9.5 Meiosis in Sexual Reproduction

Gametes = 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” Gametes = Haploid Sex Cells (sperm/egg)

Already duplicated in preparation for division 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

Humans _____Chromosomes, ______Pairs One from Mom One from Dad 2 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

Two divisions 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

Metaphase I - tetrads line-up along the equator of the spindle 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.

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.

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