Lesson Plan

Objectives

In this lesson, students discover how heredity follows certain patterns based on the laws of probability. Students will learn how Mendel’s experiments with garden peas began the study of genetics. They will also learn to solve genetics problems using Punnett squares and determine phenotypic and genotypic ratios. Students will:

  • differentiate between alleles, genes and chromosomes.
  • state Mendel’s Laws of Inheritance and apply them when solving genetics problems.
  • predict the offspring of a genetic cross using a Punnett square.
  • differentiate between incomplete dominance and codominant alleles.
  • explain how multiple alleles and polygenic traits increase variation in the population.
  • recognize sex-linked genes.
  • recognize linked and nonlinked genes.

Essential Questions

Vocabulary

  • Alleles: Forms of genes responsible for controlling the same trait; different versions of the same gene.
  • Autosome: A chromosome that is not a sex (X or Y) chromosome.
  • Codominant: Alleles that are fully expressed in the heterozygous condition.
  • Dominant Allele: An allele that is always expressed when it is present in an individual.
  • Gene: The fundamental, physical, and functional unit of heredity.
  • Hybrid: Offspring produced from a cross between two purebred organisms.
  • Incomplete Dominance: Traits in which the heterozygote shows a different phenotype from the homozygous dominant phenotype.
  • Phenotype: The physical characteristics of an organism.
  • Polygenic: Traits in which several genes contribute to the overall phenotype.
  • Recessive: An allele that is only expressed when the dominant allele for a trait is not present.
  • Sex-linked Traits: Phenotype of an allele located on a sex chromosome.
  • Trait: A specific characteristic that varies from one individual to another.
  • Genotype: The genetic makeup of an organism.
  • Heredity: The passing of genetic factors from parent to offspring.
  • Heterozygous: Having dissimilar alleles that code for the same gene or trait. 
  • Homozygous: Having two identical alleles that code for the same trait.

Duration

At least one week

Prerequisite Skills

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Materials

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Formative Assessment

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    • During directed instruction, provide corrections and feedback as students respond to questions and discuss answers over the new material.
    • Listen carefully and offer redirection, corrections, or praise to students as they pair and share answers with the class during directed instruction.
    • Feedback and corrections are provided as students work through sample genetics problems during guided instruction.
    • You will provide feedback to students on their genetics problems worksheets.

Suggested Instructional Supports

  • View
    Scaffolding, Explicit Instruction
    W: This lesson focuses on the patterns of heredity and the laws of probability to predict the offspring of genetic crosses. Students are evaluated on their responses to questions during the lessons and on practice problem worksheets.
    H: Rolling number cubes and relating the probable outcomes to genetics introduces this lesson. Dominant and recessive traits are related to a few human traits that are easy for students to identify. Whenever possible, human genes and alleles are used as examples.
    E: In order to understand genetics, it is imperative that students know the difference between dominant and recessive alleles. Students identify traits in themselves and determine whether they have the dominant and recessive allele for that trait.
    R: Imbedded within the PowerPoint, students are given “Think-Pair-Share” questions. The questions give students the opportunity to apply new concepts and reflect on new learning. As you review the answers with the class, students are able to rethink their own answers in light of other students’ responses.
    E: Students express their thoughts and reasons during the “Think-Pair-Share” portion of the activity. This allows them the opportunity to assess their partner’s ideas and their own.
    T: Students moving beyond the standards may benefit from performing a virtual genetics lab. Students who need extra practice with dominant and recessive traits, and relating genetics to everyday life, can make a pedigree chart of a trait explored in class.
    O: This lesson begins with a historical perspective of Mendel’s experiment and conclusions. It progresses from simple genetics problems to more challenging problems. The lesson concludes with genetics problems that do not seem to follow Mendel’s rules.

Instructional Procedures

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    Introduce the lesson by writing on the board:

     

    “Chance favors the prepared mind.”

    —Louis Pasteur

     

    Explain and give a few examples of how to use the product law and the sum law to determine probability:

    The product law states that the probability of two independent events occurring simultaneously is equal to the product of the probabilities of each event occurring alone.

    Product Law Example:

    What is the probability of a coin toss resulting in 2 consecutive heads?

