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CELL DIVISION mitosis & meiosis. Forms of DNA When the cell is NOT dividing = chromatin When the cell IS dividing = chromosome. Monovalent chromosome. Bivalent chromosome. Why do cells divide? Replacement - cells wear out & die Repair - tissues can be damaged by injury or infection - PowerPoint PPT Presentation
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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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