9.5 Meiosis in Sexual Reproduction

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

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 divisionHumans _____Chromosomes, ______Pairs One from Mom One from Dad2 Gametes (n) join during fertilization forming a 2n cell called a Zygote.

Mitosis starts with 1 2n cell ends with 2 2n cells genetically identical

Meiosis starts with 1 2n cell ends with 4 n cells genetically mixed

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

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

Telophase 1 & Cytokinesis occurs

NO INTERPHASE AKA NO DNA REPLCIATIONPMAT STARTS ALL OVER AGAINProphase II Metaphase II Anaphase II Telophase IIOccur similar to mitosis.

Possible gamete combinations = 2n where n is the number of chromosomes

So humans its 223Or 8,400,000 possible gamete combinations!