The Science of Maryland Agriculture

Transcription

1 Edition 3 (2016) GOAL STATEMENT: Students will learn that DNA is the molecule responsible for the inheritance of traits and will understand that selective breeding and genetic engineering are used to develop desired traits. OBJECTIVES: Students will learn that DNA is the molecule responsible for the inheritance of traits in all organisms and understand that DNA is found in all of the food that we eat. Students will learn how to extract DNA from corn and observe what large quantities of DNA look like to the naked eye. Students will understand how selective breeding and genetic engineering contribute to an increased food supply for people. Students will learn about genetically modified organisms (GMOs) in agriculture. REQUIRED MATERIALS: Goggles (1 per student) Zip-style plastic snack-sized bags (1 per group) Cone-shaped #2 coffee filters (1 per group) 5-ounce plastic cups (1 per group) Plastic pipettes (1 per group) 15 kernels of fresh sweet corn or 10 kernels of thawed frozen sweet corn (per group) If you want to experiment with other fruits or vegetables, you can substitute the corn with 1 mediumsized strawberry, 12 sweet peas, or ¼ of a medium-sized tomato. Use fresh or frozen foods, not canned. 10 ml DNA extraction buffer (per group) The teacher will need to prepare this solution in advance; see the Exploration section for details and preparation instructions. Required ingredients: a clear hair shampoo with EDTA, table salt, and nonchlorinated water. 15 ml ethanol or propanol (isopropyl) alcohol, chilled (per group) 20 ml glass test tubes (1 per group) Test tube holder or large plastic cup to hold test tube (1 per group) Paper clips (1 per group) Copies of the Corn DNA Extraction Data Sheet (1 per student) AMOUNT OF TIME TO ALLOW: minutes. Extension activities will take additional time.

2 DNA and Genes Each person is made up of trillions of microscopic cells. A person s hand has more than 2.5 billion cells! Each type of cell in the body has its own specific functions, but every cell also has genetic information in its nucleus (center) that codes for the production of the entire organism. Cells receive instructions on how to perform their functions from a molecule called DNA, or deoxyribonucleic acid. DNA is made of many subunits, called genes, which contain instructions for the production of different types of proteins. Proteins are molecules that build the structure of an organism and control a variety of functions. An organism s DNA also controls the expression of physical and behavioral traits of that organism. The shape of DNA is similar to that of a twisted ladder and is called a double helix. DNA in cells is organized into coiled structures called chromosomes. Different species have different numbers of chromosomes in their cells. DNA is tiny since it is inside microscopic cells. However, when students extract the DNA from thousands of cells together (as they will do in this lesson), it becomes visible to the naked eye. DNA controls the inheritance of traits in humans and all other living organisms. The genetic information contained in DNA is passed from parents to offspring. In people, 50% of each cell s DNA comes from the mother, and 50% comes from the father. Every person receives a different combination of genes from his or her parents. Siblings often appear similar because they share some of the same genes. Only identical twins have the exact same DNA. Selective Breeding and Genetically Modified Organisms To produce plants and animals with the most desirable traits, farmers use selective breeding by choosing plants and animals with desired traits to produce offspring that contain more of those traits. It often takes many generations to produce the desired result. Over the past several hundred years, people have developed many different varieties of plants (for example, apples are available in many varieties) and breeds of animals using selective breeding. In recent years, scientists have begun using gene mapping to find out which parts of an organism s DNA code relate to particular traits. DNA has now been mapped for many agricultural plant and animal species. Once a species DNA has been mapped, scientists can use a process called genetic engineering to produce offspring with desired traits much faster than through selective breeding. In genetic engineering, scientists add or remove DNA to change the traits an organism expresses. Most frequently, genes from one organism are removed and transferred into another organism, enabling that organism to express traits it didn t possess before. Any organism whose DNA has been altered by scientists either through addition or deletion of genes is called a genetically modified organism (GMO). Applications of Genetic Biotechnology There are more than 7 billion people on our planet, and that population is growing every day. However, the amount of land we have to produce food to feed our population is limited. By 2050, it s estimated that farmers will need to produce twice as much food as they do today to meet the world s demand. Biotechnologies like selective breeding and genetic modification can make crops more resistant to pressures like insects, diseases, and unfavorable weather and thus allow farmers to produce more food on the same amount of land.

3 The development of GMOs has caused controversy because these organisms contain gene combinations that were created by people and don t occur naturally. It is important to note that all GMOs approved for human consumption are field tested and regulated in the United States by various U.S. government agencies. There are currently eight genetically-modified crop organisms that are approved to be grown in the U.S.: corn, soybeans, cotton, canola, alfalfa, sugar beets, papaya, and squash. These crops have been modified to include genes that make them more resistant to disease, insects, and pesticides. In 1960, one American farmer fed about 29 people. Today, one American farmer feeds 155 people. Ask students to predict how or why this change occurred. Lead the conversation into a discussion about how better technology, including better plant and animal genetics, has increased the American farmers productivity. Here are some specific examples you may cite: Dairy cow genetics have improved, largely due to selective breeding, higher quality feed, and better environmental conditions such as more comfortable housing. In 1960, the average dairy cow produced 8,000 pounds of milk per year. Today the average dairy cow produces 22,000 pounds of milk per year. In 1960, the average American farmer produced 75 bushels of corn per acre. Today the average is over 160 bushels per acre. The increase in yield is attributed to improved tillage methods, better control of weeds using pesticide technology, and improved plant genetics. Before moving into the exploration section, ensure that students understand the basic form and function of DNA. Depending on the previous knowledge of the class, you may need to include a conversation on some of the principles listed in the Background Information DNA and Genes section above. Teacher s Note: Be sure to chill the ethanol or isopropyl alcohol prior to the lesson. The DNA extraction buffer should also be mixed before beginning the lesson. In a pint jar or 500 ml beaker, combine the following ingredients: 50 ml of a clear hair shampoo with EDTA (ethylenediaminetetraacetic acid), like Suave. Do not use one that contains a conditioner. 1 tsp of NaCl (table salt) 450 ml water (non-chlorinated)

4 We ve all heard that, on a microscopic level, DNA s double helix looks like a twisted ladder. But what if you could see it with the naked eye? Tell students that in this exercise they will be breaking apart corn cells, releasing the DNA from the nucleus, and separating the DNA from the rest of the cell s structures. All of those DNA strands together will be visible without a microscope! Show students a graphic of where DNA is found in a cell. Help them interpret the graphic and what it shows about DNA. (Observant students may notice that, because it lacks a cell wall, the cell in the graphic is an animal cell. However, the location and structure of DNA is the same in both plant and animals cells.) Divide students into small groups and distribute the Corn DNA Extraction Data Sheet worksheet. Following are the instructions students should follow to complete the experiment. Predict the Appearance of DNA 1. Answer question #1 on your data sheet by predicting what DNA will look like after it is extracted from corn cells. Prepare the DNA 2. Have one member of your group get 15 kernels of fresh sweet corn or 10 kernels of thawed frozen sweet corn for the group to use. (Teacher s note: If you want to experiment with other fruits or vegetables, you can substitute the corn with 1 large strawberry, 12 sweet peas, or ¼ of a medium-sized tomato. You may want to assign a different fruit or

5 vegetable to each group and have groups compare their results.) 3. Place the corn kernels in a zip-style plastic snack-sized bag, close the bag, and mash the kernels for 1-2 minutes. 4. Using a pipette, add 10 ml of the extraction buffer to the bag and close the bag. 5. Mix the solution for 1 minute. 6. Put the cone-shaped #2 coffee filter over the top of the 5 oz. plastic cup so that it hangs inside but does not touch the bottom of the cup. 7. Pour the solution into the filter and let it drain into the cup for 10 minutes. 8. While you wait for the solution to drain, complete questions #2-4 on your data sheet. Transfer the DNA Extract 9. Measure 15 ml of chilled ethanol or isopropyl alcohol into a glass test tube or similar container. 10. Using the pipette, transfer the extract from the bottom of the cup into the alcohol in the test tube. (You will need to add at least.5 ml and up to 3 ml of the extract.) Once the extract is added, gently and slowly swirl the tube for 2-5 seconds. (Do not shake the tube.) 11. Complete question #5 on your data sheet. Observe the DNA 12. Look very closely at the solution and observe for 5-10 minutes. 13. Complete question #6 on your data sheet. Remove the DNA 14. Using a large paper clip, remove the DNA from the test tube and observe. You may need to bend the paperclip into a hook shape before you attempt to remove the DNA. Have students discuss what they observed within their group or as a class. Lead the conversation into a discussion of the principles of selective breeding, gene mapping, and genetic engineering. You may want to refer to the Background Information section above for details and points to include in your discussion. Have students work individually or in groups to research genetically modified organisms. You may have them complete the Genetically Modified Organism Research Guide and prepare a presentation for their classmates. Assign a different genetically modified crop to each group.

