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Cell Division
Cell division – parent cell divides into 2
daughter cells
2 types of cell division:
1) mitosis – division of somatic (body) cell
to produce identical somatic cells
-occurs in a series of phases
Interphase
• part of cell cycle when cell is not dividing
• DNA replication occurs during this time as
well as all other cell activities
*includes G1, S, and G2
Prophase
• first phase of mitosis
• chromatid pairs shorten, thicken, become
visible
• centrioles move to opposite poles
• spindle fibers form (between centrioles)
• nuclear membrane, nucleolus disappear
*Plant cells have no centrioles, but spindle
still forms
Metaphase
• chromatid pairs line up along middle of
spindle (equator)
• spindle fibers attach to centromere of each
chromatid pair
Anaphase
• chromatid pairs move to opposite poles of
the spindle
• separation of chromatid pairs signals the
start of anaphase
Telophase
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final phase of mitosis
begins when chromosomes arrive at poles
chromosomes get longer, thinner
spindle breaks down
nuclear membrane forms around each set
of chromosomes, nucleolus reappears
• cell begins to divide in two
Telophase
• cytokinesis – division of cytoplasm
Plant cell vs. Animal cell cytokinesis:
Plant –
Animal cell plate forms,
membrane pinches
elongates, forming
inward & forms a
new cell wall
depression or cell
furrow
2) Meiosis – division of germ cells (diploid
somatic cells) to produce
monoploid/haploid cells (gametes)
Diploid – (2n) – two copies of each
chromosome
Haploid/monoploid – (1n) – one copy of
each chromosome
Meiosis
• Interphase – DNA replication
• Prophase I – homologous chromosomes
pair up & form 4-stranded groups called
tetrads
-chromosomes enlarge, exchange
corresponding segments of DNA (crossing
over)
Meiosis
• chromosomes shorten, thicken, become
visible
• spindle forms, nuclear membrane &
nucleolus break down
Metaphase I – tetrads move toward middle
of spindle & line up along equator
-spindle fibers attach to centromeres
Meiosis
Anaphase I – chromatid pairs forming each
tetrad move to opposite poles
Telophase I – nuclear membrane reappears
-cytoplasm begins to divide & form either
cell plate or cell furrow
(This first division is the reduction division)
Meiotic Interphase – NO DNA replication
Meiosis
Prophase II - chromatid pairs shorten/thicken
-no tetrads (since they already separated in
the first division)
-spindle begins to form; nuclear membrane
breaks down
Meiosis
Metaphase II – paired chromatids line up at the
equator; spindle fibers attach to centromeres
of each chromatid
Anaphase II – members of each chromatid pair
move apart to opposite poles
Telophase II – nuclear membrane reappears;
cytokinesis occurs; chromosomes become
long, thin
Meiosis
• 4 haploid cells result
(gametogenesis)
Spermatogenesis – formation of sperm
-4 evenly sized cells
Oogenesis – formation of egg cells
-1 egg & 3 small polar bodies