CELL DIVISION

BIOLOGY 106

OUTLINE

- Types of cell division

- Mitosis

oPhases of mitosis

oDiagram shows how mitosis works

- Meiosis

oPhases of meiosis

oDiagram shows how meiosis works

MITOSIS

- This type of cell division allows multicellular organism to grow and repair damage tissue.

- Mitosis produce two daughter cells that are identical to the parent cell.

MITOSIS SUBDIVIDED INTO 5 PHASES

Interphase: takes about 90% of the cell cycle

-The cell can grow and copy its chromosomes.

o1- Prophase

o2-Prometaphase

o3-Metaphase

o4-Anaphase

o5-Telophase

Cytokinasis

o1- Prophase

-Chromosome condensed and become shorter

-Nucleoli disappear

-The centrosomes duplicate and mitotic spindle fibers begin to form.

o2-Prometaphase

-The nuclear envelope fragmented.

-The chromosomes become shorter and attached to spindle fibers.

o3-Metaphase

-The centrosomes are at the opposite poles of the cell.

-The chromosomes arranged on the metaphase plate.

o4-Anaphase

-Tow sister chromatids are separated.

-Chromatids moving toward the opposite poles

o5-Telophase

-Tow daughter nuclei are formed

-Nuclear envelope arises

-Chromosomes become less condensed.

-Spindle fibers disappear

Cytokinesis:

Cytoplasm begins to divide in order to give tow daughter cells that have the same number of chromosomes and genetically identical to the mother cells.

MITOSIS

MEIOSIS

• Enable the organisms to reproduce sexually.

• Occurs only in the gonad (Ovary & testis)

• Gives rise to male and female gametes.

• Involves tow nuclear division producing 4 daughter cells.

MEIOSISMeiosis I

(Reduction division)

1- Prophase I

2- metaphase I

3- Anaphase I

4- Telophase I

Cytokinesis

Meiosis II

(Mitotic division)

- See mitotic division

MEIOSIS I(REDUCTION DIVISION)

1- Prophase I

A)Chromosomes condensed & become shorter.

B)Disappearance of nucleolus & nuclear envelope

C)Formation of spindle fibers

D)Homologues pairs of chrmosomes are united together

E)Crossing over occures….

2- metaphase I

-Pair of homologues chromosomes arrange at equator (Metaphase plate)

-Chromosomes attach to the spindle fibers.

3- Anaphase I

- Separation of homologues pairs of chrmosomes.

4- Telophase I

-Nucleolus & nuclear membranes reappear.

-Spindle fiber disappear.

Cytokinesis :

-Occurs by dividing the cell into tow daughter cells.

-The producing cells have half chromosomal of mother cells and differ genetically from them

MITOSIS VS MEIOSIS