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by
Lynn Marmitt
Science education has metamorphosed from a strict content approach to one combining content and hands-on activity with the emphasis on hands on. Using the scientific method, students are taught to solve problems in an organized, methodical fashion. Viable research begins with observation/inquiry and proceeds to experimentation. It is through this process that scientists are able to address awaiting challenges in the areas of medicine and biology. This change will continue to motivate students and in turn begin the process of developing a scientifically literate population.
My unit, ”Brave New World,” will be used with seventh and eighth grade students as a supplement to the current curriculum. These two grades are divided into separate divisions of varying ability levels. The lessons developed can be modified to accommodate all students including the special education classes. This unit, consisting of a content/hands-on approach, will take about three to four weeks to complete and will be used along with the study of the cell and heredity.
“Brave New world” is divided into five sections. The first section, Genetics 101 begins with an introduction to cell structure and function, including detailed explanations of chromosomes, genes, inheritance and the work of Gregor Mendel. A student glossary will be included in this section.
Section two contains an introduction to an understanding of DNA. This begins with an explanation of the structure of DNA and the work of James Watson and Francis Crick.
After providing students with the basic concepts of genetics and an understanding of DNA structure, students will learn about the Human Genome project and the implications for future research. This section will prepare students for the portion of the unit, which deals with cloning.
The information presented next will include the history of cloning experimentation, how cloning is accomplished, why we clone and the future possibilities through its continued implementation.
Finally, student activities will examine the ethical implications of cloning and genetic engineering. Various case studies will be presented for analysis. This will tie the unit together and provide students with an opportunity to utilize decision-making and critical thinking skills through written activities.
Observations of microorganisms continued. In 1824 Dutrochet, a Frenchman, observed many different plants and animals and suggested, ”various parts of organisms are composed of cells”(2). This work was followed by Robert Brown, a Scottish scientist who in 1831 announced the central part of the cell is called the nucleus and by Dujardin, another Frenchman, whose discovery in 1835 enlightened scientists to the fact that cells are not hollow but are in fact filled with a thick, jellylike fluid.
Research continued by Matthew Schleiden in 1838 and Theodor Schwann in 1839. After observing plant and animal cells they concluded all plants and animals are composed of cells which are alive and which contribute to the total operation of the organism of which it is a part of. Rudolph Virchow confirmed their findings and in 1858 “he stated that all cells come from other living cells. The works of these scientists led to the formation of the cell theory which states that all living things are made of cells; cells are the basic units of structure and function and living cells come from other living cells” (3). This persistence, curiosity and observations laid the groundwork for future cellular research.
Most cells have similar characteristics. The outer covering of an animal cell is the cell membrane and the outer covering of a plant cell is the cell wall, inside which is the membrane. The membrane’s job is to provide protection and support for the cell. It also contains tiny openings, which control the amount of materials, which enter and leave the cell. Everything the cell needs or needs to get rid of must enter or leave here. The nucleus (which will be discussed in greater detail) is a large structure found in the center of the cell. This structure controls all of the cell’s activities. It also contains chemical substances that determine the inherited characteristics of the cell. The cytoplasm is the area of the cell between the cell membrane and the nucleus. Although jellylike and consisting of about 70% water it contains proteins, sugars, starches, fats, salts, vitamins and minerals which interact with each other. This is the site of metabolism and the site where organelles are stored. Within the cytoplasm lies the endoplasmic reticulum, which are tubular passageways serving as a transportation system for protein delivery. Ribosomes, which are found on the endoplasmic reticulum, are the protein making sites for RNA. Once the protein is made, it is then delivered to other cell parts via the endoplasmic reticulum. The golgi apparatus is where proteins made by ribosomes are delivered to needed areas. Other structures, which supply energy to the cell, are called mitochondria. These constructs break down sugars into water and carbon dioxide causing the release of energy. They are often called “the powerhouse of the cell” (5). Large fluid filled sacs also are floating in the cytoplasm. These storage bins for food and other materials are called vacuoles. Small structures called lysosomes contain enzymes, which help in the digestion of certain food molecules and the removal of undigested wastes.
The cell needs a number of different molecules to work efficiently. Nucleic acids DNA and RNA are the cell’s blueprints carrying all information for inheritance. Proteins serve as enzymes that run chemical reactions in cells. They are built from smaller molecules called amino acids. Carbohydrates provide the fuel supply for the cell. They include glucose, sucrose, fructose, starch and cellulose. Lipids, which are found in fats and oils, help the cell store energy for future use and are a major component of membranes.
