A Recipe for Genetics: Selective Breeding and Transgenics
Students will identify technologies that have changed the way humans affect the inheritance of desired traits in organisms; compare and contrast selective breeding methods to genetic engineering techniques; and analyze data to determine the best solution for cultivating selected desired traits in organisms. Grades 6-8
- Then and Now PowerPoint slides
- Natural Selection vs Artificial Selection video
- Selective Breeding station cards,1-2 sets
- Selective Breeding handout, 1 copy per student
- GMO Issues cards, 1 set per group of 4 students
- GMO Solutions cards, 1 set per group of 4 students
- GMO Results cards, 1 set per group of 4 students
Concept Elaboration and Evaluation
Essential Files (maps, charts, pictures, or documents)
agriculture: the science, art, or practice of cultivating the soil, producing crops, and raising livestock and in varying degrees the preparation and marketing of the resulting products
animal husbandry: the science of breeding and caring for farm animals
artificial selection: the intentional breeding of plants and animals to produce specific, desirable traits
domesticate: to breed a population of animals or plants to serve the purposes of human beings and to need and accept human care
gene: a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring
genetically engineered (GE): an organism or crop whose characteristics have been deliberately modified by manipulating its genetic material
genetically modified organism (GMO): any organism whose genetic material has been altered using genetic engineering techniques
selective breeding: process by which humans control the breeding of plants or animals in order to exhibit or eliminate a particular characteristic
transgenic: containing a gene that has been transferred from one organism to another and acts as a synonym for genetically modified
Did You Know? (Ag Facts)
- Even though the process of artificial selection had been in use for centuries to create livestock and crops with desirable characteristics, Charles Darwin is credited with coining the term "artificial selection" in his book that he wrote upon returning from the Galapagos Islands.15
- There is no substantiated evidence of a difference in risk to human health between current commercially available genetically modified (GM) crops and conventionally bred crops.5
- Genetically modified (GM) crops in the United States are regulated by the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), and the United States Department of Agriculture (USDA).6
Background Agricultural Connections
The development of agriculture, or the intentional production of plants and animals for human use, allowed people to settle in one place and form villages and cities. Approximately 10,000 years ago, the domestication of plants and animals for human use began to develop rapidly. As hunter-gatherers became farmers, they learned to select and save seeds from plants that produced the best crops and to breed the animals that were best suited to meet people’s needs. The first steps of domestication probably happened by accident, but soon farmers deliberately practiced selective breeding to develop crops and livestock more suited to their needs.11 Selective breeding was likely the earliest form of biotechnology used by humans to improve the genetic characteristics of plants and animals. Biotechnology includes any use of science or technology to alter the genetic characteristics of a particular plant or animal. There are many examples of biotechnology. This lesson illustrates two— selective breeding and transgenesis.
Selective breeding (also known as artificial selection) is a technique still extensively used by crop and livestock producers today. Selective breeding allows producers to select and breed parent organisms with desired traits to produce offspring with more desirable characteristics. This process creates offspring who are genetically superior to the parent organisms, thus improving plants and animals with each generation. The successful results of selective breeding throughout the years can be seen in crop and livestock production today.
Many crops, including wheat, have been genetically improved through selective breeding. Dr. Norman Borlaug was a research scientist assigned to improve the wheat plant in Mexico. By studying genetics and utilizing selective breeding, he was able to develop short-strawed, disease-resistant wheat that was high yielding. Dr. Borlaug is known as the “Father of the Green Revolution” for his improvement of wheat and was awarded the Nobel Peace Prize for a lifetime of work to feed a hungry world.4
In the livestock industry, today’s cattle are also evidence of successful selective breeding. Dairy and beef cattle are both highly efficient animals that produce more milk and meat than in years past. Today, there are only 9 million dairy cows in the United States compared to 25 million cows in 1950; however, today’s dairy cows are producing 60% more milk.12 In 1944, the average dairy cow produced 548 gallons of milk in one year. The average dairy cow today is able to produce 2,429 gallons of milk in one year.13 Beef production has seen similar success. Compared to 1977, today’s beef ranchers are producing the same amount of beef with 33% fewer cattle.10 It is important to note that proper nutrition, better health care, and good animal husbandry also play a key role in improving genetics.
Genetically modified organisms (GMOs) can also be referred to as genetically engineered (GE) or transgenic. These terms all describe an organism that has a copy of a gene not previously found in that species.
A genetically modified crop is a crop that has had its genetic makeup altered in order to produce a more desirable outcome, such as resistance to disease, drought tolerance, or change in size.1 This type of plant breeding differs from selective breeding because scientists take the desirable gene from one organism’s DNA and transfer it to another organism’s DNA, creating a new, stronger product—one that is impossible to produce through traditional breeding.1
Currently, there are ten genetically modified crops that have been approved and are available on the U.S. market: corn, soybeans, cotton, canola, sugar beets, alfalfa, papaya, squash, apples, and potatoes. To learn more about the safety and regulatory process of GM crops refer to the Background Agricultural Connections section of the lesson plan, Evaluating GMO Perspectives.