6 Biotechnologist This scientist develops plants and animals that have better traits and higher yields. They work at the cellular level using a variety of methods to change the genetic information in the DNA. Plant or Animal Geneticist This scientist studies DNA and how traits affect characteristics like growth, production, and reproduction in plants or animals. Plant or Animal Pathologist This scientist deals with the causes, damages caused by, and control of diseases in plants or animals. Seed Production Scientist This scientist works to produce seeds that have positive traits and can grow and reproduce successfully. Student understanding can be evaluated through class discussion or assessment of completed activity data sheets. The following questions may also be used to evaluate student learning. 1. Briefly describe the steps you took to extract the DNA from your sample. 2. DNA is too small to be seen with the naked eye. How were you able to see the extracted DNA without a microscope? 3. How does being able to isolate an organism s DNA help scientists improve agriculture? Module 3: Strawberry DNA Extraction, Pioneer Hi-Bred International. <ucbiotech.org/resources/display/ files/dna_extraction_from_strawberrie.pdf> Innovation in Agriculture: The Pluses of Biotechnology in Corn Production, National Corn Growers Association. < How to Explain DNA to Kids. <tfscientist.hubpages.com/hub/explaining-dna-to-a-six-year-old> October is Get to Know GMOs Month, GMO Answers. <gmoanswers.com/studies/october-get-knowgmos-month> National Agricultural Statistics Service. <

7 Corn DNA Extraction Instructions Work in your lab group to complete the experiment. Goggles should be worn during this experiment. Predict the Appearance of DNA 1. Answer question #1 on your data sheet by predicting what DNA will look like after it is extracted from corn cells. Prepare the DNA 2. Have one member of your group get 15 kernels of fresh sweet corn or 10 kernels of thawed frozen sweet corn for the group to use. (Teacher s note: If you want to experiment with other fruits or vegetables, you can substitute the corn with 1 large strawberry, 12 sweet peas, or ¼ of a medium-sized tomato. You may want to assign a different fruit or vegetable to each group and have groups compare their results.) 3. Place the corn kernels in a zip-style plastic snack-sized bag, close the bag, and mash the kernels for 1-2 minutes. 4. Using a pipette, add 10 ml of the extraction buffer to the bag and close the bag. 5. Mix the solution for 1 minute. 6. Put the cone-shaped #2 coffee filter over the top of the 5 oz. plastic cup so that it hangs inside but does not touch the bottom of the cup. 7. Pour the solution into the filter and let it drain into the cup for 10 minutes. 8. While you wait for the solution to drain, complete questions #2-4 on your data sheet. Transfer the DNA Extract 9. Measure 15 ml of chilled ethanol or isopropyl alcohol into a glass test tube or similar container. 10. Using the pipette, transfer the extract from the bottom of the cup into the alcohol in the test tube. (You will need to add at least.5 ml and up to 3 ml of the extract.) Once the extract is added, gently and slowly swirl the tube for 2-5 seconds. (Do not shake the tube.) 11. Complete question #5 on your data sheet. Observe the DNA 12. Look very closely at the solution and observe for 5-10 minutes. 13. Complete question #6 on your data sheet. Remove the DNA 14. Using a large paper clip, remove the DNA from the test tube and observe. You may need to bend the paperclip into a hook shape before you attempt to remove the DNA. 15. Complete question #7 on your data sheet. because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry,

8 Name: Date: Period: Corn DNA Extraction Data Sheet Predict the Appearance of DNA 1. Draw and describe what you think the corn DNA will look like when you extract it from the plant cells. Prepare the DNA 2. Why was it necessary to mash the corn kernels? 3. What is the purpose of the extraction solution which contains soap, salt, and water? 4. What is the purpose of the filter? Transfer the DNA extract 5. Describe what happens to the DNA solution as it is added to the ethanol/isopropanol alcohol. because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry,

9 Name: Date: Period: Corn DNA Extraction Data Sheet Predict the Appearance of DNA 6. After observing the mixture for 5-10 minutes, draw and describe what you see. Remove the DNA 7. Draw and describe what you see after the DNA has been removed from the test tube. because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry,

10 Name: Date: Period: TEACHER KEY: Corn DNA Extraction Data Sheet Predict the Appearance of DNA 1. Draw and describe what you think the corn DNA will look like when you extract it from the plant cells. Sample answers: different colors, twisted ladder, double helix. (Answers may vary depending on what students already know about DNA.) Prepare the DNA 2. Why was it necessary to mash the corn kernels? To break open the cells. 3. What is the purpose of the extraction solution which contains soap, salt, and water? The soap and the salt in the extraction solution help release DNA from the cells. 4. What is the purpose of the filter? The filter helps separate the DNA from the large parts of the corn kernel. Transfer the DNA extract 5. Describe what happens to the DNA solution as it is added to the ethanol/isopropanol alcohol. The DNA began to settle and cling together at the bottom of the test tube. Observe the DNA 6. After observing the mixture for 5-10 minutes, draw and describe what you see. The DNA strands cling to other DNA strands and form a layer in the tube. Remove the DNA 7. Draw and describe what you see after the DNA has been removed from the test tube. The DNA looks like fuzzy, white threads, twisted and clumped together. because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry,

11 Name: Date: Period: Name of the genetically modified organism: Why was it developed? Genetically Modified Organisms Research Guide When was it developed? What makes it different from a non-gmo organism? What are the benefits? What are the potential problems/concerns? List your references: because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry,