Using the context of apples, students will apply their knowledge of heredity and genetics to distinguish between sexual and asexual reproduction as they explain how new varieties of apples are developed and then propagated to meet consumer demand for a tasty, uniform, consistent product.
Ask students to think about their favorite apple. Ask them why that variety is their favorite. Ask them why they think a green Granny Smith apple is so tart/sour? This should lead to a discussion about various apple traits such as sweetness, tartness, flavors, crunchiness, color, etc.
Tell students that there are thousands of varieties of apples grown in the United States. Most of the varieties will not be familiar to them because they are only found in orchards grown for research, the development of new apple varieties, or hobby orchards. Challenge students to try to list the top 10 apple varieties in the United States. These varieties are more likely to be familiar to your students in addition to other local varieties.
Ask students if they know how these different apple varieties became available.
Ask your students to use their understanding of heredity and genetics to explain how apple varieties could be developed. Use student responses to transition to Activity 1.
This lesson investigates the phenomenon of apple taste along with other observed apple characteristics. Natural phenomena are observable events that occur in the universe that we can use our science knowledge to explain or predict.
Students carry out investigations to compare the Braeburn, Royal Gala, and Jazz apples. Students ask and refine questions that lead to descriptions and explanations about the different traits found in apples such as color, taste, texture, and size.
The traits found in apple varieties are determined by their genetic makeup, or genotype. Heritable traits are passed from parent to offspring.
How are new varieties of apples created?
Asking Questions and Defining Problems
Students use science to ask and refine questions that lead to explanations about the process of selectively breeding apples to produce new apple varieties with desirable traits.
Apple breeders cross pollinate the flowers of specific apple varieties (sexual propagation) and then plant the seeds to obtain a tree and apples genetically different than the parent trees. It takes hundreds or even thousands of crosses, to find the desirable result.
What makes every apple of a given variety taste and look the same?
Constructing Explanations and Designing Solutions
Students can use science to explain that forms of asexual propagation produce genetically identical offspring.
In contrast to apple breeders, apple farmers use grafting to produce new apple trees. This form of asexual plant propagation allows the genetics of each variety of apple to be exact clones, therefore producing a consistent crop of apples for consumers.
Activity 1: Apple Genetics - Making them Different (Episode Questions 1 and 2)
Give each student one copy of the Apple Genetics worksheet. Divide the class into small groups of students (2-4).
Give each group of students the following supplies:
1 paper plate (this will be the cutting board as well as an area to keep the apples)
1 Braeburn Apple
1 Royal Gala Apple (Note: DO NOT hand out the Jazz apple yet).
1 knife (or pre-slice apples)
Have students draw a line down the center of their paper plate and label each side with "Gala" or "Braeburn." The apples will look similar, so it will be important to avoid confusing the two apples.
Have students complete "Part 1" and "Part 2" of the worksheet and then stop.
Project the Apple Genetics PowerPoint for students to see. Using slide 2, hold a brief class discussion about the traits they have observed in the apples so far. Draw on the student's prior knowledge of heredity and genetics to conclude that each trait is an expression of its genotype.
Use slide 3 of the PowerPoint to review vocabulary if needed. Make sure students are familiar with the terms.
Have students complete "Part 3" of the worksheet to review the possible genotypes of the Gala and Braeburn apples. These genotypes can be found on the worksheet and slide 4-5 of the PowerPoint.
Once students have finished their Punnet squares, give each group of students a Jazz apple. Students will follow the same procedure and complete "Part 4" and "Part 5" of the worksheet.
Facilitate a class discussion about the 3 varieties of apple (slide 6). Reveal to the students that the Jazz apple is a cross between the Gala and Braeburn apple. Using slide 7, share a few more facts about the Jazz Apple.
Talk about the concept of crossbreeding and how it is used to produce better quality organisms (slide 8).
Explain that the Honeycrisp apple (slide 9) was also developed by crossbreeding, and is a competitor of the Jazz apple.
Summarize with students by connecting what they know about genetics with what they have learned about apples:
Genes determine genetic traits found in apples such as color, taste, and texture.
To develop a new, improved variety of apple, apple breeders cross pollinate apple varieties. This form of sexual reproduction results in an offspring (seed) that is genetically different from the parent trees.
Scientists use a knowledge of genetics and heredity to cross breed apples and produce new varieties of apples. The Jazz and Honeycrisp apples are examples.
Stability and Change: For both designed and natural systems, conditions that affect stability and factors that control rates of change are critical elements to consider and understand.
Activity 2: Apple Genetics - Keeping Them the Same (Episode Question 3)
Ask students if they have ever eaten Jelly Belly jelly beans. Have they ever eaten or heard of the Jelly Belly jelly beans that have "bad" flavors like toothpaste, stinkbug, or stinky socks? (Perhaps in the game Beanboozled.) While this may be a fun game or practical joke, have a discussion with your students about what they (as consumers) want in their food. Conclude that every time they purchase milk, meat, bread, vegetables... or an apple, they want it to taste consistently the same without surprises.
Students have just learned how new varieties of apples are created. Ask, "How do apple farmers all across the nation grow specific varieties of apple that all taste and look the same? For example, how does a Granny Smith always taste like a Granny Smith and a Gala always taste like a Gala?" Does a [Granny Smith] grown in one region of the country taste the same as a [Granny Smith] grown in another region of the country?
From the video, students should recognize grafting as the answer to the question. Apple farmers do not grow trees from seed, they use a technique called grafting (slide 10).
Ask students, "What is the genetic similarity of two trees grafted from the same source?" (They are genetically identical clones. Therefore, every apple tree grafted from the same source will produce apples with the same genetic makeup.)
Summarize with students by connecting what they know about genetics with what they have just learned about apples:
Grafting, a form of asexual propagation is used by apple farmers to produce the apples we eat. It produces apples consistent to consumer expectations for each variety of apple by eliminating the genetic variability of sexual propagation methods.
In addition to growing a consistent apple crop, farmers use grafting to propagate apple trees because it is significantly faster than growing a tree from seed. An apple tree grown from seed will take 6-10 years to produce fruit. A grafted apple tree will take 2-3 years depending on the type and size of the graft.
Concept Elaboration and Evaluation:
After completing these activities, have students create a Venn Diagram to list both the similarities and differences found in sexual and asexual propagation methods. Discuss the benefits and drawbacks of each.
Phenomena Episode Extensions:
Effective phenomena-based instruction continues to evolve as students learn. New questions should arise throughout the learning process. The following questions may arise providing opportunity for other episodes in this storyline:
Why can other fruits and vegetables be propagated with sexual reproduction (seeds) and produce a consistent crop, but apples cannot?
What makes an apple (such as the Honeycrisp) crunchy?
How was the Opal apple selectively bred to not brown after it is cut?
How was the Arctic® apple genetically engineered to be non-browning?
We welcome your feedback! Please take a minute to tell us how to make this lesson better or to give us a few gold stars!
If cut apples are in the room at the end of the lesson, ask students if they see any browning occurring. Discuss what causes this. Teach students about Arctic apples, a genetically modified apple which does not brown. Compare and contrast to the Opal apple, an apple variety selectively bred to be non-browning.
Activity 1 was originally written in the lesson "Apple Genetics" written by Kevin Atterberg (Culler Middle School, Lincoln NE), Erin Ingram, and Molly Brandt (University of Nebraska-Lincoln, IANR Science Literacy Initiative). The lesson was updated in 2018 to follow a phenomena-based format.
Phenomenon chart adapted from work by Susan German. German, S. (2017, December). Creating conceptual storylines. Science Scope, 41(4), 26-28. German, S. (2018, January). The steps of a conceptual storyline. Science Scope, 41(5), 32-34.
Describe examples where selective breeding has resulted in new varieties of cultivated plants and particular traits in domesticated animals.
Agricultural Literacy Outcomes
Science, Technology, Engineering & Math
Describe how biological processes influence and are leveraged in agricultural production and processing (e.g., photosynthesis, fermentation, cell division, heredity/genetics, nitrogen fixation) (T4.6-8.b)
Provide examples of science and technology used in agricultural systems (e.g., GPS, artificial insemination, biotechnology, soil testing, ethanol production, etc.); explain how they meet our basic needs, and detail their social, economic, and environmental impacts (T4.6-8.i)
Reason abstractly and quantitatively. Students make sense of quantities and their relationships in problem situations. They bring two complementary abilities to bear on problems involving quantitative relationships: the ability to decontextualize—to abstract a given situation and represent it symbolically and manipulate the representing symbols as if they have a life of their own, without necessarily attending to their referents—and the ability to contextualize, to pause as needed during the manipulation process in order to probe into the referents for the symbols involved. Quantitative reasoning entails habits of creating a coherent representation of the problem at hand; considering the units involved; attending to the meaning of quantities, not just how to compute them; and knowing and flexibly using different properties of operations and objects.
Model with mathematics. Students can apply the mathematics they know to solve problems arising in everyday life, society, and the workplace. Students who can apply what they know are comfortable making assumptions and approximations to simplify a complicated situation, realizing that these may need revision later. They are able to identify important quantities in a practical situation and map their relationships using such tools as diagrams, two-way tables, graphs, flowcharts and formulas. They can analyze those relationships mathematically to draw conclusions.
Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.