Presentation on theme: "AIM: What events take place at each phase of meiosis?"— 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 ChromosomesVOCABULARY: meiosis, diploid, haploid, gamete, tetrad, homologous chromosomes, crossing overNew updated syllabus!Hand in New York Times Article SummaryHW due next Tuesday read chapter Answer questions pg 278 #1-5Quiz on Meiosis Wednesday 2/24HAVE A GREAT VACATION!
2 Review of Do NowWhat 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 cellsReduction of chromosome number 2nnHomologous chromosomesContributes to genetic diversityNew combinations of chromosomesCrossing 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 overHW due tomorrow Read Chapter Answer questions pgWednesday 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 mitosisMeiosis IIProphase IIMetaphase IIAnaphase IITelophase IIEvents 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.
7 Spindle fibers attach to the chromosomes. Meiosis IAnaphase IProphase IInterphase IMetaphase IThe fibers pull the homologous chromosomes toward the opposite ends of the cell.Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.Cells undergo a round of DNA replication, forming duplicate Chromosomes.Spindle fibers attach to the chromosomes.
8 Meiosis II results in four haploid (N) daughter cells. Prophase IIMetaphase IIAnaphase IIMeiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.The chromosomes line up in a similar way to the metaphase stage of mitosis.Telophase IIThe sister chromatids separate and move toward opposite ends of the cell.Meiosis II results in four haploid (N) daughter cells.
9 QuestionsHow 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 overHave out HWQuiz 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 cellWhat do the terms diploid and haploid mean?Diploid: two sets of chromosomes; haploid is one set of chromosomesWhat 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 chromosomesIn 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 FunctionLocation in BodyNumber of Daughter CellsChange in Chromosome NumberNumber of PhasesNumber of Cell DivisonsDifference 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?