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Meiosis Chapter 10, Section 2
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Diploid & Haploid Cells
Diploid = a cell with two sets of chromosomes, 2n, somatic (body) cells muscle, skin, liver, etc. Haploid = a cell with one set of chromosomes, gametes, 1n, sperm and eggs Meiosis forms haploid gametes required for sexual reproduction Meiosis has 2 stages Meiosis I Meiosis II
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Interphase and stages of mitosis
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Chromosomes from metaphase stage of mitosis
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Below are chromosomes after they split into chromatids during (telophase) of mitosis
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Separation of homologous pairs
MEIOSIS I Separation of homologous pairs Homologous Pair = in a diploid cell the 2 sets of chromosomes pair up
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1. Prophase I DNA coils into chromosomes
Nuclear envelope & nucleolus break down Synapsis = homologous chromosomes pair up into tetrads Crossing-over = homologous pairs switch pieces of their chromatids Genetic Recombination = maternal & paternal genetic info get shuffled during crossing-over
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2. Metaphase I Tetrads line up in the middle of the cell
Spindle fibers attach at the centromeres of each homologous chromosome
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3. Anaphase I Each homologous chromosome moves to the opposite end of the cell Independent Assortment = random separation of chromosomes, allows for genetic variation
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4. Telophase I & Cytokinesis I
Two newly formed cells are haploid Each chromosome is still made up of two chromatids
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Separation of sister chromatids
MEIOSIS II Separation of sister chromatids Sister Chromatids = identical halves of a chromosome that has been duplicated
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5. Prophase II 2 newly created cells from Meiosis I start to divide
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6. Metaphase II Chromosomes line up in the center
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7. Anaphase II Sister Chromatids separate
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8. Telophase II & Cytokinesis II
4 new cells, each with half the number of chromosomes of the original cell
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Development of Gametes
Spermatogenesis = production of sperm cells Oogenesis = production of mature egg cells
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Nondisjunction Nondisjunction = failure of homologous pairs to separate in Meiosis I If an organism survives, it may have a genetic disorder
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Polyploidy Polyploid = organisms with more than the usual number of chromosome sets Occurs frequently in plants, results in plants that are larger than normal
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