1. Cell Division

2. DAY I

3. Cell Division: Mitosis & Meiosis
The process by which two cells are formed from one.
There are two types of cell division: mitosis and meiosis.
Most of the time when people refer to cell division, they mean mitosis, the process of making new body cells.
Meiosis is the type of cell division that creates egg and sperm cells.

4. Mitosis Let’s consider mitosis first:
Mitosis is a fundamental process for life.
A cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Each of which begins the cycle again.

5. Cell Division - Mitosis
There are 4 phases of mitosis:
Prophase
Metaphase
Anaphase
Telophase

6. Prophase
Centrioles
Spindles forming
The first phase and longest of mitosis; occurs when chromatin condenses becoming chromosomes and the mitotic spindle begins to form.
Spindles; fanlike microtuble structures which help to separate chromosomes.
The centrioles separate to opposite sides of the nucleus organizing spindles
Chromosomes (Paired identical “sister” chromatids)
The nuclear envelope begins to break down (dashed line)

7. Metaphase Centrioles Chromosomes line up along the equator
Typically happens very quickly
Chromosomes line up along the equator.
(Note: This is a signature feature of metaphase.)
Each chromosome is connected along the poles of the spindle fiber at its centromere

8. Anaphase The “sister” chromatids separate into individual chromosomes
and move apart to opposite poles
(Note: These are signature features of anaphase.)
Phase ends when chromosomes stop moving

9. Telophase Fourth and final phase (not stage) of mitosis
Nuclear Envelope Reforming
Fourth and final phase (not stage) of mitosis
Chromosomes begin to disperse into a tangle of dense material.
Nuclear membrane (envelope) forms around each group of chromosomes
The spindle begins to break apart, and a nucleolus becomes visible in each daughter nucleus.
Cytokinesis begins
virtual.yosemite.cc.ca.us

10. Meiosis Background
Each organism must inherit a single copy of every gene from each of the parents.
Two sets of genes must be separated from each other so that each gamete contains just one set of genes.
Show McGraw-Hill Clip:

11. Class Activity Read section comparing mitosis and meiosis on Pg. 278
Using a Venn diagram and begin comparing and contrasting the two forms of cell division.

12. Comparing Mitosis and Meiosis
Mitosis results in the production of two genetically identical diploid (2N) cells
Meiosis produces four genetically different haploid cells.
Mitosis allows an organism’s body to grow and replace cells.
Asexual reproduction occurs when a new organism is produced by mitosis of the cell or cells of the parent organism.
Meiosis begins with a diploid cell but produces four haploid (N) cells.
Haploid cells are genetically different from the diploid cells.
Meiosis is how sexually reproductive organisms produce gametes.

13. DAY II

14. If both chromosomes of a pair are present, the cell is diploid
Diploid Cells
Chromosomes in early interphase (actually chromatin)
Chromosomes after replication (ready for mitosis or meiosis)
If both chromosomes of a pair are present, the cell is diploid
Homologous Pairs

15. Diploid Cells cont. All body cells are diploid.
Sex cells: egg and sperm are haploid cells
Spores are also haploid cells

16. 46 36 # of Chromosomes 23 23 18 18 HUMAN CAT
Total Chromosomes in a diploid cell
# of homologous pairs in a diploid cell
Total chromosomes in haploid cell (gamete)
HUMAN 46
CAT 36 23 23 18 18

17. Meiosis
How are haploid (N) gamete cells produced from diploid (2N) cells?
MEIOSIS - The process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
Involves two divisions, called Meiosis I and Meiosis II
By the end of Meiosis II, the diploid cell that entered meiosis has become 4 haploid cells

18. Sex Cells Gametes or Germ Cells
Also know as Sex Cells
Only contain one copy of genetic information
Have one chromosome of each pair or half that of diploid cells.
When only ONE chromosome of a pair is present, the cell is HAPLOID

19. Why is Haploid Important?
If diploid cells are fertilized… +
2N N  N
Chromosome number will keep doubling!!

20. Why is Haploid Important?
If haploid cells are fertilized… +
N N  N
The Result is a Diploid Cell!
Like all cells of the body!!

21. Sexual Reproduction
Reproductive process in which haploid sex cells (gametes) fuse to produce a diploid fertilized egg (zygote) +
EGG SPERM Fertilized Egg
(ZYGOTE)
GAMETES

22. Chromosome Number Ex: Adult Fruit Fly
A body cell contains 8 chromosomes.
4 chromosomes (male parent); 4 (female parent).
Both sets are considered homologous.
Each of the chromosomes from male parent correspond with one of the female parent.
A cell containing both set of homologous chromosomes is said to be diploid (2N).
Contain two complete sets of chromosomes and two complete sets of genes.
The diploid number is 8 (2N = 8).
The gametes (sexually reproducing) of fruit flies contain a single set of chromosomes (single set of genes) are set to be haploid (N).

23. MEIOSIS Cell division that reduces the number of chromosomes in half
Occurs in sex cells (germ cells: Egg and Sperm)
Two Divisions
MEIOSIS I
MEIOSIS II
Meiosis I
Meiosis II

24. MEIOSIS I Prior to meiosis I, each chromosome is replicated.
Similar to mitosis.
**Remember in mitosis, the 4 chromosomes line up individually in the center of the cell and then the two chromatids of each chromosome separate.

25. Meiosis I: Prophase I Chromosomes condense & become distinctly visible
Nuclear membrane and nucleolus disappear
Synapsis – homologous chromosomes pair up forming a tetrad (4 chromatids).
Crossing Over – exchange of DNA creating genetic variability

26. Meiosis I: Metaphase I Homologous chromosomes line up at the equator
PAIRS of chromosomes rather than INDIVIDUAL chromosomes line up!

27. Meiosis I: Anaphase I / Telophase I
Homologous chromosomes separate and move to opposite poles
Cells are still diploid
TELOPHASE I:
Cell membrane pinches in forming 2 HAPLOID cells.

28. MEIOSIS II
The two cells produced by meiosis I now enter a second meiotic division.
No replication.

29. MEIOSIS II: Prophase II
Cells are haploid.
Cells get ready to divide again.

30. MEIOSIS II: Metaphase II
Chromosomes align at the equator

31. MEIOSIS II: Anaphase II / Telophase II
Sister chromatids move to opposite poles
TELOPHASE II:
Cell membrane
pinches in
Nuclear membrane
reappears.

32. Interphase????
There is NO
interphase
between
Meiosis I and
Meiosis II

33. Resulting Sex Cells
Four HAPLOID sex cells are produced.

34. MEIOSIS

35. Mitosis: http://www.biologycorner.com/bio1/cellcycle.html
Mitosis vs. Meiosis:
How Cells Divide?:
Meiosis and Mitosis: