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AIM: What events take place at each phase of meiosis? DO NOW: What is the difference between gametes and body (somatic) cells? Define Homologous Chromosomes.

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Presentation on theme: "AIM: What events take place at each phase of meiosis? DO NOW: What is the difference between gametes and body (somatic) cells? Define Homologous Chromosomes."— Presentation transcript:

1 AIM: What events take place at each phase of meiosis? DO NOW: What is the difference between gametes and body (somatic) cells? Define Homologous Chromosomes VOCABULARY: meiosis, diploid, haploid, gamete, tetrad, homologous chromosomes, crossing over New updated syllabus! Hand in New York Times Article Summary HW due next Tuesday read chapter Answer questions pg 278 #1-5 Quiz on Meiosis Wednesday 2/24 HAVE A GREAT VACATION!

2 Review of Do Now What is the difference between gametes and body (somatic) cells? Define Homologous Chromosomes

3 Overview of Meiosis Diploid Vs. Haploid 2 cell divisions –4 haploid daughter cells Reduction of chromosome number 2n  n Homologous chromosomes Contributes to genetic diversity –New combinations of chromosomes –Crossing over during prophase I

4 AIM: What events take place at each phase of meiosis? Do Now: What are homologous chromosomes? What is the goal of meiosis? What is crossing over? VOCABULARY: meiosis, diploid, haploid, gamete, tetrad, homologous chromosomes, crossing over HW due tomorrow Read Chapter Answer questions pg Wednesday Quiz on Meiosis (Chapter 11-4) HW due Friday Pg 1025, ques 1-19 and 22

5 The Phases of Meiosis Meiosis I Prophase I* Metaphase I* Anaphase I* Telophase I * indicates significant differences from mitosis Meiosis II Prophase II Metaphase II Anaphase II Telophase II Events in all phases of meiosis II are very similar to mitosis. IN YOUR NOTEBOOKS: Outline events and sketch cells in each phase of meiosis I and II. Chart Three columns—Name of phase, events, sketch.

6 Crossing Over

7 Meiosis I Interphase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Metaphase I Spindle fibers attach to the chromosomes. Anaphase I The fibers pull the homologous chromosomes toward the opposite ends of the cell.

8 Meiosis II Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Anaphase II The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells.

9 Questions How could the final products of meiosis be different than the ones shown in the diagram? Are these the only possible products of meiosis for the cell in the diagram? Explain. In your groups: Where does this different arrangement originate (which phase of meiosis)?

10 AIM: What events take place at each phase of meiosis? Do Now: How could a cell have 46 chromosomes and be haploid? VOCABULARY: meiosis, diploid, haploid, gamete, tetrad, homologous chromosomes, crossing over Have out HW Quiz tomorrow on Meiosis (Chapter 11-4) HW due Friday Pg 1025, ques 1-19 and 22

11 Review of HW Describe the main result of meiosis –Four haploid cells genetically different from each other and from the original cell What do the terms diploid and haploid mean? –Diploid: two sets of chromosomes; haploid is one set of chromosomes What is crossing over? –Homologous chromosomes pair up and form tetrads, which may exchange portions of their chromatids, resulting in the exchange of alleles between the homologous chromosomes In human cells 2N=46. How many chromosomes would you expect to find in a sperm cell? In an egg cell? In a white blood cell? Explain. –Both sperm and egg cells have 23 chromosomes because they are gametes, which are haploid cells. A white blood cell has 46 chromosomes because it is a diploid body cell.

12 Compare and Contrast Mitosis vs. Meiosis Function Location in Body Number of Daughter Cells Change in Chromosome Number Number of Phases Number of Cell Divisons Difference in DNA between parent cell and daughter cells

13 Review of Meiosis How many phases are there? What is a tetrad and when does it form? When does crossing over take place? What happens in metaphase I, anaphase I and telophase I? What happens in metaphase II, anaphase II and telophase II? Which stage of meiosis is most like mitosis? What do you think would happen if the homologous pairs didn’t fully separate during anaphase I?

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