05. Cell Division

7/28/2019 05. Cell Division

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CellDivision



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Cell Division

All cells are derived from pre-existing cells

New cells are produced for

growth and to replace damaged orold cells

Differs in prokaryotes (bacteria)

and eukaryotes (protists, fungi,plants, & animals)



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Types of Cells

Somatic Cells• All body cells except sex cells• Contain diploid (2n) number of chromosomes•

Undergo mitosis

Sex Cells• The gametes, the sperm cell of the male

and the egg cell of the female• Contain haploid number (n) of chromosomes• Undergo mitosis and meiosis



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Keeping Cells Identical

The instructions formaking cell parts

are encoded in theDNA, so each newcell must get a

complete set of theDNA molecules



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DNA ReplicationDNA must be

copied or replicatedbefore celldivision

Each new cell

will then have an identical copy ofthe DNA

Original DNAstrand

Two new,

identical DNA

strands



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Identical Daughter Cells

Parent Cell

Two identical

daughter

cells



Chromosomes



Prokaryotic Chromosome

The DNA ofprokaryotes(bacteria) is one,

circularchromosome attached to the

inside of the cellmembrane



Eukaryotic ChromosomesAll eukaryotic cells store genetic

information in chromosomes Most eukaryotes have between 10 and50 chromosomes in their body cells

Human body cells have 46 chromosomesor 23 identical pairs



Eukaryotic ChromosomesEach chromosome is composed of a

single, tightly coiled DNA moleculeChromosomes can’t be seen whencells aren’t dividing and are calledchromatin



Compacting DNA intoChromosomes

DNA istightly

coiledaround proteins

calledhistones



AP Biology

double-strandedmitotic human

chromosomes



Chromosomes in Dividing Cells

Duplicatedchromosomes arecalled sister

chromatids &are heldtogether by thecentromere

Called Sister Chromatids



AP Biology

Mitotic Chromosome

Duplicated chromosome 2 sister chromatids

narrow at centromeres

contain identical

copies of original DNAhomologous

chromosomes homologous

chromosomes

sister chromatids homologous = “same information”

single-strandeddouble-stranded



KaryotypeA picture of thechromosomes froma human cellarranged in pairs by

sizeFirst 22 pairs arecalled autosomes

Last pair are thesex chromosomes

XX female or XY male

B Gi l?



Boy or Girl?

Y - Chromosome

X - Chromosome

The Y Chromosome Decides



Cell Reproduction



Types of Cell ReproductionAsexual reproduction involves a

single cell dividing to make 2 new,identical daughter cells

Mitosis & binary fission are

examples of asexual reproductionSexual reproduction involves twocells (egg & sperm) joining to make a

new cell (zygote) that is NOT identical to the original cellsMeiosis is an example



Cell Division inProkaryotes



Cell Division in Prokaryotes Prokaryotes such as

bacteria divide into 2identical cells by theprocess of binaryfission

Single chromosomemakes a copy ofitself

Cell wall formsbetween thechromosomes dividingthe cell

Parentcell

2 identical daughter cells

Chromosomedoubles

Cell splits



Prokaryotic CellUndergoing Binary Fission

f B F



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Animation of Binary Fission



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The CellCycle

C ll C l



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Cell Cycle

•The cyclical process ofgrowth and mitosis

Fi Ph f h C ll C l



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Five Phases of the Cell Cycle

G1 - primary growth phaseS – synthesis; DNA replicatedG2 - secondary growth phase

collectively these 3 stages are called interphase

M - mitosisC - cytokinesis



AP Biology

Cell Cycle

M

Mitosis

G1

Gap 1

G0

Resting

G2

Gap 2

S

Synthesis

Cell has a “life cycle”

cell is formed from

a mitotic division

cell grows & matures

to divide again

cell grows & matures

to never divide again

G1, S, G2, M G1G0

epithelial cells,

blood cells,

stem cells

liver cells

brain / nerve cells

muscle cells



AP Biology

Interphase

90% of cell life cycle cell doing its “everyday job”

produce RNA, synthesize proteins/enzymes

prepares for duplication if triggered

I’m working here!

Time to divide& multiply!

