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Chapter 1 Mapping the Human Genome |
by Donna M. Brinton, Christine Holten, and Jodi L. Nooyen
Background | Classroom Applications | Internet Resources | Appendices
Background
DNA, deoxyribonucleic acid, is the most important molecule ever discovered because it is the key to how all living things pass their traits on to the next generation. The search for DNA, specifically human DNA, has been selected as the topic of this first chapter because of what this discovery means for biology, medicine, law, and ethics.
Some of the questions this chapter explores include:
- What is DNA?
- What was the chain of discoveries that finally led scientists to their current understanding of DNA?
- How advanced is our current understanding of human DNA?
- What is the human genome project?
- What effects on society will the mapping of the
human genome have?
Rather than focus on the scientific details of this discovery, this chapter gives an overview of the important concepts related to DNA's initial discovery and later research conducted in this field. Teachers can use the lesson plans and materials to help students understand these fundamental concepts and gain a command of the vocabulary necessary to discuss them.
Background Information
It is a well-known fact that we inherit physical traits from our parents. If a child is left-handed, it is very likely that one of her parents writes with his or her left hand. If a boy's father is bald, he will have a greater chance of going bald when he gets older. While everyone knew that physical traits were inherited, it wasn't until the twentieth century that scientists discovered the biological key to this process: DNA, or deoxyribonucleic acid. Finding DNA took almost 100 years.
Now scientists are working to decode the DNA molecule. To do this, they must "read" each of the over 3 billion DNA letters in the human body. This decoding of human DNA, also known as the human genome project, will result in a map of the DNA in the human body. As former U.S. President Clinton said, "Without a doubt, this is the most important, most wondrous map ever produced by humankind."
From 1866 to the present, many scientists have learned important things about how genes work. Below is a review of the important developments in DNA research.
| 1866 | Gregor Mendel, an Austrian monk, described basic elements of heredity (these are now called genes). |
| 1860's | Friedrich Miescher, a Swiss chemist, did research on the chemical composition of white blood cells. He discovered two types of molecules in the nucleus of the blood cells—ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). |
| 1870-1900 | There were no major findings during this period. Scientists knew that DNA played some part in heredity, but its structure seemed too simple to play a major role. During this period, scientists thought that proteins (with their much more complex structure) played the most important role in heredity. |
1902 |
At Columbia University in New York City, a medical student began to study whether chromosomes were made up of genes and if all cells in the body contained these genes. |
| 1920's | Frederick Griffith, an English physician, accidentally discovered a transforming factor while doing experiments with bacteria. When this factor was taken from one bacteria and put into another, it caused changes in the second bacteria. |
| 1934 | Griffith's colleague, Oswald Avery, conducted a 10-year study to identify the transforming factor. His experiments showed that neither proteins nor RNA carry genetic information. He then wondered if DNA was the transforming agent. To answer this question, he conducted an experiment. In it, he destroyed the DNA in the first bacteria. When the DNA was destroyed, no hereditary information was transmitted to the second bacteria. Avery then concluded that DNA causes changes in the second bacteria by transmitting traits from the first bacteria. |
| 1953 | James Watson, an American geneticist, and Francis Crick, a British biophysicist, discovered the structure of DNA. To do this, they used X-ray photographs of DNA taken by New Zealand biophysicist Maurice Wilkins. Until this time, it was not known how DNA made a copy of itself in order to transmit genetic information to other cells. In 1962, the three men won the Nobel Prize for their discovery. |
| 1960's | Marshall Nirenberg, an American biochemist, and Har Gobind Khorana, an American biochemist born in India, decoded DNA and discovered the building blocks of DNA. This code consists of four chemical units, represented by the letters A (adenine), T (thymine), C (cytosine), and G (guanine). Each string of letters produces a specific amino acid. When these amino acids are combined, they create human traits such as eye color and genetic diseases. |
| 1977 | Frederick Sanger, a British biologist, developed a method to decode all of the DNA strings in one bacteria. This was the first living organism to be totally decoded. |
| 1990 | Agencies of the U.S. government funded a 15-year project to sequence the human genome. This is a map of the cell's inner workings and of all the chemicals produced by DNA that determine human characteristics and behavior. |
| 1999 | The Human Genome Project finishes sequencing the first human chromosome. |
| June 2000 | Both the U.S. government-sponsored Human Genome Project and a privately funded research group announced that they have a draft of the first human genome. |
Just like many scientific discoveries in the past, this decoding of human DNA will undoubtedly have an impact on our future in ways that are almost unimaginable today. Understanding DNA promises to give us a better understanding of human biology, new diagnostic tests for certain hereditary diseases such as cerebral palsy and breast cancer, and possibly treatments or cures for diseases such as Alzheimer's, diabetes, and heart disease. It will also help companies create drugs that match a person's genetic profile. However, there are many things that still will not be known once the 3.4 billion or so chemical units in human DNA are coded. We won't fully know how many human genes there are in the human organism, and we won't fully know how genes interact with one another.