Growth is one of the basic characteristics of all living things and cells begin to grow by reproducing and dividing. The process of producing new cells occurs during cell division. During this process one cell divides into two cells, which are called daughter cells, identical to the other and to the parent cell. This happens in a series of 6 phases. Phase one is called interphase. During the beginning of this phase, the cell is performing all functions except the division. This stage is where chromosomes are copied. Phase two, called prophase, is where mitosis begins. The nucleus divides into two nuclei and the formation of two new daughter cells begins. Phase three, metaphase, is the phase where chromosomes attach to a meshlike spindle at the center of the cell. Phase four, the point at which the chromosomes begin to separate is called anaphase. Phase five is the telophase stage. Here two new nuclei form and mitosis is completed. However cell division goes through a sixth phase called cytokinesis, which is the division of the cytoplasm and the formation of two new daughter cells.
As stated earlier, the nucleus is the control center of the cell and the site of the structures, which determine chemical characteristics. These structures, called chromosomes, are visible during the cell’s reproductive phase. Forty-six chromosomes are found in humans - 22 matched pairs and 2 sex chromosomes. Each chromosome is made up of either a single or double cord of DNA, deoxyribonucleic acid, the molecule containing the genetic instructions for making protein. Genes are located on the chromosomes. After cell division chromosomes are copied and passed on to offspring. The science, which studies how these traits are passed from parent to offspring, is called genetics.
Genetic material is composed of DNA and passed from one generation to the next. It is referred to as the “code of life” because it links generations together. After years of research scientists concluded that DNA “ is a large molecule that is built from a large number of similar building blocks”(6). It looks like a ladder with two sides and a number of rungs. The sides are twisted around each other with 10 rungs for each twist or turn. It is described as a double helix and in 1953 two biologists, James Watson and Francis Crick published their visual explanation of its appearance. Their explanation of this structure explained how DNA copies or replicates itself through cell division. During replication the two strands of DNA separate and synthesize a new complementary strand with the existing bases, sugars and phosphates. This process produces two new strands of DNA. Sometimes a mistake occurs during the replication process. This mistake makes a permanent change in the structure of the DNA and as a result of this, a mutation develops. Some mutations only have a minor effect, however some may have a major effect depending upon the way in which the protein is changed. These finding have led geneticists to probe into human disease through research and more. Using Watson and Crick’s explanation scientists were first able to begin unraveling the genetic code as a basis for future research.
DNA is made of three substances: Phosphate (P), a sugar called deoxyribose (D), and a third substance, which is a base. The first two substances make up the sides of the ladder. There are four differently shaped bases, which make up the rungs of the ladder: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T). A and G are “long” bases and T and C are “short” bases. A bases are always paired with T bases and C are always paired with G bases. The pairs of bases are held together by hydrogen bonds, but in order to stay bonded the base shapes have to fit together like puzzle pieces (6). The way in which the bases are sequenced makes up the DNA code. The cell uses this unique code to control protein synthesis, which determines our characteristics because many proteins are enzymes that control our biochemistry.
The project officially began in 1990 and became an international project when scientists from eighteen other countries got involved. They included Australia, Brazil, Canada, China, Denmark, European Union, France, Germany, Israel, Italy, Japan, Korea, Mexico, Netherlands, Russia, Sweden, United Kingdom and the United States. Their alliance formed the HUGO- Human Genome Organization. The United States Department of Energy led by Ari Patrios and the National Institute of Health led by Francis Collins along with scientists from various French agencies are at the helm of the research.
While reading the daily newspapers one can begin to understand the excitement generated by the project. Titles such as, “Scientists Plan: Map All DNA”, “Who Owns the Human Genome”, and “Genetic Questions are Sending Judges Back to the Classroom” are found on the front pages and beyond (7). The major goal of the project is to “produce a listing, base pair by base pair, of the entire human genetic code - all twenty-three chromosomes pairs with about three billion base pairs. The base by base survey is called sequencing and locating the genes along the DNA is called mapping” (8). This possible information uncovered through this process could help scientists understand and eventually cure genetic diseases.
“A genome is the sum total of genetic information in a living species” (9). The genetic information includes instructions for making proteins. Proteins are essential for all living things because they include instructions for how an organism looks, metabolize food and fight infections. “The code itself is a “series of codons” which is a sequence of three DNA bases” (10). The order of the bases is quite important. Sometimes there are abnormalities on DNA. These abnormalities are called mutations and are sometimes responsible for a number of diseases. Again, it is the hope of this project that scientists will be able to isolate disease-causing genes and suggest a therapy or treatment to correct them.
