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Meiosis Group 3- Student 1, Student 2, Student 3, Student 4, Student 5, Student 6 What is meiosis? Meiosis occurs in order to form gametes during sexual reproduction in eukaryotes. Meiosis results in four genetically different, haploid daughter cells from one diploid cell. While mitosis is completed by most types of cells within an organism, meiosis is only completed by the gonads, or reproductive organs within the organism. Phases of Meiosis: After DNA has replicated in the S phase of the cell life cycle, Meiosis is completed in a series of phases similar to mitosis, but meiosis has two divisions instead of one: Meiosis I Prophase I Metaphase I Anaphase I Telophase I & Cytokinesis Meiosis II Prophase II Metaphase II Anaphase II Telophase II & Cytokinesis Meiosis I: Prophase I During Prophase I, DNA condenses into chromosomes and becomes visible, crossing over occurs, and the nuclear envelop disappears, centrioles start to move toward the poles and the meiotic spindle appears. Crossing Over https://www.youtube.com/watch?t=27& v=5x_Rp1mwotQ Prophase I is important because this is where crossing over occurs Crossing Over results in the genetic variation of the four daughter cells During crossing over, parts of homologous chromosomes may break off and pair with another set of chromosomes Meiosis I: Metaphase I During metaphase I, the sister chromosomes line up along the center of the cell and spindle fibers that extend from the centrioles attach to the centromere region of the chromosomes. Meiosis I: Anaphase I The spindle fibers begin to shorten and the cell elongates as microfilaments push against each other. Chromosomes move towards each pole of the cell. Meiosis I: Telophase I & Cytokinesis During telophase I, the homologous chromosome pairs are at either end of the cell and cytokinesis occurs. Cytokinesis is the process where a cleavage furrow forms, pinching the cell into two daughter cells that are not identical to the parent cell or to each other due to crossing over that occurred. The two daughter cells only remain in this stage for a short period before beginning Meiosis II. Meiosis II: Prophase II Both of the two daughter cells from Meiosis I enter Meiosis II starting with Prophase II. The sister chromatids condense and the meiotic spindle appears. Crossing over does not occur during prophase II. Centrioles move towards the poles of the cell. Meiosis II: Metaphase II The sister chromatids line up along the center of the cell and the spindle fibers attach to the centromere region of the chromosomes. Meiosis II: Anaphase II Spindle fibers shorten, separating sister chromatids and moving chromosomes to opposite poles of the cell. The cell elongates due to microfilaments pushing against each other. Meiosis II: Telophase II and Cytokinesis During telophase II, the sister chromatids are at opposite ends of the cell. The nuclear envelops form around the chromatids at each end of the cell and the cleavage furrow begins to form. During cytokinesis, the cleavage furrow pinches the new cells in two. The End Result: The completion of meiosis results in four haploid daughter cells that are all genetically different due to genetic recombination that occurs during crossing over in prophase I. References http://www2.estrellamountain.edu/faculty/farabe e/BIOBK/BioBookmeiosis.html http://www.aboutkidshealth.ca/en/howthebodyw orks/geneticsintroduction/celldivision/meiosisintr oduction/pages/stagesofmeiosisi.aspx All images were retrieved from Microsoft Clipart Online Gallery from Bing.com