1. Today: - Lab 4 Debrief - Mitosis - Lunch - Meiosis
Other: Blood Drive Today!
TIME: 11:00am 1:00pm + 2:00pm 5:00pm 
PLACE: Baxter Events Center

2. Thinking About Mitosis
When and where do you want your cells to divide?

3. The Role of Mitosis 1. Growth & Development 2. Repair
3. Asexual Reproduction

4. A Few Terms:
A single CHROMOSOME duplicates to form a pair of SISTER CHROMATIDS, with a visible CENTROMERE.

5. Remembering How Chromosomes are Formed…

6. Homologous Chromosomes
DIPLOID organisms have two of each chromosome. These pairs are called HOMOLOGOUS Chromosomes.

7. The Mitotic Cell Cycle: An Overview
~90% of the cell cycle

8. The Mitotic Cell Cycle: An Overview

9. Cell Cycle Checkpoints
Three parts:
1. A signal specific to a particular event (like DNA replication)
2. A signal transduction pathway
3. A target to receive the signal, typically linked to key enzymes needed for the next step
What happens to a cell if its checkpoints don’t work correctly??

10. Cyclin-Dependent Kinases Help Regulate the Cell Cycle

11. External Factors Also Regulate Cell Division

12. What do you notice about these two cultures?
Do either of them demonstrate density-dependent inhibition?

13. The Mitotic Cell Cycle: Focus on Mitosis

14. Mitosis Occurs in 4-5 Steps:
Prophase  Prometaphase Metaphase  Anaphase  Telophase

15. Step 1: Prophase Chromatin condenses to form ‘visible’ chromosomes
Microtubules are reassembled, spindle begins to form
Centrosomes migrate away from one another

16. Step 2: Prometaphase Nuclear envelope fragments
Microtubules extend from each pole towards the middle of the cell
Spindle microtubules attach to the kinetochores and begin to move the chromosomes
(Nature: , 2000 )

17. Step 3: Metaphase Spindle is complete
“Push-pull” aligns chromosomes at the midpoint to form the METAPHASE PLATE

18. Step 4: Anaphase
Sister Chromatids separate (released at centromere) and migrate towards opposite spindle poles
Spindle elongates

19. Step 5: Telophase Chromosomes arrive at poles and relax
Nuclear membrane reforms
Spindle is disassembled

21. Let’s watch: http://www.cellsalive.com/mitosis.htm

22. Thinking About How Chromatids Move
Attachment of the microtubules to the kinetochores creates the “tug of war” that generates the metaphase plate.
During Anaphase, the proteins holding the sister chromatids together are inactivated, allowing the chromosomes to separate and move toward opposite poles.

23. Testing the Hypothesis:

24. Finally! CYTOKINESIS!

25. You Try! House Rules: Homologous Chromosomes should be the same length
Sister Chromatids should be the same color and length

26. Asexual Reproduction occurs through MITOSIS
and
CYTOKINESIS
The resulting offspring are CLONES (genetically identical to the parent)!

27. Mitosis Allows for Asexual Reproduction, but Not Sexual Reproduction!

28. Asexual vs Sexual Reproduction
Advantages and Disadvantages?

29. Genes: discrete units of coded information (DNA)
Inheriting Genes:
Genes: discrete units of coded information (DNA)
Genes are packaged on CHROMOSOMES. A gene’s location along the length of a chromosome is its LOCUS

30. Sexual Reproduction  Genetic Variation!
Through sexual reproduction, offspring inherit new combinations of alleles.
An ALLELE is a “version” of a particular gene
Genetic Diversity is Essential for Evolution!

31. Sexual Reproduction requires MEIOSIS- (reduces the chromosome number to half)
In humans, each SOMATIC CELL, has 23 pairs of HOMOLOGOUS CHROMOSOMES, or a total of 46 CHROMOSOMES.

32. Important Exception! One pair of Chromosomes are NOT Necessarily Homologous…
SEX CHROMOSOMES: Human females have a homologous pair of X chromosomes (XX) in their somatic cells; males have one X and one Y chromosome (XY)

33. Our GAMETES (reproductive cells) are HAPLOID.
Humans do have HAPLOID cells, or cells containing a single set of the 22 autosomes plus a single sex chromosomes. (n=23)
Our GAMETES (reproductive cells) are HAPLOID.

34. The Human Life Cycle
Note that Meiosis and Fertilization are opposing processes.
Meiosis reduces the chromosome number to half (n=23)
Fertilization restores the chromosome number (2n=46)

36. Meiosis is the Process that Produces Haploid Gametes
Meiosis is similar to Mitosis:
Cells copy their DNA in S-Phase
Cells divide in a series of steps, ProphaseMetaphaseAnaphaseTelophase
Unlike Mitosis, in Meiosis, cells divide twice, creating four, haploid daughter cells

37. Meiosis occurs in two stages:
Meiosis I- Homologous chromosomes separate
Meiosis II- Sister chromatids separate

38. Overview of Meiosis I:
Pairs of duplicated, homologous chromosomes (tetrads) align at the metaphase plate.
Crossover occurs between Homologous Chromosomes
Duplicated Homologous Chromosomes are separated in Anaphase
The Cytoplasm Divides, producing two haploid cells

39. Overview of Meiosis II:
Sister chromatids in the haploid cells line up at the metaphase plate and are separated.
The cell divides into 2 haploid daughter cells.
Thus Meiosis of a single, diploid cell produces 4 haploid daughter cells.

42. Comparing Mitosis and Meiosis

43. MEIOSIS I in real cells:

44. MEIOSIS II in real cells:
Let’s Watch!

45. You Try! House Rules: Homologous Chromosomes should be the same length
Sister Chromatids should be the same color and length

46. Challenge Question
Compare the amount and arrangement of genetic material in each cell following telophase I of meiosis and telophase of mitosis.