C ll C l



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Cell Cycle

I t h



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Interphase

Preparatory stage for mitosisCell is not resting

The nucleus is clearly visiblewith one or more distinct nucleoli

Chromosomes appear as

irregular-granular form, thuscannot be recognized



AP Biology

Interphase

Divided into 3 phases: G1 = 1st Gap (Growth)

cell doing its “everyday job”

cell grows

S = DNA Synthesis copies chromosomes

G2 = 2nd Gap (Growth)

prepares for division

cell grows (more) produces organelles,

proteins, membranes

G0

green = key features



AP Biology

Interphase

Nucleus well-definedDNA loosely packed in

long chromatin fibers

Prepares for mitosis replicates

chromosome

DNA & proteins

produces proteins &organelles


I t h G St



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Interphase - G1 Stage

Pre-Synthesis Interphase

1st growth stage after cell

divisionCells mature by making morecytoplasm & organelles

Cell carries on its normalmetabolic activities

I t h S St



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Interphase – S StageSynthesis stage

DNA is copied or replicated

Twoidenticalcopiesof DNA

Original

DNA



AP Biology

Synthesis phase of Interphase dividing cell replicates DNA

must separate DNA copies

correctly to 2 daughter cells human cell duplicates ~3 meters DNA

each daughter cell gets complete

identical copy

error rate = ~1 per 100 million bases 3 billion base pairs in mammalian

genome

~30 errors per cell cycle

mutations (to somatic (body) cells)

S phase: Copying / Replicating DNA



AP Biology

Organizing DNA

DNA is organized inchromosomes double helix DNA molecule

wrapped around histone

proteins like thread on spools

DNA-protein complex =chromatin

organized into long thin fiber condensed further during

mitosis

DNA

histones

chromatin

duplicated mitotic chromosome

ACTGGTCAGGCAATGTC

double stranded chromosome



AP Biology

Copying DNA & packaging it…

After DNA duplication, chromatin condenses coiling & folding to make a smaller package

DNA

chromatin

mitotic chromosome

Int ph G St



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Interphase – G2 Stage

2nd

Growth StageOccurs after DNA has been copied

All cell structures needed for

division are made (e.g. centrioles)Both organelles & proteins are

synthesized



AP Biology

double-strandedmitotic human

chromosomes



AP Biology

Mitotic Chromosome

Duplicated chromosome 2 sister chromatids

narrow at centromeres

contain identical

copies of original DNAhomologous

chromosomes homologous

chromosomes

sister chromatids homologous = “same information” single-stranded double-stranded

Wh t’ H pp nin in Int ph



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What s Happening in Interphase

What the cell looks like

Animal Cell

What’s occurring



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Mitosis

Mitosis



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MitosisDivision of the

nucleusAlso calledkaryokinesis

Only occurs ineukaryotes

Has four stages

Doesn’t occur insome cells suchas brain cells

Four Mitotic Stages



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Four Mitotic Stages

Prophase

Metaphase

Anaphase

Telophase




AP Biology

Prophase

Chromatin condenses visible chromosomes

chromatids

Centrioles move to oppositepoles of cell

animal cell

Protein fibers cross cell to formmitotic spindle

microtubules

actin, myosin coordinates movement of

chromosomes

Nucleolus disappears

Nuclear membrane breaks down

g y

Early Prophase



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Early ProphaseChromatin in nucleus condenses to

form visible chromosomesMitotic spindle forms from fibers incytoskeleton or centrioles (animal)

Chromosomes

Nucleolus Cytoplasm

Nuclear Membrane

Late Prophase



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Late ProphaseNuclear membrane & nucleolus are

broken downChromosomes continue condensing &are clearly visible

Spindle fibers called kinetochores attach to the centromere of each

chromosomeSpindle finishes forming between thepoles of the cell

Late Prophase



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Late Prophase

Nucleus & Nucleolus have disintegrated

Chromosomes

Spindle Fiber attached to



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Spindle Fiber attached toChromosome

Kinetochore Fiber

Chromosome

Review of Prophase



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Review of Prophase


What’s happening

Spindle Fibers



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Spindle FibersThe mitotic spindle form from the

microtubules in plants and centriolesin animal cellsPolar fibers extend from one pole of

the cell to the opposite poleKinetochore fibers extend from thepole to the centromere of the

chromosome to which they attachAsters are short fibers radiatingfrom centrioles

Sketch The Spindle



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Sketch The Spindle

Metaphase



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MetaphaseChromosomes, attached to the

