion of nucleic acid molecules produced by whatever means outside the cell, into any virus, bacterial plasmid or other vector system so as to allow their incorporation into a host organism in which they do not naturally occur but in which they are capable of continued propagation.
In brief, gene technology is the modification of the genetic properties of an organism by using rDNA technology. Genes are like the biological software filled with programmes that govern the growth, development and function of organism. By changing in programme of the software it is possible to bring about alteration in the characters of a given organism.
A gene of known function can be isolated from its normal location by biochemical methods in vitro. Moreover, a gene can be synthesized by using gene machine.
The isolated genes can be transferred into the microbial cells (that of course do not contain) via a suitable vector. The transfened gene replicates normally and is handed over to the next progeny over generations. After confirmation for its presence through biochemical procedures clone of the same cell is produced.
History of Recombinant DNA:
The first break through of rDNA technology occurred with the discovery of restriction endonucleases (restriction enzyme) during the late 1960s by Werner, Arber and Hamilton Smith. The restriction enzymes were discovered in microorganisms. These enzymes protect the host cell from the bacteriophage. The restriction enzymes are described in the preceding section.
In 1969, Herbert Boyer isolated restriction enzyme EcoRI from E. coli that cleaves the DNA between G and A in the base sequence GAATTC as below:
In 1970 Howard Temin and Davin Baltimore independently discovered the enzyme reverse transcriptase from retroviruses. Later on this enzyme was used to construct a DNA called complementary DNA (cDNA) from any mRNA (see Fig. 6.10).
In, 1972 David Jackson, Robert Symons and Paul Berg successfully generated rDNA molecules. They allowed the stickly ends of complementary DNA by using an enzyme DNA ligase.
In 1973 for the first time S.Cohen and H. Boyer developed a recombinant plasmid (pSC101) which after using as vector replicated well within a bacterial host. In, 1975, Edwin M.Southern developed a method for detection of specific DNA fragments for isolation of a gene from complex mixture of DNA. This method is known as the Southern blotting technique.
Milestones of Recombinant DNA:
Some milestones of recombinant DNA technology have been summarized as below:
1976 – First prenatal diagnosis by using gene specific probe.
1977 – Methods for rapid DNA sequencing, discovery of split genes and somatostanin by rDNA.
1979 – Insulin synthesized by using rDNA; first human viral antigen.
1981 – Foot and mouth disease viral antigen cloned.
1982 – Commercial production of coli of genetically engineered human insulin, Isolation, cloning and characterization of human cancer gene.
1983 – Engineered Ti-plasmid used to transform plants.
1985 – Insertion of cloned gene from Salmonella into tobacco plant to make resistant to herbicide glyphosphate; Development of PCR technique.
1986 – Development of gene gun.
1989 – First field test of genetically engineered virus (baculovirus) that kills cabbage looper caterpillars.
1990 – Production of first transformed com.
1991 – Production of first transgenic pigs and goats, manufacture of human haemoglobin, first test of gene therapy on human cancer patients.
1994 – The Flavr Savr tomato introduced; the first genetically engineered whole food approved for sale. Fully human monoclonal antibodies produced in genetically engineered mice.
1997 – World’s first mammalian clone (Dolly) developed from a non-reproductive cell of an adult animal through cloning by nuclear transplantation.