1. Why do cells divide?

2. The Cell Cycle

3. Why do cells divide? Repair Growth Reproduction  Some organisms reproduce by cell division (asexual) Limit on size

4. Chromosomes Genetic material is composed of DNA Most of the time, DNA is in the form of chromatin (unraveled; in use)

5. Chromosomes Before the cell divides, chromatin is replicated and condensed to form chromosomes (humans have 46) Each chromosome consists of 2 identical copies called sister chromatids joined by a centromere

6. The Cell Cycle The cell cycle consists of 2 phases:  Interphase G1, S, G2  Mitotic Phase Mitosis (4 stages) Cytokinesis

7. Interphase Time in between cell divisions Interphase is broken into 3 sub-phases:  G1 – cell works and grows  S – DNA (chromatin) duplicates  G2 – cell prepares to divide

8. Mitotic Phase Mitosis – Division of nucleus  Prophase  Metaphase  Anaphase  Telophase Cytokinesis – Division of cytoplasm

9. The Mitotic Spindle Microtubules that separate the sister chromatids Grows from centrosomes

11.  Chromosomes are separated into sister chromatids  Chromosomes form  Spindle fibers attach to the chromatids  Chromosomes line up in the middle of the cell  Spindle elongates the cell by pushing the poles apart  Genetic material exists as chromatin  Chromatids are separated and move towards the poles  Spindle disappears  2 nuclei reappear  The cytoplasm splits, forming 2 cells  Nuclear envelope breaks down  Cell is growing & working; genetic material replicates

12. Mitosis Prophase  Chromosomes form  Nucleus breaks down  Centrosomes move to poles  Spindle fibers attach to the chromosomes

13. Mitosis Metaphase  Chromosomes line up in the middle of the cell

14. Mitosis Anaphase  Chromosomes are separated into sister chromatids  Spindle elongates the cell

15. Mitosis Telophase  Chromatids reach the poles  Spindle disappears  2 nuclei reappear  Cleavage furrow appears

16. Cytokinesis  The cytoplasm splits, forming 2 cells

17. Summary The cell cycle begins with one cell The cell undergoes a series of steps: Interphase – Prophase – Metaphase – Anaphase – Telophase – Cytokinesis 2 identical daughter cells have been produced

18. Restriction Point

19. Cell Cycle Checkpoints Restriction point (G1)  Internal surveillance  External surveillance Density dependence Anchorage dependence

20. Cancer Benign tumor Malignant tumor  Metastasis Treatment  Surgery  Radiation therapy  Chemotherapy

21. Meiosis

22. Diploid vs haploid Cells with two sets of chromosomes are called diploid (2n) Cells with one set of chromosomes are called haploid (n)

23. Homologous chromosomes You inherit one chromosome of each type from each parent Homologous chromosomes are the 2 matching chromosomes  44 autosomes  2 sex chromosomes

25. Meiosis The process by which 4 haploid gametes are produced, each with half the number of chromosomes as the diploid parent  Sperm – male gamete  Egg – female gamete If a human body cell has 46 chromosomes, how many does a human gamete have?

26. Meiosis Meiosis involves 2 divisions  Meiosis I – splits homologous pairs  Meiosis II splits sister chromatids

27. Major Events Prophase I  Crossing over Anaphase I  Homologous pairs separate Anaphase II  Sister chromatids separate

28. Meiosis promotes genetic diversity Produces 4 genetically different daughter cells During prophase 1, homologous chromosomes can exchange pieces of genetic material to form totally new chromosomes (crossing over)

29. Errors in Meiosis A nondisjunction occurs when chromosomes or chromatids fail to split

30. Activity: Mitosis vs Meiosis Fill in the chart to compare the two types of cell division. Fill in the chart