Interest Approach - Engagement
- Begin by asking students to think about the food they eat.
- Has our food always looked the same?
- How has food changed over the years?
- Why has food changed?
- Project the Then and Now PowerPoint on the board.
- Show slides 2-9 to the students. Allow students to look at the ancient/wild varieties of food and guess what it is. (e.g. wild banana, wild watermelon, ancient carrot and corn).
- When students compare the older foods to today’s foods, ask them to point out visible differences including size, shape, color, and the amount of edible flesh. Ask them how they think the taste would compare.
- Project slide 10 on the board and ask students, “What has caused these traits to change?” Lead students to use their existing knowledge to explain what they can about how humans have influenced the look and taste of bananas, carrots, corn, and watermelon? (Through selective breeding.)
- Project slide 11 on the board. Ask students to think about animal traits. Have humans influenced animal traits and genetics? (Yes, by selecting plants and animals with desired traits and breeding those animals to produce offspring with the desired traits.)
- Explain to students that they will discover two methods used by agriculturists and scientists to improve the genetics and traits of the food we eat.
Activity 1: A Recipe for DNA
- Divide the class into six groups.
- Pass out a recipe card to each group.
- Note: The class can also be divided into smaller groups and two copies of each recipe can be distributed if smaller groups would be more ideal for your class.
- Instruct students to read through the ingredients and baking instructions on their recipe card. Ask, "If you were to follow the instructions on your recipe, what product will you end up with?" (Each recipe is for a type of cookie.)
- Allow each group to share their recipe guesses with the class.
- Show students the type of cookie each of their recipes make using the Cookie Key image.
- Ask students:
- Why would each of you end up with a different cookie?” (While each recipe has some similar ingredients, it also includes different ingredients and instructions for mixing and baking resulting in a different type of cookie.)
- Are there any improvements that could be made to your recipes? (Yes, depending on what kind of cookie you want.)
- Could you alter your recipes? (Yes, ingredients could be substituted with other baking alternatives, ingredients could be taken out due to food allergies or intolerance, or ingredients could be added to obtain a desired outcome of some sort.)
- Now ask the students to think about their cookie recipes and relate it to what they know about DNA. Ask:
- What is DNA?
- How can the DNA in living organisms relate to a cookie recipe? (DNA contains “ingredients” and a set of instructions for living organisms. DNA determines the genetic material and outcome of each living organism.)
- Can we improve or alter the DNA of plants and animals? (Yes, through selective breeding and genetic engineering.)
- Show students the image, A Recipe for DNA and explain that our DNA is made of different “ingredients” including a sugar phosphate backbone, nitrogenous bases, and hydrogen bonds. Explain to students that adenine (A) always pairs with thymine (T) and cytosine (C) always pairs with guanine (G). The order in which these nitrogenous bases line up acts as a set of instructions for DNA that determines the characteristics and traits in all living organisms.
- Explain to students that our basic knowledge of DNA and genetic inheritance has allowed humans to influence the genetic traits of plants and animals.
Activity 2: Selective Breeding
- Show the video, Natural Selection vs Artificial Selection.
- Following the video, make a Venn Diagram with students to identify the similarities and differences between natural selection and artificial selection (also known as selective breeding). If helpful, display the Natural Selection vs Artificial Selection Venn Diagram.
- Tip: Be sure students recognize that the terms artificial selection and selective breeding are synonymous.
- Set up four different stations around the classroom using the Selective Breeding Station Cards.
- Divide the class into four groups and assign each group a specific station around the classroom.
- Note: A second set of station cards can be printed so students are in smaller groups.
- Pass out one Selective Breeding handout to each student.
- Explain to students that they will be rotating through 4 stations. They will have approximately 5 minutes at each station to read the station card instructions, background information, and scenario.
- Set a timer. Consider projecting the timer in the classroom to allow students to gauge their time at each station. Adjust the time limit as necessary. After time is up, groups should rotate to the next station until all four stations have been visited.
- Bring the class back together to discuss each of the stations.
- Allow students to share their thoughts and answers for each of the stations.
- Which animals did they select for breeding purposes?
- How does selective breeding (artificial selection) benefit livestock producers?
- How do these selective breeding scenarios affect us?
- Discuss each of the following scenarios with students.
- Milk Production
- Which cows did you select and why? (Ideally, students should have selected the cows 6, 5, 2, and 3)
- How does selective breeding in the dairy industry affect us as consumers? (Dairy producers are not only selecting healthy livestock but breeding and improving traits that directly affect our food supply. The milk produced on dairies is used to make many products including cheese, yogurt, butter, sour cream, and ice cream.)
