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The following points highlight the top six applications of recombinant DNA technology. The applications are: 1. Medical Diagnosis of Disease 2. Gene Therapy 3. Production of Vaccines through rDNA Technology 4. Cloning 5. Genetically Modified Crops 6. Sustainable Agriculture.
Application # 1. Medical Diagnosis of Disease:
rDNA technology acts as a tool to diagnose the diseases. This involves the construction of probes (short, single strands of radioactive or fluorescent DNA, used to identify the complementary DNA). These probes are used to identify the infectious agents, such as Salmonella (food poisoning), Staphylococcus (pus), HIV, hepatitis virus, etc. With the help of this technique the infected child can also be identified. This can be done by testing the DNA of prospective parents for any genetic disorder, i.e. they are not carrier of a disorder.
Few examples of this technique are as follows:
a. Phenylketonuria:
In this, phenylalanine fails to get converted into tyrosine. This causes disturbances in metabolism resulting in mental retardation. It is possible to cure this disease by using rDNA technique in early periods of pregnancy.
b. Thalassemia Genes:
In this, syntheses of alpha and beta globin chains are reduced and the excess chains precipitate and cause haemolytic anaemia and spleen enlargement. Human globin genes have been identified and sequenced. Alpha and beta globin genes are closely linked. Human globin gene has also been developed and cloned. Still lot of work needs to be done to cure this disease.
c. Haemophilia Gene:
It is a sex linked disease in human where blood clotting does not take place normally due to the absence of clotting factor VIII C. By using gene cloning technique, the clotting factor VIII C gene was cloned to express in mammalian cell lines and produce the protein VIII C responsible for blood clotting.
Application # 2. Gene Therapy:
Gene therapy means to change a faulty gene with a normal, healthy gene. Gene therapy can be used to correct a rare disease, like sickle cell anemia, which is caused by single mutation and killer diseases such as Severe Combined Immuno Deficiency (SCID). Gene therapy is used to produce recombinant therapeutic bio chemicals such as insulin, somatotropin, somatostatin, interferon, human blood clotting factor VIII, etc.
Several protocols have been developed for expression and introduction of genes in humans, but the clinical efficiency has to be demonstrated conclusively. Success of gene therapy is dependent on the development of better gene transfer vector for sustained, long-term expression of foreign gene as well as better understanding of gene physiology of human disease.
There are two gene transfer strategies:
a. The in vivo approach which involves introduction of genes directly into the target organ of an individual. This is done in patients, therefore called as patient therapy.
b. Ex vivo approach where the cells are isolated for gene transfer in vitro followed by transplantation of genetically modified cells back into the patients.
Application # 3. Production of Vaccines through rDNA Technology:
Human Insulin:
For this the gene of interest is picked up from a human cell. Plasmid from E. coli is taken and by using restriction enzyme it is cut to create sticky ends. Now the gene of interest (insulin gene) and plasmid are joined by DNA ligase. This is now known as rDNA. This rDNA is now inserted in the plasmid free E.coli. Multiplication of rDNA starts growth in medium. Clones of genetically engineered bacteria are used to extract recombinant insulin.
In the same way by using hepatitis B virus and Agrobacterium tumefaciens, hepatitis B vaccine and edible vaccine can be generated. (Fig. 2).
Application # 4. Cloning:
Cloning means to create a carbon copy or identical copy of single parent. This word is related to only the living world and not to non-living world, where we can find thousands of copies of one object like number of photocopies of the same document. In nature asexually reproducing organisms produce clones.
For example, amoeba reproducing by binary fission produce two daughter amoebae which are clones. In human beings, monozygotic, identical twins are clones. They are the result of separation of the two cells of zygote which are in double cell stage. The most famous example of cloning is Dolly sheep.
1. Microbial Cloning:
Once the microbial cells are modified or genetically altered they are cloned on a growth medium. In a few days there are millions of clones generated. Each one is the copy of a single parent. Table 2 shows the genetically modified microbes and their applications.
2. Cell Cloning:
This technique is based on the fact that certain cells are totipotent, i.e. they are not differentiated. This phenomenon is seen both in plants and animals. When seen in plants it is called totipotency and when seen in animals it is known as pluriopotency. Almost all the plants show totipotency, whereas in animals pluriopotency is seen in fertilised egg and stem cells in blastocyst. Cells showing pluriopotency can be differentiated into nerve cells, kidney cells and even heart cells.
3. Plant Cloning:
The growth areas of plant, i.e. root and shoot tip are used in plant cloning. This is used to multiply those plants which are agronomically (crop plants) important. Plants which are useful to horticulturist (orchids, gladiolies, etc.) are multiplied at a very fast pace.
By gene manipulation we can have drought, disease, insect and pest resistant varieties. We can also have herbicide tolerant variety. Genetically modified food can also be produced like Vitamin A rich rice (Golden Rice), Lysin rich pulse, etc.
Application # 5. Genetically Modified Crops:
A crop which bears a foreign gene of desired function of other organism and expresses itself is called genetically modified crop (GM crop) or transgenic crop. In the last 20 years, considerable progress has been made on isolation, characterisation and introduction of novel genes into plants. In the year 2002, transgenic plants were cultivated on around 587 million hectare land in the world.
The number of farmers involved in this was 5.5 million. Transgenic crop plants have many beneficial traits such as pest and insect resistance, weed control, improved oil quality, herbicide tolerance, delayed fruit ripening, etc.
Two main advantages of transgenic crops are:
a. Any gene can be transferred from any organism
b. Change in genotype can be controlled as only the desired gene is introduced.
In contrary to this, when conventional method like hybridisation is used only those genes can be used which are found in such species and along with desirable change undesirable genes are also added.
The effects of introduction of foreign gene of interest are as follows:
a. Existing biosynthetic pathway gets modified so that a new end product is obtained.
b. It produces a protein that is the product of interest.
c. It produces a protein that on its own produce the desired phenotype.
d. It prevents the expression of an already existing gene.
Application # 6. Sustainable Agriculture:
Human population is ever increasing and because of this the major challenge for agricultural scientists is to increase the food production at almost the same pace. This is not possible by the conventional methods used for increasing and improving the yield. In recent years, it has been understood that biotechnology can play a major role to overcome this problem.
Earlier emphasis was laid on the use of pesticides and fertilisers. Later it was realised that use of pesticides and fertilisers led to environmental pollution. Due to this reason such practices cannot be continued for indefinite period of time. The only way to overcome this is to switch over to sustainable agriculture.
Sustainable agriculture means to use the resources in judicious manner where we do not exploit it to support the present requirement and take care to leave behind sufficient resources for the coming generation. Care should also be taken to use renewable resources. Development which minimises the use of non-renewable resources results in minimising the environmental exploitation.
Through genetic manipulation crop production and usefulness of the products can be increased. Due to the introduction of agricultural biotechnology we have plants which have not one but many improved traits. The only problem which is faced while commercialising these varieties is that with the passage of time their expression is reduced.
To overcome this problem scientists cross different transgenic lines that have improved breeding material. The progeny so formed undergoes selfing to give rise to varieties which have desired characters. By the above technique we can have traits that are all of same size, colour, weight and shape. Their nutritional value can also be improved keeping intact their time of ripening.