kinetochore fibers, move to the centerof the cell

Chromosomes are now lined up at the

equator

Pole of

the Cell

Equator of Cell

Metaphase



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Metaphase

Chromosomeslined at theEquator

Asters atthe poles

SpindleFibers

Metaphase



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Metaphase

Aster

Chromosomes at Equator

Review of Metaphase



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Review of Metaphase


What’s

occurring

Anaphase



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Anaphase

Occurs rapidly

Sisterchromatids are

pulled apart toopposite poles of the cell by

kinetochorefibers



AP Biology

Separation of chromatids

In anaphase, proteins holding together sister chromatids are inactivated

separate to become individual chromosomes

2 chromosomes1 chromosome

2 chromatids

single-strandeddouble-stranded

Anaphase



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Anaphase

Sister

Chromatidsbeingseparated



AP Biology

Kinetochores usemotor proteins that

“walk” chromosome

along attached

microtubule

microtubule

shortens by

dismantling atkinetochore

(chromosome) end

Chromosome movement

Anaphase Review



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Anaphase Review

What thecell looks

like

What’soccurring




AP Biology

Telophase

Chromosomes arrive atopposite poles

daughter nuclei form

nuclear envelope formsaround each set of sister chromatids

nucleoli form

chromosomes disperse no longer visible under

light microscope

Spindle fibers disperse

Comparison of Anaphase & Telophase



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Comparison of Anaphase & Telophase



AP Biology

Mitosis in animal cells



AP Biology

Mitosis in plant cell

Cytokinesis



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CytokinesisMeans division of the cytoplasm

Division of cell into two,identical halves called daughtercellsIn plant cells, cell plate formsat the equator to divide cell

In animal cells, cleavage furrowforms to split cell



AP Biology

Cytokinesis in Animals

(play Cells Alive movies here)

(play Thinkwell movies here)

Cytokinesis

http://localhost/Users/kfoglia/Kim's%20NEW%20WORK/Division%20Ave%20-%20Levittown/AP%20Bio/MOVIES/Ch12%20The%20Cell%20Cycle/mitosis-CellsAlive.swf








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Cytokinesis

Cleavage furrowin animal cell Cell plate inanimal cell



AP Biology

Cytokinesis in Plants

Plants cell plate forms

vesicles line up at

equator

derived from Golgi

vesicles fuse to form

2 cell membranes

new cell wall laid

down betweenmembranes

new cell wall fuses

with existing cell wall

Mitotic Stages



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Mitotic Stages

Daughter Cells of Mitosis



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Daughter Cells of MitosisHave the same number of

chromosomes as each other and asthe parent cell from which theywere formed

Identical to each other, but smallerthan parent cell

Must grow in size to become maturecells (G1 of Interphase)




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Chromosome number the same, but cellssmaller than parent cell

What isthe 2n

ordiploidnumber?

2



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Review

ofMitosis

Draw & Learn these Stages



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Name the Mitotic Stages:



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Interphase

Prophase

Metaphase

Anaphase

Telophase

Name the Mitotic Stages

Name this?

Name this?

Eukaryotic Cell Division



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y

Used for growth andrepair

Produce two new cellsidentical to the original

cell Cells are diploid (2n)

Chromosomes duringMetaphase of mitosis

Prophase Metaphase Anaphase TelophaseCytokinesis

Mitosis Animation



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M tos s n mat onName each stage as you see it occur?

Mitosis in Onion Root Tips



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M n n n p

Do you see any stages of mitosis?



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Test Yourself

over Mitosis

Mitosis Quiz



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Q

Mitosis Quiz



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Q

Name the Stages of Mitosis:



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g f Interphase

Early prophase

Mid-ProphaseLateProphase

Metaphase

LateAnaphase

Early Anaphase

EarlyTelophase,

Begincytokinesis

Late telophase,Advancedcytokinesis

Identify the Stages



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y g

Early, Middle, & Late Prophase

Late Prophase Metaphase Anaphase

Late Anaphase Telophase

Telophase &

Cytokinesis

?

? ? ?

? ? ?

Locate the Four Mitotic



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Locate the Four MitoticStages in Plants

Metaphase

Prophase

Anaphase

Telophase

Uncontrolled Mitosis



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If mitosis is notcontrolled, unlimitedcell division occurscausing cancerous

tumorsOncogenes are special

proteins thatincrease the chance

that a normal celldevelops into a tumorcell

Cancer cells



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Meiosis

Formation of Gametes (Eggs & Sperm)

Facts About Meiosis



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Preceded by interphase whichincludes chromosome replication

Two meiotic divisions --- Meiosis

I and Meiosis IICalled Reduction- division

Original cell is diploid (2n)

Four daughter cells produced thatare monoploid (1n)

Facts About Meiosis



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Daughter cells contain half the

number of chromosomes as theoriginal cell

Produces gametes (eggs & sperm)

Occurs in the testes in males(Spermatogenesis)

Occurs in the ovaries in females(Oogenesis)

More Meiosis Facts



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Start with 46 double strandedchromosomes (2n)After 1 division - 23 double

stranded chromosomes (n)After 2nd division - 23 singlestranded chromosomes (n)

Occurs in our germ cells thatproduce gametes

Why Do we Need Meiosis?



