1. Mitosis & Meiosis

2. Mitosis occurs in all the somatic (body) cells Why does mitosis occur?
Mitosis – division of the nucleus into 2 nuclei, each with the same number of chromosomes
Mitosis occurs in all the somatic (body) cells
Why does mitosis occur?
So each new daughter cell has nucleus with a complete set of chromosomes

3. 4 phases of nuclear division (mitosis), directed by the cell’s DNA (PMAT)
Prophase
Metaphase—(Middle)
Anaphase—(Apart)
Anaphase—(Apart)
Telophase—(Two)

4. Prophase Chromosomes coil up Nuclear envelope disappears
Spindle fibers form

5. Metaphase—(Middle) Chromosomes line up in middle of cell
Spindle fibers connect to chromosomes

6. Anaphase—(Apart) Chromosome copies divide
Spindle fibers pull chromosomes to opposite poles

7. Telophase—(Two) Chromosomes uncoil Nuclear envelopes form
2 new nuclei are formed
Spindle fibers disappear

8. Cytokinesis — the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides
In animal cells the cytoplasm
pinches in
In plant cells a cell plate forms
After mitosis and cytokinesis, the cell returns to Interphase to continue to grow and perform regular cell activities

10. Summary: Cell Cycle
Interphase Mitosis (PMAT) Cytokinesis
When cells become old or damaged, they die and are replaced with new cells

11. Cell Division Control
DNA controls all cell activities including cell division
Some cells lose their ability to control their rate of cell division – the DNA of these cells has become damaged or changed (mutated)
These super-dividing cells form masses called tumors

12. Mitosis:
If a cell wants to make a duplicate of itself, it first must copy its DNA (part of a chromosome).
The copies then must be separated & sorted into two sides of the cell.
The cell then splits in two. Part of each parent is carried to the two new cells.
Results in cells such as internal organs, skin, bones, blood, etc.

13. Amoeba SIsters Mitosis

14. Meiosis:
As in mitosis, if a cell wants to make a duplicate of itself, it first must copy its DNA (part of a chromosome).
Results in reproductive cells (sperm, eggs, etc).
Part of each parent is carried to the four new cells.
Meiosis has evolved to solve a problem.
The problem is this: some organisms have sex with other organisms – that is, they combine their genes together (creating genetic diversity).
Why would this be a problem?

15. Amoeba Sisters Meiosis

16. This may you remember these terms:
MITosis takes the cell and Makes It Two (diploid)
Meiosis has to do with sex
From the cell’s point of view:
mITosis results in Identical Twins
mEioSis results in Egg and Sperm (haploid)
Clyde Freeman Herreid – Dept. of Biological Sciences: Buffalo State Univ. of New York

17. Each resulting cell still has chromosomes from mom & dad
Mitosis: Meiosis:
Explain the randomness in meiosis
End of first class
Each resulting cell still has chromosomes from mom & dad

18. Meiosis Meiosis animation:
Beginning of third class

19. Vocabulary Diploid Haploid Germ cell Somatic cell Interphase Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

21. Meiosis Interphase
Meiosis is preceded by interphase. The chromosomes have not yet condensed.

22. Meiosis Interphase
The chromosomes have replicated, and the chromatin begins to condense.

23. Meiosis Prophase I
The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one another

24. Meiosis Metaphase I
The nuclear membrane dissolves and the homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles.

25. Meiosis Anaphase I The chromosomes move to opposite ends of the cell.

26. Meiosis Telophase I & Cytokinesis
The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes.

27. Meiosis Prophase II The cell has divided into two daughter cells.

28. Meiosis Metaphase II
As in Meiosis I, the chromosomes line up on the spindle fibers.

29. Meiosis Anaphase II
The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell.

30. Telophase II & Cytokinesis
With the formation of four cells, meiosis is over. Each of these prospective germ cells carries half the number of chromosomes of somatic cells.