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9.5 Meiosis in Sexual Reproduction

9.5 Meiosis in Sexual Reproduction. Haploid cells have only one set of chromosomes, abbreviated as “n” . Diploid cells are those with two ( di ) sets = “2n”. Gametes = Haploid Sex Cells (sperm/egg).

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9.5 Meiosis in Sexual Reproduction

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  1. 9.5 Meiosis in Sexual Reproduction

  2. Haploidcells have only one set of chromosomes, abbreviated as “n” Diploid cellsare those with two (di) sets = “2n” Gametes = Haploid Sex Cells (sperm/egg)

  3. Homologous chromosomes: A pair of chromosomes in which one member of the pair is obtained from the organism's maternal parent and the other from the paternal parent; found in diploid cells. Already duplicated in preparation for division

  4. Humans _____Chromosomes, ______Pairs One from Mom One from Dad 2 Gametes (n) join during fertilization forming a 2n cell called a Zygote.

  5. Mitosis starts with 12n cell ends with 22n cells genetically identical Meiosis starts with 12n cell ends with 4n cells genetically mixed

  6. Twodivisions occur, Meiosis I (Reduction) and Meiosis II (Division) Prophase I Unique Event!!! Homologues group forming tetrads - Crossing over occurs - chromatids break and may be reattached to a different homologous chromosome

  7. Metaphase I - tetrads line-up along the equator of the spindle. Spindle fibers attach to the centromere region of each homologous chromosome pair Anaphase I - tetrads separate, and are drawn to opposite poles by the spindle fibers. The centromeres in Anaphase I remain intact.

  8. Telophase 1 & Cytokinesis occurs NO INTERPHASE AKA NO DNA REPLCIATION PMAT STARTS ALL OVER AGAIN Prophase II  Metaphase II  Anaphase II  Telophase II Occur similar to mitosis.

  9. Possible gamete combinations = 2n where n is the number of chromosomes So humans its 223 Or 8,400,000 possible gamete combinations!

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