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. Grades 6-8

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 unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring

genotype: the genetic makeup of an organism

heredity: the passing of traits from a parent to its offspring

heterozygous: having two different alleles for a trait

homozygous: having two identical alleles for a trait

phenotype: the set of observable characteristics of an organism resulting from the interaction of its genotype with the environment

probability: a number that describes how likely it is that an event will occur

Punnett 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: observable, physical characteristic obtained through genetic inheritance

This lesson can be nested into a storyline as an episode exploring the phenomena of taste and other characteristics that can be observed in apples. In this episode, students investigate the question, "What makes apple characteristics different?" Phenomena-based lessons include storylines which emerge based upon student questions. Other lesson plans in the National Agricultural Literacy Curriculum Matrix may be used as episodes to investigate student questions needing science-based explanations. For more information about phenomena storylines visit nextgenstorylines.org.

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)

This lesson has been adapted for online instruction and can be found on the 6-8th grade eLearning site.

1. 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.
2. 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.
3. Ask students if they know how these different apple varieties became available.
4. 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. Phenomenon-Based Episode: What makes apple varieties different? Disciplinary Core Ideas: Growth and Development of Organisms National Agricultural Literacy Outcome Theme: Science, Technology, Engineering, and Math Phenemona Table- Apple Genetics

Activity 1: Apple Genetics - Making them Different (Episode Questions 1 and 2)

1. Give each student one copy of the Apple Genetics activity sheet. Divide the class into small groups of students (2-4).
2. 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)
3. 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.
4. Have students complete "Part 1" and "Part 2" of the worksheet and then stop.
5. Project the Apple Genetics PowerPoint slides 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.
6. Use slide 3 of the PowerPoint to review vocabulary if needed. Make sure students are familiar with the terms.  
7. 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.
8. 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. 
9. 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.
10. Talk about the concept of crossbreeding and how it is used to produce better quality organisms (slide 8).
11. Explain that the Honeycrisp apple (slide 9) was also developed by crossbreeding, and is a competitor of the Jazz apple.
12. 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.

Three Dimensional Learning Proficiency: Crosscutting Concepts Students engage in scientific investigation as they investigate and build models and theories about the natural world. 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.

Activity 2: Apple Genetics - Keeping Them the Same (Episode Question 3)

1. 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.
2. 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?
3. To discover the answer, show Apple - How Does it Grow? 
4. 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).
5. 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.)
6. 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.

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? 

1. http://www.care2.com/greenliving/22-fun-facts-about-apples.html
2. https://extension.illinois.edu/apples/facts.cfm

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.

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• Genetic Science Learning Center
• Have We Engineered the Perfect Apple? video
• How CRISPR Lets You Edit DNA
• How Mendel's Pea Plants Helped Us Understand Genetics
• Making a New Apple Cultivar
• Phenomenon