1. Cell division
Mitosis & Meiosis

2. Cell Review Cells have DNA, the information needed for life.
DNA is packaged into something called chromosomes.

3. Cell division
All complex organisms originated from a single fertilized egg.
Through cell division the numbers are increased
Cell then specialise and change into their various roles (blood cell, bone cell, nerve cell, etc)

4. Why do cells divide?
Growth
Reproduction
Replacement of dying cells – skin, blood cells

5. Chromosomes replicate
Cell division in prokaryotes: Binary fission
Bacteria have a single chromosome (versus the 46 humans have).
Chromosomes replicate
Cell membrane pushes inward
Cell divides in two,
each with a chromosome

7. Types of cell division in Eukaryotes
Mitosis:
Growth, development & repair
Asexual reproduction (yields identical cells)
Occurs in somatic (body) cells
Produces 2 identical cells
Meiosis:
Sexual reproduction (yields different cells)
Occurs in reproductive cells (gametes)
Produces 4 DIFFERENT cells
So far, I’ve been talking about mitosis only
What? Somatic (body) cells
Why? Growth & development, repair lost or injured cells
Allows many organisms to reproduce asexually
But there is a 2nd type of cell division - meiosis that occurs only in select cells within certain tissue at particular phases of an organism’s lifetime.
meiosis is involved with organisms that undergo SEXUAL REPRODUCTION
--means of reducing number of chromosomes in sperm or egg so when combined through fertilization, the original number is restored
-- reduction of genetic state from diploidy to haploidy necessary
--occurs in reproductive organs in humans -- ovary & testis -- produces haploid cells called gametes (sperm, egg)
--completed with fertilization of male gamete & female gamete to produce diploid zygote

8. A comparison of mitosis and meiosis

9. Paper Plate Models
Each group will be in charge of making a paper plate model of mitosis.
Each person will find mitosis in the book and model each stage on a paper plate with yarn.
Yarn will represent the chromosomes.
Then the cell stages will be strung together to make a cell mobile.

10. Example Write the name of the phase in back of the plate Interphase
Prophase
Metaphase
Anaphase
Telophase

11. Mitosis
All daughter cells contain the same genetic information from the original parent cell from which it was copied.
Every different type cell in your body contains the same genes, but only some act to make the cells specialise into nerve or muscle tissue.

12. Mitosis overview Parent cell
Chromosomes are copied and double in number
Chromosomes now split
2 daughter cells identical to original

13. Mitosis

14. First step Interphase begins first. Chromosomes are copied
Chromosomes appear as thread (chromatin)

17. Centrioles appear and begin to move to opposite ends of cell.
Prophase
Mitosis begins
Chromatin (DNA thread) condenses, causing the chromosomes to begin to become visible (X’s).
Centrioles appear and begin to move to opposite ends of cell.
Spindle fibers, made of microtubules, form between the poles
- Nucleolus disappears

20. 2. Metaphase
- Chromosomes align on an axis called the metaphase plate
- Chromatids (or pairs of chromosomes) attach to the spindle fibers

22. - Cell begins to elongate
3. Anaphase
- Chromatids (or pairs of chromosomes) separate at the centromere (center) and begin to move to opposite ends of the cell
- Cell begins to elongate

24. 4. Telophase Formation of nuclear membrane and nucleolus
Two new nuclei form
Chromosomes appear as chromatin (threads rather
than rods)
Mitosis ends.
Formation of the cleavage furrow - a shallow groove in the cell near the old metaphase plate

26. Cytokinesis Division of the cytoplasm
AT THE END the daughter cells have the SAME number of chromosomes as the PARENT/MOTHER cell.

28. Mitosis Flip Book
You will complete each page to illustrate the changes that take place in a cell during cell division.
The first oval (or ovals) in EACH phase should show the location of the organelles at that stage.
Use the extra ovals to show the movement of organelles between stages.
Write a brief description of each stage on the blank side of your page.
Interphase
Interphase is the
stage where….

29. Mitosis Animated
animation

30. Mitosis

33. Mitosis in an onion root
Can you identify some of the stages of Mitosis here?

34. Anaphase
Interphase
Telophase
Metaphase
Prophase

35. Type of cell division that halves number of chromosomes
Meiosis
Type of cell division that halves number of chromosomes
1N is one chromosome
2N is two chromosome (sister chromatids)
2 divisions involved
Product is gamete, essential for sexual reproduction 2N 1N

36. Terms
Homologous Chromosome: a chromosome that has the same DNA (ex: 2 of the same chromosomes that hold the DNA for hair color and eye color.)
Crossing over: when the chromosome from the male and from the female swap DNA.

37. Overview of meiosis: how meiosis reduces chromosome number
In Metaphase I, Homologous chromosomes
line up next to each other
In Prophase I, Homologous chromosomes
cross over and swap DNA.
This allows diversity in offspring.
First part of meiosis
involves separating
homologous chromosomes
Second part
involves separating
chromatids
Homologous
Same chromosome

38. Overview of meiosis: how meiosis reduces chromosome number
In Anaphase I, Homologous chromosomes
Are pulled apart.
In Telophase I, Homologous chromosomes
are in separate cells.
First part of meiosis
involves separating
homologous chromosomes
Second part
involves separating
chromatids
homologous

39. Overview of meiosis: how meiosis reduces chromosome number
In Prophase II, there is no
REPLICATION or Crossing over.
In Anaphase II, chromatid (2N) separates,
moving one chromosome (1N) per cell.
First part of meiosis
involves separating
homologous chromosomes
In metaphase II,
Chromosomes line up in the 2 cells.
In Telophase II, each of the 4 daughter cells
should have one copy of each chromosome.
Cells are NOT identical due to crossing over
and swapping DNA.
Second part
involves separating
chromatids

40. The results of crossing over during meiosis
Crossing over helps to promote genetic variation.
Two homologous chromosomes can code for the same traits, but the variety in the traits may be different.
Example: single gene controls the color of flower petals, but there may be several different versions of the gene.

41. Evolutionary advantage
asexual reproduction (mitosis)
easy, rapid, effective way to reproduce
useful in stable environment
lack of genetic diversity among offspring
sexual reproduction (meiosis)
promotes genetic variability
useful in changing environment
Asexual reproduction - CLONING
1. Formation of new individuals by mitotic cell divisions
2. Easy, rapid, and effective way to reproduce
3. Useful in stable environment
4. Lack of genetic diversity among offspring (genetically identical, clones) -- which are disadvantage in changing environments
Sexual reproduction
a.Results in unique combinations within sets, promoting genetic diversity
b. Diversity promotes evolutionary opportunity through novel genetic combinations
c.Result of fertilization, fusion of gametes