- Butterfat Content
- Which Jersey cows did students select to maintain a high butterfat content in the herd? (Ideally, students should have selected the cows 1, 4, 3, and 2)
- Birthweight and Weaning Weight
- Which Angus bull has a low birthweight for small cows, but high weaning weight? Will some students sacrifice a low birthweight to have a very high weaning weight? Remind students that when beef producers sell the calves in the fall, they are paid by the pound, so high weaning weights mean more money. However, calves born at 90-100 pounds can cause problems at birth for heifers and small cows. Ideally, bull 1 with an 80-pound birthweight will still give producers a large calf at weaning.)
- Horned and Polled Cattle
- Which cows should be selected to ensure no offspring have horns? (Cows 3, 4 and 5. When using a horned bull with a genotype (pp), cows with the genotype (PP) should be selected for breeding. (pp) x (PP) = (Pp) The bull will always pass on a recessive horned gene (p) to his offspring, so if you cross a horned bull (pp) with a heterozygous cow (Pp), there is a chance for horned offspring. Breeding the horned bull (pp) with the horned cow (pp) will give producers a 100% chance of having horned offspring.
- Milk Production
- Now ask students what other technologies or management practices can affect desired traits in livestock. Explain that proper care and animal husbandry can help maintain desired traits and genetics. Close monitoring of animal health, proper nutrition, shelter, and waste management all affect livestock production. A calf may be born with superior genetics, but if it is not taken care of properly or fed correctly, inherited traits may be negatively affected.
- To transition into Activity 3, ask students, “What does it mean if an organism is genetically modified?” Allow students to answer or brainstorm ideas.
Activity 3: GMO Issues, Solutions, and Results
- Divide the class into groups of four students.
- Start by passing out a set of GMO Issues cards to each group.
- Instruct groups to read through each of the cards. Explain that each card describes a challenge.
- Discuss each of the issues as a class. Consider asking students the following questions to lead a class discussion:
- Are you familiar with any of these issues related to the production of our food and fiber?
- What are the negative impacts of these issues? (food waste, malnutrition, inefficient use of natural resources like water and soil nutrients, reduced production of food and fiber that humans need.)
- Who is affected by these issues? (Farmers and consumers, so everyone.)
- Can any of the issues be resolved? (Yes.)
- Ask students to brainstorm possible solutions. Prompt students to think about what they have learned about selective breeding. What limitations would selective breeding present?
- Next, pass out a set of GMO Solutions cards to each group of students.
- Instruct students to read through the solutions and match each of the solutions to an issue.
- Pass out a set of GMO Results cards to each group of students. (This will be their third and final set of cards.)
- Instruct students to match each of the results to the issues and solutions cards. Each match should include one GMO issue, solution, and result.
- Discuss each of the GMO cards. Explain that there are currently 10 genetically modified crops available on the U.S. market.
|An important point of science and agricultural literacy is for students to recognize which crops in the United States have a genetically modified variety available for farmers to grow. Grocery stores contain many, many foods with a "non-GMO" label that do not actually have a GMO variety. This leads to the misconception that many or most foods on the market are GMOs.|
- For a brief explanation of the process of creating a GMO, watch How Are GMOs Made? The Genetically Modified Hawaiian Papaya Case Study.
- Summarize by explaining that genetically modified organisms (GMOs) are created using a scientific process called transgenesis which refers to the process of transferring a gene from one organism to another with the intent of acquiring a new genetic trait.
Concept Elaboration and Evaluation
- After conducting these activities students should be able to identify similarities and differences between selective breeding and transgenesis. Draw a Venn Diagram on the board labeling one circle "Selective Breeding" and the other circle "Transgenesis."
- Pass out the Venn Diagram Prompts to various students in the class and have them add the strip of paper to the correct portion of the diagram. Discuss and provide clarification as needed.
- Review and summarize the following key concepts with your students:
- DNA makes up the instructions for all living things.
- Humans can influence the inheritance of traits by selecting only parents that have desired traits through a process called selective breeding (also known as artificial selection).
- Technology can increase our ability to select and perpetuate helpful genetic traits in the plants and animals that provide our food. Transgenics is one example.
Selective breeding and transgenics are just two breeding techniques. Use the Crop Modification Techniques infographic to introduce more.
Activity 2 designed by Chrissy Dittmer from Iowa Agriculture in the Classroom
Suggested Companion Resources
- Making a New Apple Cultivar
- Modeling Selective Breeding with Starburst®
- Selectively Breeding Sheep: Punnet Square Practice
- Crop Modification Techniques
- CRISPR: A Word Processor for Editing the Genome Video
- Genetically Modified Food: Good, Bad, Ugly
- How Mendel's Pea Plants Helped Us Understand Genetics
- Learn GMO
- Natural GMO? Sweet Potato Genetically Modified 8,000 Years Ago
- Why are GMOs Bad?
- GMO Answers
- Genetic Science Learning Center