On April 6, 2000 an article in The New York Times reported that, “The Analysis of Human Genome is Said to be Completed.” The report, made by Dr. J Craig Venter stated that within a few weeks his company, Celera, would be able to identify the whole human genome. To actually assemble the whole thing it will take until 2003. Venter, one of the pioneers of the Human Genome Project reported that the genome belongs to a man because it has one X chromosome and one Y chromosome as opposed to the genome of a woman, which has two X chromosomes. The DNA in the study includes men and women of differing age and race. After it is put together it will be annotated, identifying all of the genes and their capabilities. Worried about the information gained from this and its potential Dr Venter said, “it would take a century to understand what each human gene does and that an attempt to alter the human germ line should not be made until then if ever” (11). Celera will use technology to attempt to find a faster way to sequence the DNA and expand the knowledge of genetics. The gene samples are from a variety of subjects who donated samples of blood cells and sperm cells. “This sampling works well because everyone has a unique DNA sequence but variations for 2 different genomes is said to be less than 1%” (12). The project has opened up enormous competition between the U.S Government and biotechnology companies.
Through the identification of genes and map-making capabilities of the human genome. “Recombinant DNA Technology allows researchers to snip out pieces of DNA and splice them into bacteria, where they can be grown, or cloned in large quantities”(13). Scientists use a variety of methods to copy genetic materials. “ A clone is a group of identical molecules, cells or organisms that are descended from a common ancestor through asexual reproduction” (14). In asexual reproduction, the offspring come from only one parent; so all cells contain the same genetic material. The members of a clone may be regarded as extensions of a single individual. Although cloning is not a new subject it has received a lot of negative publicity because of its comparison to science fiction. Scientific cloning has provided scientists with enormous capabilities for studying cancer, aging, genetic disorders and agriculture.
“Gene splicing is a method of cloning in which pieces of genes or whole genes are inserted into bacteria. The bacteria multiply and make large amounts of the protein called for by the newly inherited gene”(16). Dr. David Jackson pioneered gene splicing. His research with viral and bacterial cells provided scientists with tremendous capabilities in terms of genetically engineering specific host cells especially in his explanation of breaking DNA molecules into much smaller pieces. This contributed to a wide interest in how genetic materials of viruses can be turned on and off, making huge numbers of offspring. “The Recombinant DNA Technology allows researchers to simply snip out pieces of DNA, splice them into bacteria and clone them in huge quantities”(17). The fusion of the DNA samples is aided by plasmids. “Plasmids “are ring-shaped pieces of DNA and are the vehicles by which some bacteria inject some of their DNA directly into other bacteria when they mate in a process called conjugation” (18).
Plants also go through a cloning process. This type of cloning is done either naturally through stem cutting or by using laboratory methods. Using the lab methods scientists isolate single cells and provide appropriate conditions necessary for them to divide and form numerous cells that make up young plants. The method known as “tissue culture” uses hormones and certain growing conditions to produce clones (19).
Another method of cloning is through a process known as nuclear transfer. The nucleus of an egg cell is removed from a host animal and replaced with a cell nucleus from a different adult animal. Next the egg cell with the transferred nucleus is placed into the host animal’s reproductive system. This cell now has all of the capabilities needed to develop into an exact genetic replica. An experiment performed by John Gurdon in the early 1950’s used this process to clone the cells of tadpoles. Although the embryos never developed beyond the tadpole stage, this experiment illustrated that technology and perseverance would enable scientists to move forward in their research. In the 1970’s this technique was used to clone mice. Unsuccessful attempts at cloning followed until the research of Steen Willardon, an employee at the Granada Genetics, Inc. used the nuclear transfer method to produce calves from embryos. The embryos progressed to the 64 and 128-cell stage and confirmed the possibility of successful nuclear transfers in mammals (20).
Finally in 1995, Ian Wilmut, a Scottish scientist and his colleagues produced Megan and Morag, two live lambs whose embryos had been cultured for months in the laboratory. This set the stage a couple of years later when the world was introduced to Dolly, the first successfully cloned mammal. Dolly was cloned from a cell belonging to an adult animal. Cells were taken from the udder of a 6-year-old Finn Dorset ewe. These cells were cultured in a lab and then fused with unfertilized eggs from which the genetic material was removed. Two hundred and seventy-seven “reconstructed eggs” were cultured in temporary recipients. Twenty-nine eggs, which appeared to have developed normally, were implanted into thirteen surrogate Scottish Blackface ewes. One hundred and forty-eight days later, Dolly was born and later introduced to the world.
