Ask students to brainstorm traits they have that are passed on from their parents, such as eye color, hair texture, and facial characteristics. Then ask them how these traits are passed on from one generation to the next. The answer is DNA, or deoxyribonucleic acid. Explain that all organisms carry an elaborate blueprint containing the information necessary to develop and maintain life. This “manual of instructions” is located in a chemical molecule called DNA. DNA is found within a person’s genes. Genes are small structures found in chromosomes, structures within the nucleus of cells.
2.
Tell students that DNA works something like the alphabet. While the alphabet has 26 letters, DNA’s “alphabet” has only four letters. These letters are guanine (G), adenine (A), cytosine (C), and thymine (T). Just as the 26 letters of the alphabet can be used to form millions of words for communication, DNA’s alphabet can be combined to form codes with more than five billion combinations of G’s, A’s, T’s, and C’s. The differences in these combinations result in differences among human beings.
3.
The DNA molecule consists of two strands that form a double helix, a spiraling shape much like a twisted ladder. The DNA molecule has a sugar component, a phosphate component, and four different bases—adenine, thymine, cytosine, and guanine. To help students understand how these components fit together to form DNA, have each student make a model of DNA with fishing line, dried pasta, and different-colored pipe cleaners.
4.
First, give each student 2 pieces of line, 18 pieces of pinwheel pasta, 16 pieces of ziti pasta, and different-colored chenille stems (pipe cleaners). Explain that the pinwheel pasta represents the sugar component, the ziti pasta the phosphate, and the chenille stems each of the bases.
5.
Tell students to start with the pinwheel pasta and alternate with the ziti pasta as they thread the pasta on the line. On each line, they should string nine pieces of pinwheel pasta alternating with eight pieces of ziti. Wrap the line around the final piece of pasta at the end of each line so that the pasta does not fall off. After pasta has been strung on both lines, each line should have a total of 17 alternating pieces of pasta. Have students lay the two lines side by side.
6.
Then give students the “code” for the chenille stems—the blue stem represents adenine; the green stem, thymine; the purple stem, cytosine; and the orange stem, guanine. Explain that the bases in DNA are found in pairs and that adenine always pairs with thymine and cytosine always pairs with guanine.
7.
Have students represent these base pairs with twisted chenille stems. First, have them twist the eight blue stems and eight green stems together, making a total of eight blue-green stems, about 2 inches long. Likewise, have them twist the eight purple and eight orange stems together, making a total of eight purple-orange stems, about 2 inches long. Students will find that the chenille stems twist together easily.
8.
Now, have students create a “ladder” using the pasta lines as the sides and the twisted chenille stems as steps. Beginning at the top, students should connect the two ends of a twisted chenille stem to the top pasta pieces on the two lines. Then use a second chenille stem to connect the next two pasta pieces directly across from each other. They should continue building their ladder, one step at a time, until they have connected the bottom two pieces of pasta. Remind them that they can place the twisted chenille stems in any order. (The blue-green stems do not have to alternate with the orange-purple stems.) After all the stems have been woven, the DNA model is complete.
9.
Using the DNA models, discuss the following questions with the class. To enhance the discussion, you may want students to look up additional information in other resources.
How do the bases pair up in a DNA molecule? How does your model help you figure this out?
What differentiates one DNA molecule from another? How could you change your DNA model to reflect changes among DNA molecules?
How do you think a DNA molecule makes an exact copy of itself? How does its structure help it do so?
10.
Assign the Take-Home Activity Sheet: Crack the DNA Vocabulary Code for homework. Then go over the vocabulary words to make sure that students have mastered them.
Have older students use this topic to integrate art and science. Instruct them to design and create a DNA model using materials of their own choice. Suggested materials include stained glass, clay, beads, buttons, wood pieces, recycled materials, and food items. They should include a key that explains what each item represents. After students have completed their models, have them display the models in the classroom.
What is the relationship between chromosomes and genes and between genes and DNA molecules?
2.
For the past several years, scientists have been working to map and sequence the human genome—that is, all the instructions needed for making an organism. Aptly called the Human Genome Project, it is considered one of the biggest milestones in scientific history. Why do you think this project is so important? What types of information could it provide?
3.
Do you think we have a better chance of curing genetic diseases, such as muscular dystrophy or cystic fibrosis, with our increased knowledge of genetic codes? What issues does this increased knowledge raise?
4.
Scientists have been working to understand genes since the 19th century. Research the work of the Austrian monk and biologist Gregor Mendel. Why is he considered the “father of genetics”? What organisms did he study to learn how traits are passed on from parents to offspring?
