Regents Prep: Living Environment: Heredity & Genetics:
Genetic Engineering

Selective Breeding
For thousands of years new varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits.  Some selective breeding techniques include
artificial selection, where individuals with desirable traits are mated to produce offspring with those traits.   A variation of this process traditionally used in agriculture is inbreeding, where the offspring produced by artificial selection are mated with one another to reinforce those desirable traits.   Hybridization is a special case of selective breeding.   This involves crossing two individuals with different desirable traits to produce offspring with a combination of both desirable traits.   An example of this are Santa Gertrudis cattle, which were developed by breeding English shorthorn cattle, which provided for good beef, but lacked heat resistance, with Brahman cattle from India which were highly resistant to heat and humidity.  The Santa Gertrudis breed of cattle has excellent beef, and thrives in hot, humid environments.

An Example of Selective Breeding

Brahman cattle:
Good resistance to heat but poor beef.

English shorthorn cattle: Good beef but poor heat resistance.

Santa Gertrudis cattle: Formed by crossing Brahman and English shorthorns; has good heat resistance and beef.

Genetic Engineering
In recent years new varieties of farm plants and animals have been engineered by manipulating their genetic instructions to produce new characteristics.  This technology is known as genetic engineering or recombinant DNA technology.  Different enzymes can be used to cut, copy (clone), and move segments of DNA.   An important category of enzyme used to cut a section of a gene and its DNA from an organism is known as a restriction enzyme.  When this piece of DNA, which has been cut out of one organism, is placed in another organism, that section of gene will express the characteristics that were expressed by this gene in the organism it was taken from..

An Example of Genetic Engineering

Knowledge of genetics, including genetic engineering, is making possible new fields of health care.  Genetic engineering is being used to engineer many new types of more efficient plants and animals, as well as provide chemicals needed for human health care.   It may be possible to use aspect of genetic engineering to correct some human health defects.  Some examples of chemicals being mass produced by human genes in bacteria include insulin, human growth hormone, and interferon. Substances from genetically engineered organisms have reduced the cost and side effects of replacing missing human body chemicals.  While genetic engineering technology has many practical benefits, its use has also raised many legitimate ethical concerns.

Other Genetic Technologies
Cloning involves producing a group of genetically identical offspring from the cells of an organism.  This technique may greatly increase agricultural productivity.  Plants and animals with desirable qualities can be rapidly produced from the cells of a single organism.

Genetic mapping, which is the location of specific genes inside the chromosomes of cells makes it possible to detect, and perhaps in the future correct defective genes that may lead to poor health.  The human genome project has involved the mapping of the major genes influencing human traits, thus allowing humans to know the basic framework of their genetic code

Knowledge of genetics is making possible new fields of health care.  Genetic mapping in combination with genetic engineering and other genetic technologies may make it possible to correct defective genes that may lead to poor health.   

There are many ethical concerns to these advanced genetic technologies, including possible problems associated with the cloning of humans.  Another down side to genetic mapping technologies it is possible that some organizations may use this genetic information against individuals.


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