Meiosis

Quick review: identify this stage of the diploid cell cycle. Prophase

Quick review: identify this stage of the diploid cell cycle. telophase

Quick review: identify this stage of the diploid cell cycle. anaphase

Quick review: identify this stage of the diploid cell cycle. metaphase

Quick review: identify this stage of the diploid cell cycle. interphase

Meiosis Meiosis Defined: Process where the chromosome number is reduced by half Gametes created (egg & sperm) End Result: Four Haploid Cells

Interphase Same process (G1, S, G2) Chromatin duplicated

Synthesis (S stage) Chromatin strands duplicated

Prophase 1 Similar as mitosis, except… Two Events: 1) Synapsis: Pairing of homologous chromosomes Dad’s #1 chromosome pairs with Mom’s #1, etc… The four paired chromatids equals a TETRAD 2) Crossing Over: Exchange of genes

Early Prophase Chromosomes form Nucleus dissolves

Synapsis tetrad tetrad Spindle fibers pull homologous chromosomes together tetrad

Homologous chromosomes (tetrads) align along cell equator Metaphase 1 Homologous chromosomes (tetrads) align along cell equator

Homologous chromosomes are pulled apart to opposite ends Anaphase 1 Homologous chromosomes are pulled apart to opposite ends Tetrads separated

Each cell contains 1 of the homologous chromosomes Telophase 1 Each cell contains 1 of the homologous chromosomes In humans = 23 chromosomes Cytokinesis divides the cells

Note: No new DNA was created (no 2nd interphase) Prophase 2 Same as mitosis Note: No new DNA was created (no 2nd interphase)

Remaining chromosomes are aligned at cell equator Metaphase 2 Remaining chromosomes are aligned at cell equator

Sister chromatids are pulled to opposite ends Anaphase 2 Sister chromatids are pulled to opposite ends

Telophase 2 Nucleus reforms on the four new cells Chromatids uncoil Cytokinesis divides the cells End Result: Four haploid cells

Defined: Production of sperm cells Spermatogenesis Meiosis 1 Defined: Production of sperm cells Occurs in male testes Meiosis produces four haploid sperm cells at a time Meiosis 2 Spermatogenesis

Oogenesis Defined: Production of the egg cell (ovum) oocyte Oogenesis Meiosis 1 Defined: Production of the egg cell (ovum) During meiosis I: Cytoplasm distributed unequally After meiosis II: 1 cell matures 3 “Polar Bodies” dissolve Meiosis 2 Oogenesis

Mitosis Meiosis Division resulting in gametes Ex: Sperm and Egg cells End Result: 4 Haploid cells (n) Importance: Reduces the gamete chromosome number by half Division of somatic cells Ex: Blood cells, skin cells, nerve cells… End Result: 2 Diploid Cells (2n) Importance: Replaces aging cells Importance: Form of asexual reproduction