Bioethics ñ The study of ethical problems in genetics, medicine and agriculture raised by advances in biological research.
Cell- The basic unit of structure in a living thing.
Chromosome- Structure composed mostly of DNA located in the nucleus.
Clone- To make an exact copy of an organism.
DNA- Material inside cells those carries the genetic information. Scientific name: Deoxyribonucleic acid.
Dominant trait- Genetic trait which dominates or prevents the expression of the recessive trait.
Embryo- animal in the early stage of development before birth.
Genes- a segment of a chromosome that carries the genetic information for a single protein or trait.
Genetics- The study of genes and traits.
Genome- Complete set of instructions for making an organism.
Genotype- All the genes one carries; some are not always expressed.
Mitosis- Process in which the nucleus of a cell divides into two nuclei.
Mutation- A random change in the genetic material of an organism.
Nucleotides- Linear arrangement of a base attached to a sugar and a phosphate.
Phenotype- Physical expression of a gene.
Plasmid- A small piece of DNA from a prokaryotic cell that can be used to carry genes from one cell to another.
Prokaryotic- Cell which lacks a nuclear membrane such as bacteria.
Protein- Large molecule composed of amino acids.
Replication- Process by which any entity, such as DNA strands, are duplicated.
Students will design a three dimensional model of DNA to learn how nucleotides are formed.
MATERIALS:
Plastic straws, two different colors
Lucky Charms cereal (4 different colors)
Toothpicks
Yarn or string
PROCEDURE:
Pass out a set of materials to each student.
Using cereal to represent bases, assign each base a certain color - yellow/thymine, green/adenine, pink/cytosine and blue/guanine.
Pair and connect bases using toothpicks.
Cut straws into one-inch pieces and arrange by alternating color.
Connect the pieces of straw using the yarn or string.
Finally connect the cereal bases to the straw strands.
QUESTIONS:
Which bases pair together?
What is a code?
What do the pieces of cereal represent?
What do the pieces of straws represent?
What makes up the rungs of the ladder?
What makes up the sides of the ladder?
EXTENSION:
Using your individual model demonstrate the replication process.
Students will understand how to extract DNA from a given cell source.
MATERIALS:
Several plant tissues- broccoli, spinach, and onion
Blender
Warm water
Plastic container
Clear glass
Strainer or filter paper
Rubbing alcohol
Meat tenderizer, any variety
Liquid detergent
PROCEDURE:
Cut up small amount of plant tissue.
Put into blender.
Add warm water and blend until consistency is similar to thick soup.
After obtaining desired consistency, pour mixture through a strainer into a small plastic container.
Add 1/4-cup liquid detergent and 1-tablespoon meat tenderizer. Stir for about 5 minutes.
Empty 1/2 the mixture into a clear glass container.
Hold the container at a slightly tilted angle and slowly pour the alcohol down the side of the glass so that it forms a layer on top of the soap mixture.
Let it stand for about 5 minutes and you will observe white stringy stuff that rises to the top of the container.
Gather some DNA, slowly rotating it on a glass rod and observe it.
QUESTIONS:
What does the blender do?
Why is liquid detergent used in the experiment?
What does the meat tenderizer represent?
How come alcohol is used rather than water to extract the DNA?
Which part of the cell is the DNA located in?
Students will analyze a bioethical scenario and prepare a written presentation that explains their position.
MATERIALS:
Bioethical studies 1 and 2
PROCEDURE:
Assign one of the scenarios.
Students will read and analyze the scenario and will prepare a written presentation demonstrating their knowledge of basic genetics and bioethics.
SCENARIOS:
Research has confirmed that an inherited gene causes Sickle Cell Anemia. Recently Alice found out that her mother carried the gene. Alice’s oldest daughter Jane just got married and is considering starting a family. She needs to know if she is a carrier of the gene and thus needs some medical testing. Unfortunately her husband is unemployed and they lack insurance. Where does Jane go from here?
After the birth of their second child, Frank and Tina were very excited. While Tina was busy one morning the baby fell and broke his arm. After being rushed to the hospital and treated, life seemed to go on normally for the next couple of weeks. During the baby’s routine arm check-up, x-rays revealed that the bones were completely healed. Doctors were so confused by this amazing recovery that they began to perform a series of tests on the child.
