Contents

Week 21: Meiosis and Chromosomal Inheritance

Teaching Meiosis

If you’re following this scope and sequence, then you’ve finished unit 6 (I do unit 6 before unit 5). That sets you up to start unit 5, Heredity. As the College Board suggests, I start with Meiosis (Topics 5.1 and 5.2) but then jump to Topic 5.6 (Chromosomal Inheritance). Next week, we’ll jump back to Mendelian and post-Mendelian genetics, which comes in between.

Stitching that all together, here are the College Board’s learning objectives for this unit, reframed in a student and teacher friendly format.

College Board Learning Objectives for Meiosis

  1. TOPIC 5.1: Meiosis
    1. Explain how meiosis transmits genetic material from one generation to the next.
    2. Compare and contrast diploid and haploid cells, and explain how these terms connect to somatic cells and germ cells.
    3. Compare and contrast mitosis and meiosis (the types of daughter cells, the number of cell divisions)
  2. Topics 5.2 and 5.6: Meiosis and Genetic Diversity
    1. Explain how meiosis generates genetic diversity.
    2. Define “homologous” chromosomes (their origin, their relationship in term of genetic information) and explain what happens to homologous pairs during meiosis (independent assortment).
    3. Explain what crossing over is, and how it generates genetic diversity.
    4. Explain fertilization (in terms of haploid and diploid chromosome numbers), as well as fertilization’s contribution to genetic diversity.
    5. Compare meiosis 1 and meiosis 2, and explain what happens during each process.
    6. Connect the events of meiosis and fertilization to how sexual reproduction creates variation.
    7. Explain how certain aspects of human genetic variation (Down’s syndrome, etc.) can be explained by chromosomal changes resulting from meiosis (nondisjunction).

Meiosis and Chromosomal Variation tutorials on Learn-Biology.com

If you have your students complete our module about Meiosis on Learn-Biology.com, you can ensure that your students will master all of these objectives. Your students can use this  Meiosis Student Learning Guide to guide them through the materials. Note that you can also use this student learning guide as a review sheet and for checking for understanding.

Here’s an overview of what’s in the tutorials.

1. Meiosis: Basic Concepts

This tutorial will teach your students the difference between haploid and diploid cells, and the meaning of the term homologous in the context of meiosis and chromosomes.

2. Meiosis 1 v. Meiosis 2

In this tutorial, your students will come to understand how meiosis, fertilization, and mitosis fit into the life cycle of sexually reproducing organisms, like us. This is captured in the diagram below.

Students will also learn to distinguish between meiosis 1 and meiosis 2, and to be able to compare and contrast mitosis and meiosis, as shown in this diagram.

3. How Meiosis Creates Variation and 

4. Topics 5.1 – 5.2, Part 4: Meiosis, Step by Step

Our third and 4th tutorials focus on the two key processes by which meiosis creates variation: independent assortment of chromosomes, and crossing over, which creates newly recombinant chromosomes in every generation. By the end of tutorial four your students will be able to talk, write and think their way through diagrams like this:

5. Topic 5.6, Part 1: Sex Determination and 

6. Topic 5.6, Part 2: Part 2: Nondisjunction and Human Chromosomal Variation

Meiosis explains some of the basic facts of life: like why births are approximately 50/50 male and female. Tutorial 5 takes on sex determination in mammals (the XX/XY system). It also addresses the ZZ/ZW system in birds, temperature-dependent sex determination in certain reptiles, and haplodiploidy in certain insects.

Tutorial 6 looks at nondisjunction and its consequences: Down Syndrome, Klinefelter Syndrome, XYY, and Turner Syndrome. It also includes a cumulative set of flashcards about meiosis and related topics and a Multiple Choice Speed challenge.

Other resources:

My Meiosis Song can help you teach a surprising amount of the material above. Here’s how it starts:

Meiosis is how make sex cells or gametes,
The sperm cells or egg cells performing the feat,
Of moving genes forward in eukaryotes like orchids and bees,
Meiosis doesn’t happen in all cells of the body,
There’s just a few cells that have hobby,
I’m talking ’bout germ cells in testes and ovaries.
The video (linked above) is great for review, or even for a preview. You can show it at the start of the unit, accompanied by some big-picture questions like:
  1. You inherit half of your genes from your mother and half from your father. Try to describe how you think that might work. Which half?
  2. If you have one, think of your sibling. If you don’t, think of any pair of siblings that you know. How genetically similar are siblings?
  3. Humans, like all sexually reproducing beings, expend a lot of energy trying to find mates and pass on their genes. Why do most multicellular eukaryotes reproduce sexually, instead of just cloning themselves?

For a group activity, there’s a Meiosis POGIL, but it’s not in the AP set of POGILS: it’s in the high school set. You can buy POGILS from Flinn Scientific. Note that this is one of a few POGILs from the high school set that I use, so you have to decide if it’s worth the investment (the AP Bio ones definitely are).

In terms of labs, the one that’s recommended by the College board is the Sordaria lab. (the link goes to the College Board’s AP Bio lab manual). To understand the underlying biology (which can be fairly tricky and often misunderstood), please look at this page on my website. 

Depending on how comfortable you are working with fungi, you can breed the various strains together yourself, or you can buy pre-inoculated plates from companies like Carolina or Flinn. An even easier route is to just buy Sordaria cards, which are sold by Flinn.

