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Unraveling the Code of Life-A Historical Perspective of the Genetic Revolution

Joan Carlson

Since life began on earth, approximately 4.6 billion years ago, DNA (deoxyribonucleic acid) has served as the genetic blueprint which dictated the cellular metabolic activities critical for survival. Although the term "gene" was not used until the 1900's, research which led to the discovery of gene function began in the 1800's. Gregor Mendel, an Austrian monk worked for years in his monastery's garden, cross-breeding different varieties of pea plants. Keeping careful records, Mendel counted the offspring of his crosses, looking at the phenotypic expression of genes, such as the height of plants, the colors of the flowers, and the shape of the peas. Careful observation, accurate record keeping, and critical analysis of data led Mendel to theorize the existence of "factors" or hereditary units which were passed to offspring by the male and female parents of each plant. Mendel died in 1884, having received no public recognition of the value of his work. Mendel's factors were indeed genes, yet his research and discoveries went unnoticed until early in the 1900's.

During the same time period, from 1809 to 1882 Englishman Charles Darwin, the grandson of a noted physician and naturalist, Erasmus Darwin, was gathering information which would lead to significant advances in the biological sciences. Darwin studied medicine and then theology. After earning a degree from Cambridge, and still unsure about his career goals, Darwin set out in 1831 on a five year British expedition on the H.M.S. Beagle. Darwin, in his role as a naturalist, studied plants and animals at each site, collecting specimens and drawing sketches of many of the living things he found. He is most famous for his work on the Galapagos Islands off the coast of South America.

Darwin also collected fossils, and found evidence of extinct animals which resembled present day species. He also noticed that on each island he visited, species showed variation in traits. In finches for example, beak shape, and beak length allowed Darwin to distinguish species from their counterparts on other islands, and from similar species on the mainland of South America.

Darwin was also a careful observer, collector, and analyzer of data. His studies and careful review of different specimens collected prompted him to theorize that modern species had evolved from earlier species. Darwin also theorized that a selective process occurred in nature in which the organisms with the most favorable characteristics would be the most likely to survive. The initial response to Darwin's work was somewhat negative, especially from religious leaders who were upset because Darwin's theories challenged the accepted Biblical interpretation of how life formed on earth. Darwin and Mendel's work would have a major impact on biological theories of genetics and evolution.

Since the rediscovery of Mendel's work in the early 1900's, there has been an incredible explosion of information concerning the nature of the gene. Biologists have unraveled the mystery of the importance of the nucleus and the chromosomes within the nucleus. Since the observations that chromosomes are visible during cell division and that the number of chromosomes is cut in half during meiosis to form egg and sperm, there have been unceasing efforts to understand how molecules of DNA are translated to produce the variety of organisms which inhabit the earth. American James Watson and Englishman Francis Crick, with the assistance of a number of other research biologists, were able to analyze data and postulate the double helix structure of DNA in 1953. The concept that DNA is the universal language of life, possessed by cells of bacteria, protists, fungi, plants, and animals links all organisms which inhabit the earth.

The recognition of this common bond between living organisms led to the development of the science of modern biotechnology and genetic engineering. Engineering technology uses living organisms or parts of organisms to create and modify products to improve plants or animals. Since the 1970's, when biologists figured out how to cut DNA from one organism and place that DNA into another organism, recombinant DNA technology has made valuable contributions to medicine by providing useful drugs such as insulin, human growth hormone, interferon, and TPA(tissue plasminogen activator). Human gene therapy, which involves replacing genes in individuals who lack specific genes or whose genes are defective has been attempted as well.

The relatively new science of reproductive technology has focused on scientifically aided assistance to increase reproductive probability. Doctors interested in human reproductive technology have moved from in vitro (in laboratory glassware) fertilization, to storing frozen human embryos for later implantation. Surrogate mother's carrying embryos who are not their own genetic offspring is a reality. In 1993, Dr. Robert Stillman and Jerry Hall, working at George Washington University cloned human embryos, (forty eight clones in all), some of which were allowed to grow for six days before termination of their research experiment. Cloning, or the production of genetically identical organisms was first accomplished with carrots. In this cloning procedure, one cell from the root of the carrot is used to generate an entire new plant. After scientists perfected plant cloning procedures, they moved from the carrot to clone frogs in 1952. By 1970, scientists had cloned mice and by 1973 they had cloned cows . Sheep cloning followed in 1979. The opportunities for farmers to produce herds of cows with superior milk production, or for horse breeders to produce superior stock horses by cloning was seen as a major technological advance, certain to be of benefit to mankind. Advances in biotechnology by gene manipulation to benefit the farming industry have proven effective in the production of certain pest-resistant and frost-resistant crops, as well as hardier and more productive livestock. A genetically altered tomato species has been approved for sale in the United States. The tomato has been genetically altered to delay ripening for a longer shelf life in the market.

The strong interest in human genes continues to grow. In 1990, the United States government launched a concentrated effort. The Human Genome Initiative, is attempting to map the location of all human genes. The estimated cost of this project is over two hundred million dollars per year. It is targeted for completion in the year 2005. The DNA codes for many diseases, including cystic fibrosis, sickle cell anemia and Huntington's chorea, have been found and their location on specific chromosomes has already been established.

The rapid evolution of the field of biotechnology is not without controversy. Scientific debate continues on the moral and ethical questions which arise with each new discovery. As citizens, we are obligated to be knowledgeable about the field of modern Genetics. As the code of life is deciphered and man manipulates life at the molecular level, it is important that citizens be aware of the potential and perils which accompany technological advances in the field of biology.

A number of critical issues need to be considered as we proceed to manipulate the code of life. An overview of the history of genetics with your students and the opportunity to introduce them to activities and labs to acquaint them with current topics in biotechnology will clarify some of the biological principles which are the foundation of this technology and alert them to ethical and moral issues which are associated with gene manipulation.

Some of the following questions may serve to stimulate class discussions:
  • How safe is recombinant DNA research as we genetically engineer crops to withstand frost and insect pests or add genes for enzymes which prevent fruit from spoiling too fast?

  • Will these genetically engineered crops be safe for consumption? If herbicide resistance is built into crops will the farmer use more herbicide to get rid of the weeds, and thereby threaten ground water drinking supplies?

  • How should we care for frozen human embryos? What about parent's who decide that they have enough children and have frozen human embryos which remain? What if parents die and their embryos remain in freezers ?

  • Will there come a time when we can select which genes will be found in our offspring once all genes are identified by the Human Genome Project?

  • Will employers discriminate against us based on our genetic make-up which might show a predisposition to Alzheimer's disease or cancer or alcoholism? Should our genetic make-up be considered personal information and be protected by Constitutional rights?

  • How are we applying what we learn in terms of genetic technology? How are we to control genetic technology? Who will be the decision makers? What research needs to be held in check until ethical issues are studied? Will there be abuse and exploitation of the new technology?

The questions above and those that you and your students generate will provide opportunities for students to develop a strong knowledge base and to understand the significant effects that genetic technology will have on their future.



Bibliography

Elmer-Dewitt, Philip. Nov. 8,1993. Cloning: Where Do We Draw The Line?. Time Vol. 142, No.19

Lewis,Ricki . 1994. Human Genetics . William C. Brown Publishers

Micklos, David A. 1990. DNA Science . Carolina Biological Supply Company, Cold Spring Harbor Press.

Sattelle, David. 1988. Biotechnology in Perspective. Industrial Biotechnology Association , Hobsons Publishing.




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