5.
In 1997, scientists were able to clone a sheep. What do you think the potential of cloning is? Do you think that scientists will be able to clone people some day? What dangers does that possibility raise?
6.
If scientists can retrieve DNA from the remains of extinct animals, they might be able to clone them. What are some potential dangers of cloning extinct mammals, such as the mammoth? What are some advantages of cloning extinct mammals?
Use the following three-point rubric to evaluate students’ work during this lesson. Students should be able to follow directions to make their DNA models, identify the parts of the model, and participate in the class discussion about DNA.
Three points: students followed directions accurately, completed their model completely and accurately, identified each part of the model, and actively participated in the class discussion about DNA.
Two points: students followed most of the directions accurately, completed their model but had a couple of errors, identified most parts of the model, and participated somewhat in the class discussion.
One point: students followed some of the directions accurately but were not able to complete their model, identified some parts of the model, and participated a little bit in the class discussion.
The Pros and Cons of Genetic Research
The Human Genome Project has generated much excitement recently. People have reacted both positively and negatively to scientists’ current findings. Have groups of three or four students conduct research on the most current information available from this project. Then have them share their findings with the class. What ethical dilemmas do your students feel should be addressed before further research is conducted? How will the Human Genome Project revolutionize the way medicine is practiced?
Mammoths
Adrian Lister and Paul Bahn. Macmillan, 1994.
Frozen carcasses and skeletons of mammoths have been discovered throughout the Northern Hemisphere, from Siberia to South Dakota. This book explains what scientists have learned about the origins of mammoths, their lives, and how they became extinct. The interactions of mammoths and prehistoric humans are also discussed. Dramatic and informative illustrations and photographs enrich the book. Includes a map and guide to mammoth sites and museums around the world.
The Science of Jurassic Park and the Lost World or, How to Build a Dinosaur
Rob DeSalle and David Lindley. BasicBooks/HarperCollins, 1997.
Could an extinct creature really be cloned and brought to life as we've seen in the movies? The two scientists who authored this book provide a light-hearted, but scientifically accurate discussion of how the movies got it wrong and what it really would take to accomplish such a feat.
What Drove the Giants of the Ice Age to Extinction?
An extensive informational site, including excavation sites and techniques, historical perspectives, skeletal diagrams, classroom lesson plans and tests, web links, and books.
Mammoth Site Museum of Hot Springs, South Dakota
Includes a museum tour, mammoth information and paleontology links, educational activities, and a Quicktime video of an actual scientific excavation.
All About Mammoths
Specific and easy-to-read information about mammoths.
Definition: The genetic material contained in every cell and unique to each individual. Context: DNA is responsible for the enormous possibilities for variability in the living world.
Definition: A complex protein that can catalyze biochemical reactions in the body. Context: In addition to determining heredity, genes also carry the information needed for constructing enzymes needed for essential biochemical reactions.
Definition: The study of what genes are made of, how they work, and how they are inherited. Context: The field of genetics includes understanding how living systems grow and are maintained during their life span and how they duplicate and pass on genetic material.
Definition: The basic structural unit of DNA. Context: Each strand of a DNA molecule is a linear arrangement of nucleotides, which are each composed of one sugar, one phosphate, and one nitrogenous base.
Definition: A body found in most plant and animal cells that contains the genetic material. Context: Scientists were able to break the genetic code within the nucleus of cells.
Definition: A large, complex molecule made up of amino acids. Context: Context: Human beings can synthesize at least 100,000 different kinds of proteins.
Definition: The material from which ribonucleic acid (RNA) is made. Context: Ribosome is key to protein synthesis, an essential part of the genetic code.
Definition: A transient intermediary molecule similar to a single strand of DNA. Context: The protein-coding instructions from genes are transmitted indirectly through a messenger RNA molecule, which serves as a template for protein synthesis.
This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of the Mid-continent Research for Education and Learning in Aurora, Colorado.
Grade level: 6-8 Subject area: Life Science Standard:
Understands the genetic basis for the transfer of biological characteristics from one generation to the next. Benchmarks:
Knows that the characteristics of an organism can be described in terms of a combination of traits; some traits are inherited and others result from interactions with the environment.
Grade level: 6-8 Subject area: Life Science Standard:
Knows that hereditary information is contained in genes (located in the chromosomes of each cell), each of which carries a single unit of information; an inherited trait of an individual can be determined by either one or many genes, and a single gene can influence more than one trait. Benchmarks:
Knows that the characteristics of an organism can be described in terms of a combination of traits; some traits are inherited and others result from interactions with the environment.
