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

4. Same process –G1: Growth, normal functions, and organelles created –S: Chromatin duplicated –G2: Growth and normal functions

5. Synthesis (S stage) Chromatin strands duplicated

6. 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 Mom 1 Dad 1

7. Early Prophase Dad #2 Mom #2 Mom #1 Dad #1 Dad #3 Mom #3 Chromosomes form Nucleus dissolves

8. Synapsis Dad #2 Mom #2 Mom #1 Dad #1 Dad #3 Mom #3 Spindle fibers pull homologous chromosomes together tetrad

9. Homologous chromosomes (tetrads) align along cell equator Dad #2 Dad #3 Dad #1 Mom #2 Mom #3 Mom #1

10. Tetrads separated Homologous chromosomes are pulled to opposite ends Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

11. Cytokinesis begins to divide the cells’ cytoplasm Each cell contains 1 of the homologous chromosomes –Humans: 23 full chromosomes each Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

12. No Interphase 2 The Point of Meiosis: –Reduce the amount of chromosomes by half If Interphase 2 were to happen… –DNA would be duplicated AGAIN during the S stage Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3 Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

13. Cytokinesis divides the cells Each cell contains 1 of the homologous chromosomes –Humans: 23 full chromosomes each Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

14. Same as mitosis Note: No new DNA was created (no 2 nd interphase) Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

15. Remaining chromosomes are aligned at cell equator Mom #2 Dad #2 Mom #1 Dad #3 Dad #1 Mom #3

16. Sister chromatids are pulled to opposite ends

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

19. Defined: Production of sperm cells Location: male testes Makes final changes to sperm cell Four haploid sperm cells at a time Meiosis 1 Meiosis 2 Spermatogenesis spermatogonium

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

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

22. Review 1) Name three ways that meiosis and mitosis differ. 2) Pick a stage of meiosis…any stage. Describe what happens in it. 3) What type of cells does meiosis create? 4) What are homologous chromosomes? 5) When do homologous chromosomes move to opposite ends of the cell? 6) When do chromatids move to opposite ends of the cell? 7) Why is no DNA created in meiosis 2? 8) How does meiosis differ in males vs. females?

23. 1)Name three ways that meiosis and mitosis differ. 2) Pick a stage of meiosis…any stage. Describe what happens in it. Answers will vary 3) What type of cells does meiosis create? Gametes (egg, sperm, pollen) and they are haploid 4) What are homologous chromosomes? Chromosomes that contain the same genes. Example: Chromosome #11 from your mom and chromosome #11 from your dad are homologous chromosomes. Mitosis Division of somatic cells End Result: 2 Diploid Cells Importance: Replaces aging cells & a form of asexual reproduction Meiosis Division of gametes End Result: 4 Haploid Cells Importance: Reduces the gamete chromosome number by half

24. 5) When do homologous chromosomes move to opposite ends of the cell? Anaphase I 6) When do chromatids move to opposite ends of the cell? Anaphase II 7) Why is no DNA created in meiosis 2? The cell only goes through interphase (S stage) once – before Meiosis I. Plus the cell is trying to reduce the chromosome number. 8) How does meiosis differ in males vs. females? Males = spermatogenesis = 4 sperm Females = Oogenesis = 1 ovum and 3 polar bodies