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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.
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
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. For more information and pictures of the grafting process, please visit the website Apple Tree Propagation: Grafting.
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.
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
|Question||Science and Engineering Practices||Student Engagement in Practices||Explanation|
||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.|
||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.|
||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)
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 rates of change are critical elements to consider and understand.
Activity 2: Apple Genetics - Keeping Them the Same (Episode Question 3)
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:
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!
Show the 4-minute video clip, Have We Engineered The Perfect Apple? to see the science behind the taste of the Honeycrisp apple.
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.
Listen to the NPR podcast "The Miracle Apple."
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.
Ag Fact Sources:
Kevin Atterberg, Erin Ingram, Molly Brandt, Andrea Gardner, and Debra Spielmaker
National Center for Agricultural Literacy