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Examples of Genetic Engineering

By Eric Yang

Transgenic Plants

Transgenic plants are being made to introduce new traits of DNA into themselves using modern DNA technology.

The genetic manipulation of plants has been going on since the dawn of agriculture, but until recently the process was slow and tedious of cross-breeding varieties. but now by using Genetic engineering, it promises to speed the process and broaden the varitities of what could the plant become.

using Gentics engineering the transgenic plant have a number of different advantages over the normal plants

Improved Nutritional Quality

An emerging major use of genetic engineering for crops is to alter the quality of the crop. Fresh fruits and vegetables begin to deteriorate immediately after being harvested. Delaying or preventing this deterioration not only preserves a produce's flavor, and appearance, but maintains the nutritional value of the produce. Genes that change the hormonal status of the harvested crops are the major targets for genetic engineering toward longer shelf-life.

Disease Resistance

Genetic engineering also has been used in the battle against weeds. Bacterial genes allow crops to either degrade herbicides or be resistant to them. The herbicides that are used are generally very effective, killing most plants. They are considered environmentally benign, degrading rapidly in the soil and having little impact on humans or other organisms. Thus a whole field of transgenic crops can be sprayed with broad-spectrum herbicides, killing all plants except the crops. Corn, soybeans, canola, and cotton that have been engineered to withstand either insects or herbicides, or both, are widely planted in some countries, including the United States. In addition, other crops, including potatoes, tomatoes, tropical fruits, and melons, have been engineered for resistance to viral diseases.

Insect Resistance

The major use of plant genetic engineering has been to make crops easier to grow by decreasing the impact of pests. Insect resistance has been achieved by transforming a crop using a Bt gene. Bt genes were isolated from Bacillus thuringiensis, a common soil bacterium. They code for proteins that severely disrupt the digestive system of insects. Thus an insect eating the leaf of a plant expressing a Bt gene stops eating and dies of starvation. There are many Bt genes, each of which targets a particular group of insects. Some Bt genes, for example, target caterpillars. Others target beetles.

Genetic Engineering in medince

The production of insulin

For many years, insulin was obtained by purifying it from the pancreas of cows and pigs slaughtered for food. This was expensive, difficult and the insulin could cause allergic reactions.

Once the structure of human insulin had been found, in 1955, the cow and pig insulin could be chemically modified to be the same as human insulin. It is now made by genetically-engineered microbes. They produce human insulin in a pure form that is less likely to cause allergic reactions.

Human insulin is produced in a very controlled and clean environment.

Genetically-engineered bacteria are grown in large stainless steel fermentation vessels. The vessel contains all the nutrients needed for growth.

When the fermentation is complete, the mixture containing the bacteria is harvested. The bacteria are filtered off and broken open to release the insulin they have produced. It is then purified and packaged into bottles for distribution.

All the equipment is kept sterile so that contamination cannot get into the medicine. Regular checks make sure that all the processes are working properly and the insulin meets the required quality.

Steps to produre insulin

Insert gene for human insulin into bacteria

Clean fermentation vessel and add solution containing nutrients

Put genetically-engineered bacteria into fermentation vessels

Allow genetically-engineered bacteria to grow

Harvest bacteria and break open to release insulin

Purify and package human insulin

Transgenic Animials

The term transgenic animal refers to an animal in which there has been a deliberate modification of the genome, Foreign DNA is introduced into the animal, using recombinant DNA technology, and then must be transmitted through the germ line so that every cell, including germ cells, of the animal contain the same modified genetic material.

The methods to create transgenic animal

DNA microinjection

This method involves the direct microinjection of a chosen gene construct (a single gene or a combination of genes) from another member of the same species or from a different species, into the pronucleus of a fertilized ovum. It is one of the first methods that proved to be effective in mammals (Gordon and Ruddle, 1981). The introduced DNA may lead to the over- or under-expression of certain genes or to the expression of genes entirely new to the animal species. The insertion of DNA is, however, a random process, and there is a high probability that the introduced gene will not insert itself into a site on the host DNA that will permit its expression. The manipulated fertilized ovum is transferred into the oviduct of a recipient female, or foster mother that has been induced to act as a recipient by mating with a vasectomized male.

A major advantage of this method is its applicability to a wide variety of species.

Retrovirus-mediated gene transfer.

To increase the probability of expression, gene transfer is mediated by means of a carrier or vector, generally a virus or a plasmid. Retroviruses are commonly used as vectors to transfer genetic material into the cell, taking advantage of their ability to infect host cells in this way. Offspring derived from this method are chimeric, i.e., not all cells carry the retrovirus. Transmission of the transgene is possible only if the retrovirus integrates into some of the germ cells.

For any of these techniques the success rate in terms of live birth of animals containing the transgene is extremely low. Providing that the genetic manipulation does not lead to abortion, the result is a first generation (F1) of animals that need to be tested for the expression of the transgene. Depending on the technique used, the F1 generation may result in chimeras. When the transgene has integrated into the germ cells, the so-called germ line chimeras are then inbred for 10 to 20 generations until homozygous transgenic animals are obtained and the transgene is present in every cell. At this stage embryos carrying the transgene can be frozen and stored for subsequent implantation.

Embryonic stem cell-mediated gene transfer.

This method involves prior insertion of the desired DNA sequence by homologous recombination into an in vitro culture of embryonic stem (ES) cells. Stem cells are undifferentiated cells that have the potential to differentiate into any type of cell (somatic and germ cells) and therefore to give rise to a complete organism. These cells are then incorporated into an embryo at the blastocyst stage of development. The result is a chimeric animal. ES cell-mediated gene transfer is the method of choice for gene inactivation, the so-called knock-out method.

This technique is of particular importance for the study of the genetic control of developmental processes. This technique works particularly well in mice. It has the advantage of allowing precise targeting of defined mutations in the gene via homologous recombination.

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one leaf is from a Transgenic plant and the other one is from a normal plant

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