After extensive testing the doctors discovered that the baby had a rare gene that gives him the power to heal broken bones at a rate confusing to man. Immediately the doctors get so excited. They approach Frank and Tina with this amazing news and ask their permission to extract some of the baby’s DNA so that the gene can be cloned. News like this travels very fast and reporters and several biotechnology companies bombard Frank and Tina. The companies are offering 5 million dollars for DNA samples. What should Frank and Tina do?
QUESTIONS:
What is the dilemma?
What are the facts?
What are arguments for and against?
- What are your views on the issue?
Who will be affected by the decisions reached?
What ethical problems does the decision seem to raise?
Bryan, Jenny. Genetic Engineering. New York: Thomson Learning, 1995.
Cohen, Daniel. Cloning. Brookfield: Millbrook Press, 1998.
Edelson, Edward. Francis Crick and James Watson and the Building Blocks of Life. New York: Oxford University Press, 1998.
Gutnik, Martin J. Genetics - Projects for Young Scientists. New York: Franklin Watts, 1985
Lampton, Christopher. DNA and the Creation of New Life. New York: Arco Publishing, 1983.
Stwertha, Eve and Albert. Genetic Engineering. New York: Franklin Watts, 1982.
Swisher, Clarice. Genetic Engineering. San Diego: Lucent Books, 1996.
Yount, Lisa. Genetics and Genetic Engineering. New York: Facts on File, 1997.
Baskin, Yvonne. The Gene Doctors. New York: William Morrow and Company, 1984.
Bender, David L. and Bruno Leone, ed. Ethics. San Diego: Greenhaven Press, 1995.
Fitzgerald, Karen. “Cloning: Entering the Clone Age.” Science World, February 2, 1994.
Hopkins, Patrick D. “Bad Copies: How Popular Media Represents Cloning as an Ethical Problem.” Hastings Center Report,
Hyde, Margaret O. and Lawrence E. Hyde. Cloning and the New Genetics. Hillside: Enslow Publishers, Inc., 1984.
Madigan, Timothy J. and others. “Cloning Humans.” Free Inquiry, Summer, 1997.
Ravage, Barbara. “Medical Genetics: A Brave New World.” Current Health 2, February 1993.
Rorvik, David. In His Image: The Cloning of a Man. Philadelphia: J.B. Lippincott Company, 1978.
Silver, Lee M. Remaking Eden: Cloning and Beyond in a Brave New World. New York: Avon Books, 1997.
Suzuki, David and Peter Knudtson. Genethics. Cambridge: Harvard University Press, 1989.
Wilcox, Frank. DNA The Thread of Life. Minneapolis: Lerner Publication Company, 1980.
@EN:FOOTNOTES 1. Linda Densman and Linda Grant & et al, Cells: Building Blocks of Life (Upper Saddle River: Prentice Hall, 1997), 44.
2. Raymond F. Oram, Biology: Living Systems, 2nd. ed. (Columbus: Charles E. Merrill Publishing Company, 1976), 62.
3. Oram, 65.
4. Oram, 67.
5. Densman, 53.
6. Edward Edelson, Francis Crick and James Watson and the Building Blocks of Life (New York: Oxford University Press, 1998), 57.
7. Robert M. Hazen and James Trefil, Science Matters - Achieving Scientific Literacy (New York: Anchor Books, 1991), 240.
8. “The Struggle to Decipher Human Genes,” New York Times, March 10, 1998: 32.
9. Hazen, 242.
10. Edelson, 96.
11. Edelson, 78.
12. “Analysis of Human Genome is Said to be Completed,” New York Times, April 7, 2000: 1.
13. “Human Genome Project”, Encarta Encyclopedia, http://encarta.msn.com/ index/conciseindex/AC/0AC83000.ht?z=1&pg=2&br=1.
14. Beverly Merz, The Human Genome Project, http://www.hhmi.org/ genetictrail/reading/read.htm, 1-3.
15. Margaret O. and Lawrence E. Hyde, Cloning and the New Genetics (Hillside: Enslow Publishers, Inc., 1984), 13.
16. Hyde, 90.
17. Hazen, 239.
18. Hyde, 48.
19. Hyde, 48.
20. Hyde, 85.
21. Hyde, 18.
Contents of 2000 Volume VII | Directory of Volumes | Index | Yale-New Haven Teachers Institute
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