Genetic Engineering

Definition:
Genetic engineering, recombinant DNA technology, genetic modification/manipulation and gene splicing are terms that apply to the direct manipulation of an organism's genes. Genetic engineering is different from traditional breeding, where the organism's genes are manipulated indirectly. Genetic engineering uses the techniques of molecular cloning and transformation to alter the structure and characteristics of genes directly
Introduction:
Genetic engineering is a laboratory technique used by scientists to change the DNA of living organisms.
DNA is the blueprint for the individuality of an organism. The organism relies upon the information stored in its DNA for the management of every biochemical process. The life, growth and unique features of the organism depend on its DNA. The segments of DNA which have been associated with specific features or functions of an organism are called genes.

Molecular biologists have discovered many enzymes which change the structure of DNA in living organisms. Some of these enzymes can cut and join strands of DNA. Using such enzymes, scientists learned to cut specific genes from DNA and to build customized DNA using these genes. They also learned about vectors, strands of DNA such as viruses, which can infect a cell and insert themselves into its DNA.

With this knowledge, scientists started to build vectors which incorporated genes of their choosing and used the new vectors to insert these genes into the DNA of living organisms. Genetic engineers believe they can improve the foods we eat by doing this. For example, tomatoes are sensitive to frost. This shortens their growing season. Fish, on the other hand, survive in very cold water. Scientists identified a particular gene which enables a flounder to resist cold and used the technology of genetic engineering to insert this 'anti-freeze' gene into a tomato. This makes it possible to extend the growing season of the tomato.

Ways through which Genetic Engineering Accomplishes:
There are a number of ways through which genetic engineering is accomplished. Essentially, the process has five main steps

1. Isolation of the genes of interest
2. Insertion of the genes into a transfer vector
3. Transfer of the vector to the organism to be modified
4. Transformation of the cells of the organism
5. Selection of the genetically modified organism (GMO) from those that have not been successfully modified

Isolation is achieved by identifying the gene of interest that the scientist wishes to insert into the organism, usually using existing knowledge of the various functions of genes. DNA information can be obtained from cDNA or gDNA libraries, and amplified using PCR techniques. If necessary, i.e. for insertion of eukaryotic genomic DNA into prokaryotes, further modification may be carried out such as removal of introns or ligating prokaryotic promoters.

Insertion of a gene into a vector such as a plasmid can be done once the gene of interest is isolated. Other vectors can also be used, such as viral vectors, bacterial conjugation, liposomes, or even direct insertion using a gene gun. Restriction enzymes and ligases are of great use in this crucial step if it is being inserted into prokaryotic or viral vectors. Daniel Nathans and Hamilton Smith received the 1978 Nobel Prize in Physiology or Medicine for their isolation of restriction endonucleases.

Once the vector is obtained, it can be used to transform the target organism. Depending on the vector used, it can be complex or simple. For example, using raw DNA with gene guns is a fairly straightforward process but with low success rates, where the DNA is coated with molecules such as gold and fired directly into a cell. Other more complex methods, such as bacterial transformation or using viruses as vectors have higher success rates.

After transformation, the GMO can be selected from those that have failed to take up the vector in various ways. One method is screening with DNA probes that can stick to the gene of interest that was supposed to have been transplanted. Another is to package genes conferring resistance to certain chemicals such as antibiotics or herbicides into the vector. This chemical is then applied ensuring that only those cells that have taken up the vector will survive.