Week 22 and 23: Heredity (Topic 5.3 – 5.5)

Teaching Heredity

It takes me about two weeks to teach genetics. Note that my previous meiosis unit includes topics like nondisjunction, so I’m talking about two weeks to cover standards 5.3, 5.4, and 5.5. Add to that the one week it takes to teach meiosis, and you should be able to get through all of Unit 5 in about 3 weeks.

College Board Learning Objectives for Genetics

Here’s a link to the College Board’s learning objectives for all of Unit 5. 

Here’s a list of objectives that are more student (and teacher) friendly.

  1. Topic 5.3: Mendelian Genetics
    1. Explain Mendel’s laws of segregation and independent assortment, and connect them to what happens during meiosis.
    2. Explain relevant rules of probability that apply to genetics. The rule of multiplication is the most important of these.
    3. Be able to solve genetics problems involving
      1. monohybrid and dihybrid crosses with autosomal genes;
      2. blood type (A, B, O system). Note that this while blood type isn’t in the College Board’s standards, you can use it to teach about inheritance patterns with multiple alleles.
  2. Topic 5.4: Post Mendelian Genetics
    1. Explain the chromosomal basis of linkage and recombination. When given data about linkage, be able to determine the distance (in map units) between linked alleles.
    2. Explain the inheritance patterns of sex-linked genes, and be able to solve genetics problems involving sex linkage.
    3. Explain non-XY sex determination systems, such as the ZZ/ZW system in birds, haplodiploidy in bees, and temperature-dependent sex determination in certain reptilian clades.
    4. Define polygenic traits, and describe why these usually have a bell-curve-shaped distribution pattern.
    5. Explain non-nuclear inheritance (via mitochondria, chloroplasts, etc.)
  3. Topic 5.5: Environmental Effects on Phenotype
    1. Explain how the interaction between genotype and environment is a major determinant of phenotype.

Genetics tutorials on Learn-Biology.com

Learn-biology.com organizes online learning about genetics into six tutorials, supported by this student learning guide.

Topics 5.3 – 5.5, Part 1: Mendelian Genetics and Punnett Squares

Using the example of sickle cell anemia, this introductory tutorial will teach basic genetics vocabulary (dominant, recessive, phenotype, genotype, etc). It also walks your students through how to solve genetics problems using Punnett squares.

Topics 5.3 – 5.5, Part 2: Solving ABO Blood Type inheritance problems

In this tutorial, I introduce the idea of codominance and multiple alleles. This topic is not explicitly in the standards, but how can you not teach about blood type?

Topics 5.3 – 5.5, Part 3: Sex-linked alleles, and a few other human genetic conditions to know. 

This tutorial covers

  1. Sex-linkage in humans, focusing on hemophilia.
  2. Other sex-linked conditions like Red-Green Colorblindness, Duchenne’s Muscular Dystrophy, and white eye color in fruit flies.
  3. How to use Punnett Squares to solve genetics problems involving sex linkage.
  4. Sex-linked alleles in birds
  5. A brief survey of six genetic conditions that AP Bio students should be familiar with: sickle cell anemia, cystic fibrosis, hemophilia (and other sex-linked conditions), Huntington’s disease, and achondroplasia.

Topics 5.3 – 5.5, Part 4: Dihybrid Crosses

After doing this tutorial, your students will know how to set up and solve dihybrid crosses.

Topics 5.3 – 5.5, Part 5: Linkage and Recombination

Linked genes and determining recombination frequencies. Along the way, your student will get a deep understanding of how linkage is different from independent assortment.

Topics 5.3 – 5.5, Part 6: How to do the χ2 (Chi Squared) Test

A step-by-step walkthrough everything your students need to understand in order to do chi square analysis of results from genetic crosses.

Topics 5.3 – 5.5, Part 7: Mitochondrial Inheritance, Incomplete Dominance, and Genotype-Environment Interaction

All of the topics above.

Teaching genetics in the classroom

There are a lot of breeding simulations, but I don’t use them. The way to get to mastery of genetics is for students to solve LOTS of genetics problems, and that’s my main focus.

As students solve these problems, I encourage them to use these six steps for solving genetics problems (which are modeled in the tutorials).

  1. Write the genotypes of the parents.
  2. Draw a Punnett square.
  3. Put the possible alleles of the gametes on the top and side of the square.
  4. Bring the alleles of possible gametes together.
  5. Show the genotype ratio.
  6. Show the phenotype ratio.

As students get better at solving problems, they can back off on some of these steps (and some would be ridiculously redundant and time-consuming in certain situations, like dihybrid crosses).

Here’s what I use.

  • Here’s a set of beginning-level genetics problem sets that you can use to help your students master the material in the first four tutorials. Note that the last pages have all the solutions (I find that giving out the solutions makes instruction much easier and more successful). Keep in mind that my students did not take a 9th-grade biology course, so these might be too easy for your students.
  • For more advanced problems, I go to my textbook…Campbell, Biology in Focus. While I don’t use the text (because I use Learn-Biology.com, which I hope is true of you as well!), I do use the problem sets for Chapter 11 and Chapter 12. The textbook provides answers in the appendix. I spend a fair amount of time both working on these problems in the classroom and having my students work on them (usually in groups).
  • For pedigree analysis, I use this worksheet.

Resources for Unit 5 Review

A cumulative review of Unit 5 is available at Unit 3 Cumulative Objectives, Flashcards, and Quizzes

In addition, use the College Board’s resources on AP Classroom, particularly their progress check questions.

Links