I. Forms of DNA
A. When the cell is NOT
dividing = chromatin
B. When the cell IS dividing =
chromosome
Monovalent
chromosome
Bivalent
chromosome
II. Why do cells divide?
A. Replacement - cells wear out
& die
B. Repair - tissues can be
damaged by injury or infection
C. Growth of the organism
D. Reproduction
III.Types of cell division
A. 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.Meiosis
1.Parent cell divides twice to
produce 4 cells
2.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 Mitosis
A. Interphase
1. Growth & normal
cell activities
2. DNA = chromatin
*as the cell prepares
for division, DNA
is duplicated
B.Prophase
1. Chromatin thickens &
reveals duplicated
chromosomes
(bivalent)
2. Centrioles move to
poles
3. Nuclear membrane
dissolves
C.Metaphase
1.Bivalent
chromosomes line
up along equator
of cell
2.Chromosomes
attach to spindle
fibers
D.Anaphase
1.Spindle fibers pull
monovalent
chromosomes to
opposite ends of cell
**an identical set of
chromosomes moves
to each pole
E.Telophase
1.Chromosomes uncoil
& become chromatin
again – Nuc. Memb Reforms
2.Cytokinesis: cell
membrane pinches
in to form 2 separate
cells
V. Phases of Meiosis
I. Cells go through two rounds
of division during meiosis,
resulting in 4 haploid cells
http://www.pbs.org/wgbh/nova/b
ody/how-cells-divide.html
http://www.youtube.com/watch?v=eaf4j19_3Zg&safe=active
Meiosis I & II
Section 11-4