The application of biotechnology to agriculturally important crop species is an age old practice and has traditionally evolved the use of selective breeding to bring about an exchange of genetic material between two parent plants to produce offspring having desired traits such as increased yields, disease resistance, and enhanced product quality. Observation was the key factor. From decades the crop varieties that were chosen for domestication have been gradually modified by selecting individual plants that grew the best and produced the best grains, vegetables, and fruits. This selective breeding has reached a level almost where the present crop has very little similarities when compared to its first parent. Modern corn is derived from a wild Central American grass plant called Teosinte. The present corn plant shares very few similarities with the wild Teosinte. This concept was still a debate until the molecular studies proved that a particular species of Teosinte is the corn progenitor.
The exchange of genetic material through conventional breeding requires that the two plants being crossed (bred) are of the same, or closely related, species as in the case of corn, it was the successive breeding of the selective cultivars of the same species lead to such a large variation. Active plant breeding measures have increased the chances of genetic variation when compared to possible chance of cross breeding in the wild due to random mating. Application of genetic engineering in the field of agriculture has eliminated the barriers in breeding plants. It is now possible to move genes among life forms as diverse as bacteria, tomatoes or sheep. A large spectrum of technologies has now made it possible to alter the heritable traits under in vitro conditions and later reintroduce those traits to get a better product. This is advantageous when minor changes in DNA can provide the desired change. Methods have been developed to selectively alter the genetic instructions in the DNA that direct the growth and development of living organisms by recombinant DNA (rDNA) technology. In this technology Primarily identify the desired gene DNA through screening techniques and isolate it from the plant cell, the respective gene is excised from the genome and later the gene is ligated or attached to a vector. Vector is particle which can cross species barrier and introduce the gene. Later the vector molecule with the desired interest gene is re introduced to the cell lacking the trait of interest . Since DNA is chemically identical among all organisms, the instructions on these cloned pieces of DNA can be readily exchanged and "understood" between organisms as dissimilar as bacteria and humans. The unique character introduced will act as the marker to select those cells which has successfully accepted the new gene. Such cells are further cultured to get the transgenic plants. These new varieties are called transgenic because they require the recombination of genetic materials from different organisms to cause the desired change. There is always a possibility that the added gene gets integrated in random position thus altering posing challenges, but such phenomenon did happen in conventional breeding techniques and the site targeted fusion is now eliminating such possibilities.
It is not always a gene necessary that a gene needs to be transfer the only way to cross the species barrier. The other sophisticated breeding techniques as protoplast fusion and embryo rescue, which results in fusion of cells from sexually incompatible plants in a laboratory and over-come their natural inability to produce offspring. Techniques for genetic modification aids in hybridization of plants of the same species, different species, and even different genera. "Wide crosses" of plants from different species or genera allow scientists to add into an existing crop species traits for disease and pest resistance, increased yield, or different nutritional qualities. They can even be used to create entirely new plant species. Examples of such artificial wide crosses include a wheat-barley hybrid, a tomato-potato hybrid, and a radish-rapeseed hybrid. Some of the genes introduced aiming at obtaining Insect resistant Viral resistant plants will require farmer to spray very little pesticides.
But genetic engineering technology has its own challenges to overcome as in the unknown adverse effects it can cause over the time which is also the reason for the ethical issue being raised continuously.
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