While there is much work to be done mapping the
human genome, scientific findings in the past decade have ensured that
a more complete knowledge of human DNA and the contributions it will
make to our lives will not occur in the distant future but in our own
lifetimes.
Glossary
Alzheimer's: A mental disorder that gradually destroys vital nerve cells in the brain. Symptoms include loss of memory, judgment, and reasoning, as well as changes in mood and behavior. It is not a normal part of aging.Amino Acid: Any of 20 basic elements that make proteins.
Bacteria: A tiny one-cell organism that reproduces by cell division.
Biologist: A person who studies plants, animals, and humans. Many biologists now do research on genetics.
Cell (human): In biology, a structure surrounded by a membrane and containing genetic material (DNA) on the inside. Considered by most biologists to be the basic unit of life.
Chromosome: In organisms without a nucleus (such as bacteria), this is a circular DNA molecule used in genetic engineering. In organisms with a nucleus (including plants and humans), this is one of the threadlike structures within the nucleus that contains DNA.
Diabetes: A disorder caused by the body's decreased production or use of insulin (a hormone produced by the pancreas cells need to be able to use blood sugar).
Diagnostic test: Tests used to identify a particular disease or characteristic.
DNA: (deoxyribonucleic acid) A molecule in the form of a double helix , found within a structure known as a chromosome, within the nucleus of every living cell. First discovered in the 19th century, it controls the daily operation of a cell, and provides the genetic "blueprint" for the physical characteristics of all living organisms.
Gene: A small stretch of DNA that directs the production of proteins. A hereditary unit that occupies a specific position (locus) on the chromosome. This unit has a specific effect on the physical characteristics of the organism.
Gene mapping: Finding the relative positions of genes on a DNA molecule (chromosome) and of the distance between them.
Genetics: The study of heredity.
Hereditary disease: A physical disorder that is inherited from parents or grandparents rather than caused by environmental factors.
Heredity: The passing of certain traits from parents to their offspring through the genes.
Human genome: The complete set of genes in a cell that creates a living organism.
Human genome project: The scientific project to "read" the DNA of human chromosomes. Consists of not one project, but rather hundreds of separate research projects conducted throughout the world. The objective is to create a directory of the genes that can be used to answer questions such as what specific genes do and how they work.
Inherited trait: Ways of looking or being that are caused by the genetic make-up or environment of a living organism.
Learned traits: Ways of looking or being that are caused by the environment of a living organism.
Molecule: A chemical entity consisting of two or more atoms of the same or different elements chemically bonded together.
Nucleus (of a cell): The control center of the cell that contains chromosomes and controls the cell's actions.
Organism: Any living thing, either vegetable or animal.
Protein: The "building blocks" of our bodies that contain substances such as hormones and antibodies to regulate body functions.
RNA: (ribonucleic acid) Like DNA, this is another molecule that is important in genetics. It is different from DNA because it is single stranded (not double stranded).
Trait: Ways of looking or being. Traits that are genetic are passed down through the genes from parents to their children
Transforming factor: Something that causes a change.
White blood cells: Cells that circulate in the blood and work as part of the immune system to fight off "foreign bodies" that cause disease.
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