I. Forms of DNAA. When the cell is NOT

dividing = chromatinB. When the cell IS dividing

= chromosome

Bivalentchromosome

Monovalentchromosome

II. Why do cells divide?A. Replacement - cells wear

out & dieB. Repair - tissues can be

damaged by injury or infection

C. Growth of the organismD. Reproduction

III. Types of cell divisionA. Mitosis

1. New cells are identical to the old cells

2. Chromosome number is the same in parent & daughter cells (diploid -2n)

3. Growth, repair, & asexual reproduction

MITOSIS

B.Meiosis1. Parent cell divides twice

to produce 4 cells2. Produces gametes (sex

cells –sperm/eggs)3. Daughter cells have half

the original number of chromosomes (haploid -1n)

4.When two gametes join to form a zygote, it will have the normal # of chromosomes

MEIOSIS

5. Daughter cells are not Genetically identical a.) Homologous

chromosomes separate, sending one version of each to the new cells.

b.) Crossing –Over: sometimes chromosomal segements are exchanged between Homologous Chromosomes.

IV. Phases of MitosisA. Interphase

1. Growth & normal cell activities

2. DNA = chromatin

*as the cell prepares for division, DNA is duplicated

B. Prophase1. Chromatin thickens

& reveals duplicated chromosomes (bivalent)

2. Centrioles move to poles

3. Nuclear membrane dissolves

C.Metaphase1. Bivalent

chromosomes line up along equator of cell

2. Chromosomes attach to spindle fibers

D.Anaphase1. Spindle fibers pull monovalent chromosomes to opposite ends of cell

**an identical set of chromosomes moves to each pole

E.Telophase1. Chromosomes

uncoil & become chromatin again – Nuc. Memb Reforms

2. Cytokinesis: cell membrane pinches in to form 2 separate cells

V. Phases of MeiosisI. Cells go through two

rounds of division during meiosis, resulting in 4 haploid cells

http://www.youtube.com/watch?v=eaf4j19_3Zg&safe=active

http://www.pbs.org/wgbh/nova/body/how-cells-divide.html

Meiosis I & IISection 11-4

Sam

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Diff

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