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y

It is the fundamental basis of

sexual reproductionTwo haploid (1n) gametes arebrought together through

fertilization to form a diploid(2n) zygote

Fertilization – “Putting itll h ”



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gall together”

1n =3

2n = 6

Replication of Chromosomes



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pReplication is the

process ofduplicating achromosome

Occurs prior todivision

Replicated copiesare called sister

chromatidsHeld together atcentromere

Occurs inInterphase

A Replicated Chromosome



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p

Homologs

(same genes,different alleles)

Sister

Chromatids (same genes,same alleles)

Gene X

Homologs separate in meiosis I andtherefore different alleles separate.

Meiosis Forms Haploid Gametes



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F m p mMeiosis must reduce the chromosome number

by halfFertilization then restores the 2n number

from mom from dad child

meiosis reduces

genetic content

too

much!

The right

number!

Meiosis: Two Part Cell



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Division

Homologsseparate

Sisterchromatidsseparate

Diploid

MeiosisI

MeiosisII

Diploid

Haploid

Meiosis I: Reduction Division



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Nucleus Spindlefibers Nuclear

envelopeEarly

Prophase I(Chromosomenumberdoubled)

LateProphaseI

MetaphaseI Anaphase

ITelophase I

(diploid)

Prophase I



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p

Early prophase

Homologs pair.Crossing overoccurs.

Late prophase

Chromosomes condense.Spindle forms.Nuclear envelopefragments.

Tetrads Form in Prophase I



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p

Homologous chromosomes

(each with sister

chromatids)

Join to form a TETRAD

Called Synapsis

Crossing-Over



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gHomologous

chromosomes ina tetrad crossover each other

Pieces of

chromosomes orgenes areexchanged

Produces

Geneticrecombination inthe offspring

Homologous Chromosomes



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gDuring Crossing-Over

Crossing-Over



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Crossing-over multiplies the already hugenumber of different gamete types

produced by independent assortment

Metaphase I



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Homologous pairs of chromosomesalign along theequator of the

cell

Anaphase I



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Homologs separate and

move to opposite poles.

Sister chromatids remain

attached at their centromeres.

Telophase I



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Nuclear envelopesreassemble.

Spindle disappears.

Cytokinesis divides cellinto two.

Meiosis II



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Only one homolog of each

chromosome is present inthe cell.

Meiosis II produces gametes withone copy of each chromosome andthus one copy of each gene.

Sister chromatids carry

identical geneticinformation.

Gene X

Meiosis II: Reducing



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Chromosome Number

ProphaseII MetaphaseII

AnaphaseII

TelophaseII 4 Identical

haploid cells

Prophase II



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Nuclear envelopefragments.

Spindle forms.

Metaphase II



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Chromosomes align

along equator of cell.

Anaphase II



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Sister chromatids separate andmove to oppositepoles.

Equator

Pole

Telophase II



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Nuclear envelopeassembles.

Chromosomesdecondense.

Spindle disappears.

Cytokinesis dividescell into two.

Results of Meiosis



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Gametes (egg & sperm)form

Four haploid cells withone copy of each

chromosome

One allele of each gene

Different combinationsof alleles for differentgenes along thechromosome



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Gametogenesis

Oogenesisor

Spermatogenesis

Spermatogenesis



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Occurs in the

testesTwo divisionsproduce 4

spermatidsSpermatids matureinto sperm

Men produce about250,000,000sperm per day

Spermatogenesis in theT t



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TestesSpermatid

Spermatogenesis



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Oogenesis

O h



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Occurs in the ovaries

Two divisions produce 3 polar bodies that die and 1 egg

Polar bodies die because of unequaldivision of cytoplasm

Immature egg called oocyte

Starting at puberty, one oocytematures into an ovum (egg) every 28days

Oogenesis in the Ovaries



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Oogenesis



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Oogonium(diploid)

Mitosis

Primaryoocyte(diploid)

Meiosis I

Secondaryoocyte(haploid)

Meiosis II(if fertilizationoccurs)

First polar bodymay divide

(haploid) Polarbodiesdie

Ovum (egg)

Secondpolar body(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Mature

egg

A

X

A

X



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Comparing

Mitosis andMeiosis

Mit sis M i sis

Comparison of Divisions



Mitosis Meiosis

Number ofdivisions

1 2

Number ofdaughter cells

2 4

Geneticallyidentical?

Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Germ cells

When Throughout life At sexual maturity

05. Cell Division

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