Meiosis

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)

Prophase 1 Similar as mitosis, except… Two Events: 1) Synapsis: Pairing of homologous chromosomes The four chromatids equal a TETRAD 2) Crossing Over: Exchange of genes

Early Prophase

Synapsis: Homologous chromosomes align

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

Cytokinesis divides the cells Telophase 1 Cytokinesis divides the cells Each cell contains 1 of the homologous chromosomes (23 total)

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 Cytokinesis divides the cells Chromatids uncoil End Result: Four haploid cells

Defined: Production of sperm cells Occurs in male testes Spermato- genesis Defined: Production of sperm cells Occurs in male testes Meiosis produces four haploid sperm cells at a time

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

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