AP Biology Meiosis Part 2

Mom and Dad’s DNA contribution The egg surrounded by sperm.

TWO Divisions

Interphase

(First Division)

(Second Division)

Spermatogenesis Epididymis Seminiferous tubule Testis Cross section of seminiferous tubule Spermatogonium Mitotic division, producing large numbers of spermatogonia Sertoli cell nucleus Differentiation and onset of meiosis I Primary spermatocyte (in prophase of meiosis I) Meiosis I completed Secondary spermatocyte Meiosis II Lumen of Seminiferous tubule Early spermatids Spermatids (at two stages of differentiation) Differentiation Sperm cells Neck Head Midpiece Tail Plasma membrane Acrosome Nucleus Mitochondria

Oogenesis in the ovaries Ovary Primary germ cell in embryo Differentiation Oogonium in ovary Oogonium Mitotic division Primary oocyte within follicle Primary oocyte Completion of meiosis I and onset of meiosis II Growing follicle Secondary oocyte First polar body Ovulation Entry of sperm triggers completion of meiosis II Mature follicle Ruptured follicle Second polar body Ovum Ovulated secondary oocyte Corpus luteum Degen- erating corpus luteum

Crossover in Prophase I

Mitosis vs. Meiosis

(before chromosome replication) MITOSIS MEIOSIS Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Propase Prophase I Chromosome replication Chromosome replication Tetrad formed by synapsis of homologous chromosomes Duplicated chromosome (two sister chromatids) 2n = 6 Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase Metaphase I Anaphase Sister chromatids separate during anaphase Homologues separate during anaphase I; sister chromatids remain together Anaphase I Telophase Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II Sister chromatids separate during anaphase II

Independent Assortment Key Maternal set of chromosomes Possibility 1 Possibility 2 Paternal set of chromosomes Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4