Transgenic plants and animals have been genetically altered in a laboratory to have traits and characteristics they don't normally have on their own. Trangenesis can be useful in agriculture, medicine and industry.
The milk from transgenic cows is currently being used in biomedical research.
Methodology
One of the methods scientists use to create live animal transgenic offspring is to microinject the DNA of one animal into the nucleus of a reproductive cell of another animal of the same or a different species. The manipulated cell is cultured in vitro in a lab to the embryonic stage then transferred to a recipient female where it is nurtured and born live. Scientists also use retroviruses (a virus that is unable to replicate on its own) to move genetic material into a host cell. Once the host cell has developed to twenty times its normal size, it is then transferred into the animal that now carries the new genetic material in its DNA. In a third method, totipotent stem cells (very early stem cells that can develop into any kind of specialized cell) are isolated from a particular embryo, microinjected with a desired gene from a separate animal or species and then re-inserted into the host embryo. This embryo then becomes a genetically altered adult. This last method, unlike the other two that require live offspring for genetic testing, allows testing for the altered genes at the cellular level.
Botanists have genetically modified crops for years through cross-pollination. By isolating and cloning a specific gene characteristic, botanists can introduce the DNA of one plant into the nucleus of other plants. These transgenic plants will then replicate the cloned DNA through normal pollination. Scientists are also currently using a species of soil-dwelling bacteria to carry the cloned DNA into the host plant. This bacterium, called agrobacterium tumefaciens, if left on its own will normally infect plant cells with its own DNA, causing crown gall disease. When scientifically altered, A. tumefaciens will transfer the cloned DNA into the host plant, which then becomes transgenic.
Significance
According to the Department of Soil and Crop Sciences at Colorado State University, transgenic corn, soybeans, cotton, canola, potatoes, squash and papaya are currently being farmed worldwide, with the majority of the crops (74.8 million acres) planted in the U.S. The products of hybrid crops are currently in the marketplace in this country. Transgenic crops have been altered to be more resistant to broad-spectrum herbicides and specific insects and pests.
Scientists are presently using transgenic animals to understand the role of specific genes in illness and to develop more effective treatments for genetic diseases. They are also being used to test the safety of new medicines and vaccines.
Benefits
By growing herbicide-resistant crops, a farmer can use a single herbicide at all growth stages, allowing the chemicals to break down quickly in soil and reducing the environmental impact of said chemicals. Insect-resistant hybrid crops also decreasing the amount of insecticides used in the field and improve environmental quality. Farmers who reduce the amount of chemicals used in their fields also reap financial benefits.
In their paper "The Role of Transgenic Animals in Biomedical Research" (2001-2009), Glaxo-Smith-Kline Pharmaceuticals, Inc. states that their scientists have chemically engineered mice with a higher glucose clearance rate that are currently being used in obesity studies.
Scientists have also genetically improved the size of the livestock, producing cows that produce more milk, sheep that grow more wool, and pigs and cattle with more meat on them.
Potential
Transgenic animals are being developed to provide new organs for transplantation into humans. Transgenic pigs with genes compatible with humans have been bred in hopes that the human recipient will not reject their livers, kidneys and hearts. Scientists are presently working to remove a pig protein that causes donor rejection and makes this operation impossible at this time. Research is underway to breed transgenic sheep that produce a protein in their milk that treats a rare, genetic pancreatic disorder. Scientists are using milk from transgenic cows in research for the treatment of cystic fibrosis and hereditary emphysema, and in the production of insulin, growth hormone and anti-clotting factors in blood.
Considerations
By using transgenic mice in biomedical research, scientists can reduce and ultimately eliminate the use of dogs and primates, including chimpanzees and monkeys, for experimentation. According to researchers at the American Institute of Biological Sciences, other ethical considerations include whether there should be universal standards for transgenesis, whether the welfare of all life forms (not only human) should be considered, and whether scientists should use laboratory transgenic methods for research only and not use live transgenic animals.
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