Every protein or enzyme in the body is coded by a gene. Genes are responsible for controlling a particular trait or function in the body. They pass on the hereditary information from generations to generations; more precisely they are responsible for the genotypic and phenotypic characteristics of an individual. Scientifically, genetic engineering is the manipulation or alteration in the genetic makeup of an organism to impart certain characters to it. It is an artificial process which uses the recombinant DNA technology and is a bit different from the natural breeding techniques. The organisms produced, thus, are referred to as genetically modified organisms (GMO's) or transgenic organisms. This technique is related to other biotechnological fields like animal and human cloning.
Genetic engineering has had wide applications in almost all fields related to biotechnology where the genome of the organism is involved. The process of transfer of genetic material from one organism to another using a vector or a carrier is referred to as transformation. All the experiments to produce a therapeutic compound or an organism have been performed on bacteria, crops, and many animals mostly mice, as human experimentation has not been possible due to obvious reasons.
Direct Methods of Transformation
Microinjection, macroinjection, bombardment techniques/biolistics, electroporation, liposome mediated transformation, and transformation using chemicals like silicon carbide fibers.
Indirect Methods of Transformation
Vector based transformation; vectors include bacterial plasmids (Agrobacterium mediated transfer), lamba phage, and bacteriophage (phage particles are highly efficient in transformation).
Genetic Engineering in Humans
In humans, the technique remains the same but involves human genes to change the existing phenotype. Genetic manipulation has been performed to modify certain mutagenic or disease coding genes, to treat some genetic disorders, apart from producing drugs and vaccines. It has also been used to increase the longevity, and immunity of an organism and more precisely to study the gene expression. Manipulation of the genetic material of the humans is of 2 types; somatic, where the somatic cells are transformed, and germline, where the transformation is performed in the egg cell or the sperm cell.
Since, in the former technique the transformation is in the somatic cells of the body, it is not heritable. The first almost successful trial of genetic manipulation was performed on people affected by severe combined immunodeficiency (SCID), in 1990. This trail showed positive results as it gave people functional immunity which they were deprived of earlier. Other modifications in human genetics are on low priority since the success rate has been doubtful.
Isolating the Gene
Selection of the desired gene and its isolation is a prerequisite to start the process. The desired gene is isolated and multiplied using the PCR (polymerase chain reaction) technique. Alternatively, it might be a part of the genomic library (libraries containing fragments of DNA of one particular genome), from where it can be copied, synthesized, and then inserted in the DNA.
The gene that is isolated needs to be checked for expression. Hence, every gene is made up of a promoter, selectable marker gene, and terminator. The promoter region is responsible for transcription of the gene and it is terminated on reaching the terminator region. The selectable marker gene confers antibiotic resistance to the whole construct, that helps to distinguish transformed cells from the non-transformed cells. However, the gene cannot enter the host on its own, therefore it has to be combined with a vector. This process is carried out using restriction digestion enzymes, ligation enzymes and molecular cloning using polymerases.
Bacteria have been widely used to take up the gene or the foreign DNA with help of the aforementioned transformation methods. After integration, the gene or the DNA replicates using the host replication system and produces many copies of itself.
Selection and Confirmation
It is possible to differentiate the transformed cells from the non-transformed ones by growing them in the presence of the antibiotic coded by the selectable marker gene. Another method is to use DNA probe complementary to the inserted gene which will specifically bind to the gene of interest and can be traced and confirmed using DNA mapping, electrophoretic techniques, like Southern blotting, and Bioassays.
The benefits of genetic engineering are evident in the fields of agriculture, environment, and food production. Having said that, since it is a field which involves a lot of research, it's obvious for it to have its share of negative effects.
- Many genetic disorders, complications like diabetes, cystic fibrosis, etc. have been cured by this technique. It involves removal of faulty genes and modifying cells to produce the desired trait by gene therapy. Insulin and human growth hormones are the best examples of molecules obtained by genetic manipulation. Here the gene's coding for these hormones are transformed in bacterial cells on a large scale to elevate the hormone production.
- Animal cloning and transformation has been exclusively done on mice. The first successfully transformed animal was Dolly, a cloned sheep. However, the ethical issues have been a major hindrance as far as research is concerned.
- Genetic engineering has been used to produce pest and disease resistant plants. This technique is also used to increase the nutritive value of the plants. The best example is Bt cotton plants where Bacillus thureingiensis (a bacterium) has been used to insert various pest and disease resistant genes in the crops.
- Genetically modified foods have helped people with high amounts of nutrition. The golden rice, and the flavor savor tomatoes are the best examples of such foods.
- Since genetic engineering involves severe experimentation, there are high possibilities for the genes to produce undesirable mutations and traits leading to allergies in crops that hamper its nutritional value. The resultant traits might give rise to new pathogens that are harmful to the entire ecosystem.
- This technique requires insertion of the desired gene at the exact location for which great skill is required, especially when it involves many risk factors. Also, transformation of a single gene is difficult, since it codes for multiple traits.
- Genetic engineering is an expensive technique to carry out. It requires skilled manpower, excellent and accurate devices and chemicals, and highly sophisticated laboratories.
- Lastly, one cannot ignore the ethics and debatable issues which are involved in the use of animals and plants for manipulation which are supposed to be "God's creation".
This field contributes to immense amounts of research that has started-off long back, but is continued and will always continue as long as biotechnology exists.