Single Trait Crosses. Activity Overview. Essential Questions. Objectives. Introduction. Materials and Resources

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1 Single Trait Crosses Grade Range: High School Key Terms Lesson Time: 40 minutes Materials and Resources Allele Dominant Emoji Gamete Genetics Genotype Law of Dominance Law of Segregation Monohybrid Phenotype Recessive Traits Modeling Inheritance with Emojis Worksheet Textbook, printed materials, and/or the Internet zview Activity Overview Who was Gregor Mendel and why is he so important? This famous scientist conducted experiments that provided insights into inheritance that launched a new field of study called genetics. Modern genetics is the study of heredity and the variation of inherited characteristics. Students will learn how to determine the probable outcomes of different single-trait crosses. Essential Questions 1. How are traits inherited from previous generations? 2. Why is there variation in traits? Objectives Learn vocabulary used to describe genetics and inheritance Review the Law of Segregation Review the Law of Dominance Investigate pea plant characteristics Determine probable outcomes of different single-trait crosses Introduction Prior to beginning this activity, students must either complete Mendel s Pea Plants in Studio or already have an understanding of Mendel s experiments with pea plants. To start the activity, review the vocabulary terms related to genetics with the students. Direct students to work with a partner to complete the Modeling Inheritance with Emojis Worksheet, where they will model the pattern of inheritance from parent to offspring. Remind the students to practice using the vocabulary terms as they discuss the worksheet with their partner. Once students have created their Emoji, explain that they will practice determining the probable outcomes of genetic crosses that involve one trait zspace, Inc. All Rights Reserved Single Trait Crosses 1

2 Teacher Note: It is best for students to work with a partner throughout this lesson so that they can discuss the information and practice the vocabulary of genetics. zspace Activity Activity Questions Provided in Studio Answers may vary. Sample answers are provided below. 1. Gregor Mendel performed his experiments with pea plants from , but it was not until after Mendel s death, in 1884, that scientists revisited Mendel s data and used his theories to launch a new field of study called genetics. The focus of modern genetics today is to study genes, inheritance, and genetic variation. Mendel observed thousands of pea plants. Other scientists used different organisms to repeat his experimental observations and support Mendel s theories. 2. Mendel s ideas have come to be known as Mendel s Law of Segregation, Law of Dominance, and Law of Independent Assortment. In science, a law always applies under the same conditions. Let s start by investigating traits that follow Mendelian inheritance. This means that these traits will always demonstrate inheritance that follows Mendel s Laws. Observe these models and describe one trait for each. The pea plant models show height, flower location, and pea pod color. The pea pod model shows pod color, pea color, and pea shape. 3. Mendel made an excellent choice by using pea plants as his experimental organism. Not only are pea plants easy to maintain, needing only sunlight, soil, and water to grow, but they are also very easy to manipulate and control. How was Mendel able to control the reproduction of the pea plants? Mendel removed the male reproductive structures from some flowers and the female reproductive structures from other flowers. He used a paintbrush to transfer pollen from one plant to another. 4. Mendel dissected the pea flowers; these models show what he would have done. Notice that this produces male and female gametes. Add a Note to identify the male and female reproductive structures. Then take a photo. Mendel used a paintbrush to transfer pollen from one flower to another. What is the name of this process? Why was this process critical to his experiment? Mendel cross-pollinated the flowers instead of letting the flowers self-pollinate. In this way, Mendel could be in charge of the reproduction of the pea plants. Photo showing male and female reproductive structures with Note. 5. These two parent pea plants have differently colored flowers. What are the different possible outcomes for the flower color of the offspring of these parent plants? Hint: In order to determine the probable outcome of the offspring, you must remember what Mendel said about dominant and recessive alleles in his Law of Dominance. Hint: What color flowers might their offspring have? The offspring could either have white flowers or purple flowers. 6. Here are the genotypes of each parent. Each parent will only pass on one allele to each of their offspring following Mendel s Law of Segregation. You can see the plants have been labeled with the two possible alleles that they could pass on to their offspring. What does the Law of Segregation say will happen to these two alleles? The Law of Segregation states that the two alleles will separate so that only one allele for this trait will be in each gamete. 7. Open the Model Gallery in your Backpack and add the correct model of the offspring that would result from this cross. Use the right stylus button to Resize your model and make it smaller. Then take a photo. Photo should include a purple flower zspace, Inc. All Rights Reserved Single Trait Crosses 2

