1. Mitosis & Meiosis

2. Chromosome Structure  Chromatin – Thin, uncoiled strands of DNA & proteins (histones)  Chromosomes – Rod-shaped structures composed of coiled strands of DNA & proteins.  Chromosomes are made up of two sister chromatids held together at a central point called a centromere.

3. Chromosomes

4. Chromosome Numbers  Chromosomes appear in pairs in all sexually reproducing organisms. ◦ Called homologous chromosomes ◦ Same shape & same size  Diploid number (2N) – A cell containing both chromosomes of a homologous pair.  Haploid number (1N) – A cell containing one chromosome of a homologous pair.

5. Diploid vs. Haploid Cells

6. Mitosis  SOMATIC CELL REPRODUCTION ◦ Somatic cells are body cells ◦ Germ cells are reproductive/sex cells (gametes) ◦ Mitosis creates two daughter cells that are exact replicas of the original cell ◦ Size causes a cell to divide

7. The Cell Cycle  G1 Period – Cell growth  S Period – DNA Replication  G2 Period – Rapid cell growth  Mitosis – Cell division  Cytokinesis – Cytoplasmic division

8. The Cell Cycle

9. Interphase  Comprised of the G1, S, & G2 periods.  A period of preparation for mitosis.

10. The Phases of Mitosis  Period of nuclear division ◦ Prophase ◦ Metaphase ◦ Anaphase ◦ Telophase

11. Prophase  Chromatin coils to form chromosomes.  Nucleolus & nuclear membrane disappear.  Spindle fibers begin to develop. ◦ Kinetochore fibers (pole to chromosomes); ◦ Polar fibers (pole to pole)  Formation of asters.  Asters: Protein fibers that radiate from each pole.

12. Metaphase  Chromosomes move to the equator/center of the cell.  Metaphase plate formation

13. Anaphase  Centromeres of each pair of chromatids divide.  Chromatids separate & move to opposite poles.

14. Telophase  Centrioles & spindle fibers disappear  Chromatids unwind to form chromatin  Nuclear membrane & nucleolus reappear

15. Cytokinesis  The division of the cytoplasm  ANIMAL CELL – cleavage furrow  PLANT CELL – cell plate formation Cell Plate

16. Phases of Mitosis

17.  Process of nuclear division that reduces chromosome number in half.  Used to create germ cells (gametes)  Two divisions ◦ Meiosis I ◦ Meiosis II

18.  Prophase I ◦ Nuclear membrane/nucleolus disappear ◦ Chromosomes form from chromatin ◦ Homologous chromosomes line up together (tetrads) ◦ Crossing over occurs (Genetic Recombination) ◦ Spindle fibers form.  Metaphase I ◦ Homologous chromosomes move to equator.  Anaphase I ◦ Homologous chromosomes separate & move to poles.  Telophase I ◦ Cytoplasm divides (forms 2 daughter cells) ◦ Nuclear membrane & nucleolus reappear Crossing Over

19.  Most like Mitosis  Prophase II ◦ Nuclear Membrane & nucleolus disappear  Metaphase II ◦ Chromosomes line up on equator  Anaphase II ◦ Chromatids separate  Telophase II ◦ Nuclear membrane & nucleolus reappear ◦ Chromosomes uncoil

21.  Spermatogenesis ◦ Occurs in males. ◦ Four sperm cells are formed.  Oogenesis ◦ Occurs in females. ◦ I egg (ovum) formed. ◦ 3 polar bodies formed, but eventually disintegrate.

22.  Not all cells move through the cell cycle at the same rate. ◦ Nerve cells don’t divide at all once developed & cells of skin grow & divide rapidly.  Controls on cell growth can be turned on & off.  Cyclins: Proteins that regulate the cell cycle in eukaryotic cells.  Cancer: Cells fail to respond to signals that regulate the cell growth.