Genetic Engineering

Genes, as we know are unique set of instructions which decide how all the living things (including the non-living Virus) develop, grow and live. These instructions are found inside the cells on Chromosomes. Chromosome is divided into small stretches of deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) that control different aspects of the organism’s growth and traits. Thus, gene is the molecular unit of heredity of a living organism. The number of genes varies from organism to organism and increases with complexity of the organisms.

Mutational Breeding

On genetic level, there are two ways to achieve desired traits. One of them is to introduce heritable changes into the DNA of one parent using mutations. For this, the agents used are called mutagens. Mutagens can be various chemicals or various types of radiations. This type of breeding is known as “mutation breeding”. There are more than two thousand Mutagenic plants currently. One of India’s high yield varieties of wheat called “Sharbati Sonora” was produced via Mutation Breeding only. However, the basic problem with mutation breeding is that the mutagens introduce random changes in the plant’s DNA the results are far more unpredictable than changes brought about by specific genetic modification. Thus, mutation breeding also remains haphazard and unpredictable.

Jumping Genes

For plant breeders, there is a highly assisting phenomenon that the DNA is inherently plastic and not a static molecule. It can undergo considerable natural rearrangements. These rearrangements are caused by the regions of DNA which jump around an organism’s genome. These regions are called transposons or jumping genes. The more the fraction of jumping genes, the more is the variability and plasticity of genome of a particular organism. This jumping of genes occurs naturally also. For instance, if a piece of such DNA jumps into a gene that is involved in the biosynthesis of chlorophyll, the offspring may lack normal biosynthesis of Chlorophyll resulting in the variegation of the foliation leaves. Eventually, the jumping genes were first discovered in maize plants.

Horizontal Transfer and Vertical Transfer of Genes

Other natural phenomena that have assisted the plant breeders are horizontal & vertical transfers of genes. The vertical transfer of genes is what happens when genes are passed from parents to offsprings. Horizontal gene transfer is the movement of genetic information between sexually unrelated organisms. While vertical gene transfer is the basis of life of all living things, horizontal transfers have occurred naturally rarely. One example of Horizontal gene transfer is the Bacterium that causes TB (Tuberculosis). This TB Bacteria called Mycobacterium tuberculosis carries a chunk of human DNA too.

Transgenic Organisms

The traditional plant / animal breeding have resulted in the development of wide variety of flora and fauna, yet as we discussed above, it is a tardy hit-or-miss process. The Genetic engineering allows the scientists to transfer specific genes into organisms, thus enabling them to introduce ONLY the desired traits. The plants and animals such produced are called transgenic plants and animals.

One of the advantages of genetic modification is that genes can be taken from any organism and thus it allows horizontal transfer of genes. Such horizontal transfer of genes would not be possible by natural breeding. Many of the insect resistant crops, herbicide tolerant crops, and crops with other desirable traits have been produced by such horizontal transfer of genes. One popular example is the Golden Rice, a variety of common rice produced through genetic engineering to biosynthesize beta-carotene, a precursor of vitamin A, in the edible parts of rice. To ‘create’ Golden rice, two genes were horizontally transferred into the plants viz. psy from daffodil and crtI from soil bacterium Erwinia uredovora.

Bt Toxin

Bacillus thuringiensis is a naturally occurring soil bacterium. This bacterium produces some proteins which are called Bt proteins. These Bt proteins are toxic to certain insects (not all); so also called Bt toxins. There are around 50 verities of such Bt Toxins identified. Some of the Bt toxins target the larval forms of butterflies and moths, while others target flies and mosquitoes. Some others target beetles. They cause either little or no harm to other organisms such as people and other flora / fauna. For decades, such toxins have been used in the conventional and organic agriculture. In fact, Bt toxins have been considered environmentally friendly alternatives to the broad-spectrum insecticides sprays, which target all insects.

The problem with the insecticide sprays is that they are sprayed on plants and they can kill only those insects which are exposed to sprays. They cannot harm the pests which burrow into plant tissues and are not exposed to sprays. The use of Bt genes was based upon this premise that it will produce the toxin deep within the plant itself and thus plant would automatically become insect resistant. This trait was successfully achieved in Maize, cotton and some other crops. The Bt gene was successfully transferred and thus produced transgenic maize plants were resistant to corn borer, corn earworm etc. while the cotton plants were resistant to Cotton bollworm and Pink bollworm.

Transgenesis versus Cisgenesis

Cisgenesis is the genetic modification of a recipient plant with a natural gene from a crossable—sexually compatible—plant. This means that Horizontal transfer of genes in related organism (for example one domesticated and another wild) is Cisgenesis. On the other hand, Transgenesis is the genetic modification via horizontal transfer of genes from unrelated and / or sexually incompatible with the recipient organism. For example, Bt crops have the Bt toxin producing gene from a bacterium.

GMO versus LMO

The genetic material of GMO was altered using genetic engineering techniques. LMO is a term used in Cartagena Protocol of Biosafety. The definition of LMO uses two terms viz. living and modern biotechnology. This implies that LMOs include living organisms which have been modified either by genetic engineering or by any other tool of modern biotechnology. Thus All GMOs are LMOs but all LMOs are not GMOs. For instance, organisms produced by the fusion of cells from different taxonomic families are products of modern biotechnology but not genetic technology. Such organism would fall in LMO but not in GMO.