Meiosis

Warm Up: Monday, 11/26/12 Objective: Students will be able to predict which phases of Meiosis are most important and determine the consequences when there is a mistake during Meiosis. Warm Up: What is the purpose of Meiosis? What is the result of Meiosis? (Hint: See your notes about Meiosis or turn to page 276.) Sentence Starter: The purpose of Meiosis is ….

Think, Turn, Talk What is the purpose of Meiosis? What is the result of Meiosis? Partner A: The purpose of Meiosis is __________. Partner B: The result of Meiosis are ____________. The purpose of meiosis is to reduce the number of chromosomes in a cell in half so that during fertilization the zygote created will be diploid. The result of Meiosis are four nonidentical haploid cells. Random Call: Three students to share the purpose and three to share the results.

Meiosis Notes Continued…. Unicellular Organisms (Prokaryotes or Bacteria cells) reproduce through asexual reproduction called binary fission (Mitosis) – making an exact replica of themselves These cells will only undergo Mitosis Multicellular Organisms (Eukaryotes) – reproduce through sexual reproduction (Meiosis) Require haploid cells

CFU: This is a picture of binary fission also called mitosis. Which type of organisms reproduce through mitosis?

Meiosis Notes Continued… CFU: (HOTS) Show me with your fingers. Which of the following statements are true? There are more than one answer. Somatic Cells undergo Mitosis ONLY. Gametes undergo Meiosis ONLY. Somatic Cells undergo Mitosis and Meiosis. Gametes undergo Meiosis and Mitosis. Multicellular Organisms have two different categories of cells: -Somatic Cells (body cells, Ex: liver cells, heart cells, skin cells, muscle cells, eye cells, etc.) -Gametes (sex cells, Ex: sperm and eggs) These cells will under go Meiosis then Mitosis *All cells undergo Mitosis in multicellular organisms CFU: (HOTS) Somatic cells do not undergo Meiosis. Why do you think this is the case? Be ready to share. Remember that the purpose of Meiosis is to cut the number of chromosomes in half so that after fertilization, the zygote will be diploid.

Meiosis Continued… Meiosis I Interphase – DNA is replicated

Prophase I Homologous Chromosomes line up -A pair of chromosomes containing the same sets of genes One chromosome from each parent Don’t necessarily contain identical genetic material Ex. You get one chromosome #4 from mom and one chromosome #4 from dad Crossing Over occurs -Process by which non-sister chromatids from homologous chromosomes exchange genes -CREATES GENETIC VARIABILITY

Homologous Chromosomes line up. Crossing Over CFU: (Pair Share) What is genetic variability? How is genetic variability created? Partner A: Genetic variability is ______________. Partner B: Genetic variability is created by ______________. The purpose of crossing over is to create genetic variability.

Metaphase I Homologous Chromosomes line up in the middle

Write down one thing that is occurring in each phase. Anaphase I Telophase I Write down one thing that is occurring in each phase. Random Call: Two students to share what they wrote.

Write down one thing that is occurring in this phase. Meiosis II Prophase II There are now two cells!!! Write down one thing that is occurring in this phase.

Write down one thing that is occurring in this phase. Metaphase II Write down one thing that is occurring in this phase. Random Call: Two students to share what they wrote.

Anaphase II Sister chromatids separate

Write down one thing that is occurring in this phase. Telophase II Write down one thing that is occurring in this phase. The result: 4 Nonidentical (genetically different) haploid cells.

Karyotyping Directions: Read Page 1. Analyze the three Karyotypes. Answer the six questions on the back of your section Assessment (Page 278, 1-5) Sometimes mistakes occur during Meiosis especially during Metaphase I and Metaphase II. During these two phases chromosomes must line up in the middle of the plate, spindle fibers must attach to the appropriate chromosomes and finally pull them in the correct direction. If this does happen, genetic disorders can occur. In this activity, you will analyze a Karyotype and determine the consequences when mistakes are made during Meiosis. Answers: 47, XX, +21 4. Down Syndrome 47, XXY 5. Klinefelter’s 47, XY, +13 6. Trisomy 13

Summary Prompt Why is it so important that no mistakes occur during Meiosis? Give an example. Sentence Starter: It is important that no mistakes occur during Meiosis because ___________. An example is ___________. Did you meet today’s objective? Circle 1 2 3 If there is extra time, random call: 2-3 students to share what they wrote.