3 8. This cross only involved one trait, flower color. In a cross between two homozygous parents, each parent can only give one type of allele to the offspring because of Mendel s Law of Segregation. All the offspring will be heterozygous and will have purple flowers because of Mendel s Law of Dominance. 9. Let s try another problem. Here are a homozygous recessive, white-flowered parent and a heterozygous, purple-flowered parent. What are the probable outcomes for their offspring? Use Notes above the plants to label the genotype of each parent. Use Notes underneath the plants to show the possible alleles passed on by these parents. Open the Model Gallery in your Backpack and add the correct models of the offspring that could result from this cross. Remember to Resize your models. Then take a photo. Hint: Remember that when you created your Emoji, each parent could give either allele to the offspring. There are four possible combinations of how these alleles may join together to create offspring. Photo should include Notes above the white flower with genotype pp and the purple flower with genotype Pp, Notes below the white flower with one p allele being passed on and the purple flower with a p or P being passed on to the offspring, and two additional models: one white flower and one purple flower. 10. When a homozygous recessive parent and a heterozygous parent are crossed, some offspring will be purple and some offspring will be white. What percentages of purple offspring and white offspring would you expect? Defend your answer with data. Hint: When you created your Emoji, what were the chances your Emoji would receive the dominant or recessive allele when you flipped the coin? 50% of the offspring will have white flowers and 50% will have purple flowers. 11. This next cross is called a monohybrid cross. The two parents are both heterozygous for the same single trait of flower color. 1. Use Notes above the plants to label the genotype of each parent. 2. Use Notes underneath the plants to show the possible alleles passed on by these parents. 3. Open the Model Gallery in your Backpack and add the correct models of the offspring that could result from this cross. Remember to Resize your models. 4. Use Notes underneath the offspring to label the genotype for each. 5. Then take a photo. Photo showing: 1. Notes above the purple parent flowers with Pp genotypes. 2. Notes under the purple parent flowers with a p or P being passed on to the offspring. 3. Three additional models added: two purple flowers and one white flower. 4. Notes underneath the offspring with one purple flower labeled PP, one purple flower labeled Pp, and one white flower labeled pp. 12. Mendel observed thousands of pea plants. When he focused on monohybrid crosses, Mendel determined a specific ratio that would predict the probable outcome of the genotypes and phenotypes of the offspring. The genotype ratio was 1:2:1 and the phenotype ratio was 3:1. Look at the bottom row of offspring. Read through the data and use the data to describe how Mendel determined his ratio. Mendel observed that one out of four or 25% of the offspring would be PP, two out of four or 50% of the offspring would be Pp, and one out of four or 25% of the offspring would be pp. This was the genotype ratio. Mendel also observed that three out of four or 75% of the offspring would produce purple flowers because purple is the dominant allele. One out of four or 25% of the offspring would produce the recessive phenotype, white flowers. 13. The ratios are important to know. If you are observing inheritance and the offspring follow Mendel s ratios, then you can predict that the traits also follow Mendel s Laws. If the offspring do not follow Mendel s ratios, then there is a different type of genetic interaction being observed that is an exception to Mendel s Laws. As you advance in your studies of genetics, you will be introduced to some of these exceptions. 14. Review the information covered in this lesson. Be sure that you can clearly describe Mendel s Laws of Segregation and Dominance. You should be able to define the important vocabulary terms for genetics and use them as you discuss the information with your partner and your class zspace, Inc. All Rights Reserved Single Trait Crosses 3

4 Closing Questions for Discussion 1. How does Mendel s Law of Segregation help explain how genetic traits are inherited? Each parent has two alleles, but will only pass one allele onto their offspring. 2. How does Mendel s Law of Dominance help explain how genetic traits are inherited? Some alleles are dominant and will mask recessive alleles. In order for a recessive phenotype to appear, the organism must have two recessive alleles. Use zview to show pea plant models that exhibit different traits such as height, flower location, color of pods, color of peas, and seed shape. Provide students with the data table below. Ask them to predict the possible outcomes of various crosses and to explain how to determine the probable outcome of a single-trait cross using the vocabulary terms for genetics. Example questions for this discussion are provided below. More Example Single-Trait Crosses to Discuss Trait Dominant Recessive Height of Plant Tall Short Flower Location Axial Terminal Color of Pods Green Yellow Color of Peas Green Yellow Seed Shape Round Wrinkled 1. Choose any trait. What would be the probable outcome of a cross between two homozygous dominant plants? All of the offspring would have the homozygous dominant genotype and the dominant phenotype for that trait. 2. Choose any trait. What would be the probable outcome of a cross between one homozygous dominant plant and one heterozygous plant? 50% of the offspring would have a homozygous dominant genotype, and 50% of the offspring would be heterozygous. All offspring would show the dominant phenotype. 3. Choose any trait. What would be the probable outcome of a cross between two heterozygous plants? 25% of the plants would have a homozygous dominant genotype. 50% of the plants would have a heterozygous genotype. 25% of the plants would have a homozygous recessive genotype. 75% of the plants would show the dominant phenotype. 25% of the plants would show the recessive phenotype. 4. Choose any trait. What would be the probable outcome of a cross between two homozygous recessive plants? All of the offspring would have the homozygous recessive genotype and the recessive phenotype for that trait. 5. Choose any trait. What would be the probable outcome of a cross between one heterozygous plant and one homozygous recessive plant? 2017 zspace, Inc. All Rights Reserved Single Trait Crosses 4

5 50% of the offspring would have a homozygous recessive genotype and the recessive phenotype. 50% of the offspring would be heterozygous and show the dominant phenotype. Extension Activity: Practice using Punnett Squares to determine probable outcomes of genetic crosses by using an online tool, worksheet, or questions from the textbook. Extension Activity: Write their own word problems for classmates to solve. Follow-Up Activity: Crossing Two Traits - Studio Differentiation Group students heterogeneously to allow students with a strong command of the English language to assist in reading or interpreting questions Provide paper copies of diagrams for students to use as a reference Provide a handout with a list of vocabulary terms and definitions that will appear in the activity Have students work as partners or in small groups Use text-to-speech if needed Enrichment: Students could change an additional variable in the activity and look for patterns Enrichment: Students could work on the discussion questions and lead the class discussion Enrichment: Students could build a model of a key concept 2017 zspace, Inc. All Rights Reserved Single Trait Crosses 5