    Lead students to understand: The probability for each toss individually resulting in heads is 1/2. To obtain the probability of two consecutive heads, multiply their individual probabilities.  1/2 × 1/2 = 1/4.

    The sum law states that the probability of one or the other of two mutually exclusive events occurring is equal to the sum of the probability of each event occurring alone.

    Sum Law Example:

    What is the probability if we flip a coin twice, that it will result in heads one time, and tails the next, if we do not specify the order in which they come?

    Lead students to understand: There are two mutually exclusive ways this can occur:

    • Heads the first time, tails the second.
    • Tails the first time, heads the second.

    The probability for each event is 1/2.

    The probability of each situation can be derived using the product law: 1/4 × 1/4 = 1/2 .

    Since the individual events are mutually exclusive, the total probability of either occurring can be derived using the sum law: 1/4 × 1/4 = 1/2.

     

    Give each group of students a pair of number cubes. Ask, “What are the chances of you rolling double sixes on the first roll?” Have students roll the number cubes to see which groups, if any, can roll double numbers on their first roll. After discussing their results, ask, “Is there a better way of determining the odds?” Brainstorm and discuss potential methods. Have students roll the number cubes ten times, recording what number was rolled. Make a chart on the board and have students report their findings. Ask, “What number was rolled most often? Why?” Seven should be the number rolled most often. Show students why this is so by writing the chart on the board with all the possibilities.

     

     

    Roll of Number Cube 1

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    Roll of Number Cube 2

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    Explain that there are 6 out of 36 possibilities of rolling a 7, while there is only 1 out of 36 possibilities of rolling a 12. Discuss the ratios for all the possible rolls and discuss how their data matches the statics from the table. If their data does not mirror the projected outcomes, explain that as the sample increases, the closer the actual ratios are to the theoretical. “How can we make our data look more like the probable outcomes?” (roll the number cubes more)

    Part 1: People Search Activity (1 day)

    Provide background information for the traits used in the People Search activity. Explain each of the dominant and recessive traits from the activity. Photos of the traits can be found at “Comparing Inherited Human Traits” available at http://www.sdawis.org/files/Outreach/traits_compairing.pdf.

    Introduce dominant and recessive traits, and hand out the People Search worksheet for students to work on in pairs (S-B-8-1_People Search.doc).

    Part 2: Mendelian Genetics (2–3 days)

    Have students take notes from the Heredity PowerPoint presentation (S-B-8-1_Heredity PowerPoint.ppt). The PowerPoint slides have minimal information, so students need to listen to the lecture and write information as much as they can.

    After reviewing how to solve simple genetics problems with one trait, have students work on Genetics Problems 1 in class or as homework (S-B-8-1_Genetics Problems 1 and KEY.doc).

    Finish the notes on Mendelian Genetics. Review solving problems involving two traits and have students work on Genetics Problems 2 in class or as homework (S-B-8-1_Genetics Problems 2 and KEY.doc).

    Part 3: Non-Mendelian Genetics (2–3 days)

    Have students draw a picture of an eye and try to color it with the same colors they see in their own eye (if mirrors are available) or their neighbor’s eye. Ask:

    • “How many different heights do we see in adults?” (There are many different heights.)
    • “Do you think one gene with only two alleles is responsible for this kind of variation?” (Answers will vary but highlight that height is a polygenic trait, produced by the interaction of many genes.)

    Have students take notes from the Non-Mendelian Heredity PowerPoint (S-B-8-1_Non-Mendelian Heredity PowerPoint.ppt). As with other PowerPoint presentations, students will need to listen to the lecture and write information as much as they can, over and above the words that appear on the slides.

    After a review of how to solve non-Mendelian problems and problems using pedigree charts, have students work on Genetics Problems 3 in class or as homework (S-B-8-1_Genetics Problems 3 and KEY.doc).

     

    Extension:

    • Students who may be going beyond the standards may benefit from performing and analyzing a virtual lab found at www.mhhe.com/biosci/genbio/virtual_labs/BL_15/BL_15.html. Have students write a lab report when they have completed the experiment.
    • Students who need an opportunity for additional learning can create a pedigree chart for a specific trait discussed in class (rolling tongue, widow’s peak, etc.). Go back as many generations with as many members of the family as possible.

Related Instructional Videos

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DRAFT 05/26/2011
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