Unraveling the Code of Life-A Historical Perspective of the Genetic Revolution
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
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:
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.
- 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
- 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
- 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?
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.