Meiosis Essay

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Meiosis 10.1.1 Describe the behaviour of the chromosomes in the phases of meiosis. Two divisions occure during meiosis, these are termed meiosis I and meiosis II. Each division involves the four stages of prophase, metaphase, anaphase and telophase. Meiosis I Prophase I • Chromosomes coil up tightly and become visible under a light microscope • Homologous chromosomes pair up and crossing over occures (the point of cross over is known as the chiasma) • Nuclear membrane disintgrates and the centrioles travel to the poles of the cell Metaphase I • Microtubules form a spindle and the spindle fibers attach to the centromeres of the chromosomes • Pairs of homologous chromosomes align along the equator Anaphase I • Spindle fibers shorten pulling paired homologous chromosomes in opposite directions • Paired homologous chromosomes are seperated and pulled to opposite poles so that each pole contains one chromosome of each pair. Telophase I • A nuclear membrane forms around the chromosomes at each pole and chromosomes uncoil • The cell undergoes cytokinesis to form two daughter cells • Forms two haploid cells • At the end of telophase I the cells may enter a short interphase period or proceed directly to meiosis II • DNA is not replicated Meiosis II Prophase II • Chromosomes coil up again • Centrioles move to the cell poles • Nuclear membrane disintergrates Metaphase II • Spindle fibers attach to the the centromeres • Chromosomes align along the equator Anaphase II • Spindle fibers shorten • Centromeres split • Chromatids of each chromosome travel to opposite poles Telophase II • Nuclear membrane forms around the chromatids at each pole, once the membrane is formed, each chromatid is then called a chromosome. • Both cells undergo cytokinesis to form four cells • Chromosomes uncoil • Nucleoli form 10.1.2 Outline the formation of

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