Summary
Overview
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.
NGSS Alignment
This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:- MS-LS4-4. 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.
- MS-LS4-5. Gather and synthesize information about technologies that have changed the way humans influence the inheritance of desired traits in organisms.
| Science & Engineering Practices | Disciplinary Core Ideas | Crosscutting Concepts | |||
| Science & Engineering Practices | Obtaining, Evaluating, and Communicating Information.
Obtaining, evaluating, and communicating information in 6-8 builds on K-5 experiences and progresses to evaluating the merit and validity of ideas and methods. Gather, read, and synthesize information from multiple appropriate sources and assess the credibility, accuracy, and possible bias of each publication and methods used, and describe how they are supported or not supported by evidence. |
Disciplinary Core Ideas | LS4.B: Natural Selection.
In artificial selection, humans have the capacity to influence certain characteristics of organisms by selective breeding. One can choose desired parental traits determined by genes, which are then passed on to offspring. |
Crosscutting Concepts | Stability and Change.
For both designed and natural systems, conditions that affect stability and factors that control states of change are critical elements to consider and understand.
Cause and Effect. Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability. - - - - - - - - - - - - - - - - - - - - - - - - - - - Connections to Engineering, Technology, and Applications of Science Interdependence of Science, Engineering, and Technology. Engineering advances have led to important discoveries in virtually every field of science, and scientific discoveries have led to the development of entire industries and engineered systems. - - - - - - - - - - - - - - - - - - - - - - - - - - - Connections to Nature of Science Science Addresses Questions About the Natural and Material World. Scientific knowledge can describe the consequences of actions but does not necessarily prescribe the decisions that society takes. |
Materials Needed
Activity 1:
- Apple Genetics PowerPoint Slides
- Apple Genetics worksheet, 1 per student
- Per group of students:
- 1 Paper Plate
- 1 Whole Braeburn Apple
- 1 Whole Royal Gala Apple
- 1 Whole Jazz Apple
- 1 Knife (or apple slicer to cut apple)
Activity 2:
Essential Files (maps, charts, pictures, or documents)
Vocabulary Words
allele: a variant of a gene
dominant allele: an allele whose trait always shows up in the organism when the allele is present (written as uppercase letter)
gene: a section of DNA that codes for a certain trait
genotype: an organism's genetic makeup or allele combinations
heredity: the passing of traits from parents to offspring
heterozygous: having 2 different alleles for a trait.
homozygous: having two identical alleles for a trait.
phenotype: an organism's physical appearance or visible trait
probability: a number that describes how likely it is that an event will occur
Punnet Square: a diagram used to predict an outcome of a particular cross or breeding experiment
recessive allele: an allele that is masked when a dominant allele is present (written as lower case letter)
trait: a characteristic that an organism can pass on to its offspring through its genes
Did You Know? (Ag Facts)
- Apples are a member of the rose family.1
- More than 2,500 varieties of apples are grown in the United States, but only the crabapple is native to North America.1
- The average person eats 65 apples per year.1
- Apples are 25% air, which is why they float in water.1
Background Agricultural Connections
Prior to this lesson, students should have a basic understanding of inherited traits and know that all cells of an organism have DNA. DNA is the blueprint providing the organism with coded instructions for proper function and development. Students should also know that genes are sections of DNA that are responsible for passing specific traits from parent to offspring. Students will need to be familiar with vocabulary such as phenotype, genotype, homozygous, and heterozygous to successfully complete the lesson and student worksheet and determine probabilities associated with possible offspring using a Punnett Square. Students will be introduced to several varieties of apples and discover how new varieties can be created through crossbreeding.
Key STEM Ideas
Genetics is the study of heredity, while heredity is the passing of traits from parents to offspring. This lesson will help solidify key genetics vocabulary words.
The main idea of this lesson is to show the application of genetic crossing for the benefit of agriculture by producing apples with a variety of traits.
Gregor Mendel was a priest who worked with the genetic crossing of pea plants. He would cross purebred short pea plants with purebred tall pea plants. Through his experiments he determined that some traits were visible in the plant (dominant traits) while others were not, but were still able to be passed on to future generations (recessive traits). Understanding what we see and what the genetic makeup of an organism is can be quite different. When you look at an organism, its physical characteristics are all dependent on a specific allele combination. This is the difference between phenotype and genotype. Students will use Punnett Squares in this lesson to help determine all the possible allele combinations in a genetic cross and their probabilities.
Crossbreeding allows breeders to create better quality apples by incorporating traits from two parent plants into the seeds of a new generation of plants. Breeders must understand both genotypes and phenotypes to accomplish this task. Breeders must also decide which traits are desirable and should be selected. This is an intensive process that involves breeding successive generations of apples with the preferred traits in order to get the final product. There are several crop modification techniques breeders use to develop new plant/fruit varieties.
Connections to Agriculture
Apples are an important agricultural crop. There are about 7,500 apple producers in the United States. Washington, New York, and Michigan are the leaders in apple production. Growers produce a variety of different kinds of apples. Some apples are better for baking while others are typically consumed fresh. Apples are a good snack choice as they satiate hunger, contain no fat and relatively few calories while being high in fiber and vitamin C.
Apples are grown through a process called grafting rather than being grown from seed. This is done because most apple varieties are self-unfruitful, which means their blossoms must be fertilized with the pollen of a separate variety in order to produce fruit. The fruit has traits from the parent tree, but the seeds inside will be a cross of the two varieties. This mixture of genetic material in the seeds means the grower won’t know what traits a tree grown from these seeds will have and what the resulting fruit will taste like.
To avoid this uncertainty apple growers do not grow new trees from seed. Instead, new apple trees are propagated through a process called grafting. In this process a special cut is made into the rootstock of a tree. Then, they graft or transplant a section of a stem with leaf buds called a scion from a variety that has desirable traits into the cut. In time the two pieces fuse together allowing for growth of the scion. Eventually, blossoms on the scion will be pollinated and will produce a consistent variety of fruit with the desired traits.
The goal of apple breeding is to continuously produce quality apples with desirable traits. Cross breeding and genetic engineering are two methods that have allowed breeders to produce better quality apples. See Crop Modification Techniques)
Interest Approach - Engagement
- 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 some of the most commonly sold apples. In the United States those include Red Delicious, McIntosh, Golden/Yellow Delicious, Gala, Granny Smith, Fuji, Braeburn, Pink Lady, Honeycrisp, Empire, Opal, and Jazz. 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.
Procedures
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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. Phenomenon-Based Question: What makes apple varieties different? |
| Question | Science and Engineering Practices | Student Engagement in Practices | Explanation |
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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. |
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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. |
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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.
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?
- To discover the answer, show the Have We Engineered The Perfect Apple? video:
- 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.
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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?
- Why do most apples get brown after cutting (see the Fruits Gone Bad? Discover Enzymatic Browning activity), but Opal apples and Arctic® apples do not?
Enriching Activities
- 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.
- Watch the Honeycrisp vs Red Delicious - How We Finally Got Good Apples video:
- Listen to the NPR podcast "The Miracle Apple."
Sources
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.
Ag Fact Sources:
- Apples and More, © 2021 University of Illinois Extension.
Author
Kevin Atterberg, Erin Ingram, Molly Brandt, Andrea Gardner, and Debra Spielmaker
Organization Affiliation
National Center for Agricultural Literacy
