1. Cell Replication: Cell Cycle
Chapter 10

2. * Cells must divide for the following reasons:
So that an organism can grow
So that an organism can develop
Repair

3. Bacteria cells undergo binary fission to divide
Bacteria cells undergo binary fission to divide. This is a form of asexual reproduction, where the parent passes exact copies of the DNA to its offspring (Remember- Bacterial cells are prokaryotes!)

4. Eukaryotic Cells must form chromosomes before cell division.
Nucleus (DNA is found here)
Chromosome Structure
DNA is found on chromosomes inside the nucleus.

5. One Gene. Most chromosomes have several hundred genes.
Centromere- Where the 2 chromatids are attached.
One Chromosome
Chromotids – Where genes are located.

6. Before cell division can take place, each chromosome must copy itself:
This chromosome now has sister chromatids. They are identical in genetic material to each other.

7. One chromosome that has copied its DNA.

9. G1 
Rapid Cell Growth;
Occupies most of the cell’s life.
S DNA is copied.
G2 Microtubules are assembled
Mitosis  Nucleus divides
Cytokinesis Cytoplasm divides

10. Mitosis and Cytokinesis produce new cells that are identical to the original cell. Allows cells to grow and replace damaged tissues. 46 46 46

11. The Cell Cycle is Controlled!
Proteins act as signals that can permit or delay the next phase of the cell cycle.
Checkpoints in the Cell Cycle:
1. G1  If the cell is healthy, then its DNA will copy.
2. G2  DNA replication is checked. If it occurred correctly, then mitosis is triggered.
3. Mitosis  Signals beginning of G1.

12. Cancer
Occurs when a cell loses control of the cell cycle. The cell barrels thru the checkpoints.

13. VI. Mitosis  Division of the Nucleus

14. Interphase
This is the time when the genetic material is actually being used to govern or regulate cell activity. Chromosomes are not visible during Interphase.

15. Prophase Chromosomes become visible. (Chromosome is already copies).
Nuclear envelope dissolves.

16. Metaphase
Chromosomes line up along equator.

17. Anaphase Centromeres divide.
Chromatids (now called chromosomes) move toward opposite poles.

18. 2 genetically identical daughter cells.
Telophase
Nuclear envelope forms at each pole.
Chromosomes uncoil.
Spindle dissolves.
Cytokinesis begins.
2 genetically identical daughter cells.

20. Review
I. Mitosis  DNA Replication & Division = 2 daughter cells genetically identical to the parent cell. Video of Mitosis 46 2n 46 46 2n 2n
Body Cell

21. II. Meiosis  Reduction Division; Four daughter cells genetically different from the parent cell.
Parent Reproductive Cell
23 n
23 n
23 n
23 n
23 n
23 n

22. Phases of Meiosis  A round of DNA replication occurs before stage I.

23. Stage I Meiosis I : Prophase I
Begin with a diploid cell.
Each chromosome seeks out its corresponding homologous chromosome to form a tetrad.
Each Tetrad contains 4 chromatids.

24. While together, homologous chromosomes exchange genetic information during a process called crossing over.
Ex. A A B B C C D D E E F F

25. Stage II Meiosis I : Metaphase I
Homologous chromosomes (tetrads) line up across the center of the cell.

26. Stage III Meiosis I : Anaphase I
Spindles pull the tetrads apart.

27. Stage IV Meiosis I : Telophase I & Cytokinesis
At the end of telophase, cytokinesis occurs.
2 new daughter cells that are haploid and genetically different from the parent cell have formed.

28. Review of Meiosis I

29. Meiosis Practice

30. Stage V Meiosis II : Prophase II
A new spindle forms around the chromosomes.

31. Stage VI Meiosis II : Metaphase II
Chromosomes line up at the equator.

32. Stage VII Meiosis II : Anaphase II
Centromeres divide.
Sister chromatids split (now called chromosomes) and move to opposite ends of each cell.

33. Stage VIII Meiosis II : Telophase II
A nuclear envelope forms around each set of chromosomes.
The result: 4 haploid daughter cells that are genetically different form the parent cell.

34. Review of Meiosis II

35. Meiosis II Practice

36. Meiosis In Males vs. Females
Oogenesis
Spermatogenesis

37. Genetic Variation
3 events give rise to genetic variation in sexually reproducing individuals.
Crossing Over  Homologous chromosomes exchange genes.
Independent Assortment  which cell each homologous chromosome will end up in is random.
Random Fertilization  The random mating of organisms in nature.

38. Genetic Variation Speeds Up Evolution!!
It offers new combinations of traits that the environment can choose for or against.