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Cellular Cellular DivisionDivision

By:By:Muhammad Iqbal KhanMuhammad Iqbal Khan

SS BiologySS BiologyGHSS Mochh MianwaliGHSS Mochh Mianwali

Email: Email: mikhan1313@gmail.comMob# 0923015740044Mob# 0923015740044

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Cell DivisionCell DivisionAll cells are derived fromAll cells are derived from

pre-existingpre-existing cellscellsNew cells are produced for New cells are produced for

growthgrowth and to replace and to replace damaged damaged or old cellsor old cells

Differs inDiffers in prokaryotesprokaryotes (bacteria) and(bacteria) and eukaryoteseukaryotes (protists, fungi, plants, & (protists, fungi, plants, & animals)animals)

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Keeping Cells IdenticalKeeping Cells Identical

TheThe instructions for instructions for making cell partsmaking cell parts are encoded in are encoded in the the DNADNA, so each , so each new cell must get new cell must get aa complete set of complete set of the DNA the DNA moleculesmolecules

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DNA ReplicationDNA ReplicationDNA must be DNA must be

copied orcopied or replicated replicated before cell before cell divisiondivision

Each new cell Each new cell will then have will then have anan identical identical copycopy of the of the DNADNA

Original DNA Original DNA strandstrand

Two new, Two new, identical DNA identical DNA

strandsstrands

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Identical Daughter Identical Daughter CellsCells

Parent CellParent Cell

Two Two identical identical daughter daughter

cellscells

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ChromosomChromosomeses

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Prokaryotic ChromosomeProkaryotic ChromosomeThe DNA of The DNA of

prokaryotes prokaryotes (bacteria) is (bacteria) is one, circular one, circular chromosomechromosome attached to attached to the inside of the inside of the cell the cell membranemembrane

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Eukaryotic Eukaryotic ChromosomesChromosomesAll All eukaryoticeukaryotic cells store cells store

genetic information in genetic information in chromosomeschromosomes

Most eukaryotes have between Most eukaryotes have between 10 10 and 50 chromosomesand 50 chromosomes in their body in their body cellscells

Human body cellsHuman body cells have have 4646 chromosomes or 23 identical pairschromosomes or 23 identical pairs

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Eukaryotic Eukaryotic ChromosomesChromosomesEach chromosome is composed Each chromosome is composed

of a of a single,single, tightly coiled DNAtightly coiled DNA moleculemolecule

Chromosomes Chromosomes can’t be seencan’t be seen when cells when cells aren’t dividingaren’t dividing  and and are called are called chromatinchromatin

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Compacting DNA into Compacting DNA into ChromosomesChromosomes

DNA is tightly coiled around proteins called histones

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Chromosomes in Dividing Chromosomes in Dividing CellsCells

Duplicated chromosomes are called chromatids & are held together by the centromere

Called Sister Called Sister ChromatidsChromatids

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KaryotypeKaryotypeA A picturepicture of the of the

chromosomes chromosomes from a human from a human cell cell arranged in arranged in pairs by sizepairs by size

First 22 pairs are First 22 pairs are called called autosomesautosomes

Last pair are the Last pair are the sex chromosomessex chromosomes

XXXX female or female or XYXY malemale

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Boy or Girl?Boy or Girl?

Y - Y - ChromosomeChromosome

X - X - ChromosomeChromosome

The Y Chromosome The Y Chromosome DecidesDecides

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Cell Cell ReproductionReproduction

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Types of Cell Types of Cell ReproductionReproductionAsexual reproductionAsexual reproduction involves a involves a

single cellsingle cell dividing to make dividing to make 2 2 new, identical daughter cellsnew, identical daughter cells

Mitosis & binary fission Mitosis & binary fission are are examples of asexual reproductionexamples of asexual reproduction

Sexual reproductionSexual reproduction involves two involves two cells (egg & sperm) joining to cells (egg & sperm) joining to make a make a new cell (zygote)new cell (zygote) that is that is NOT identical to the original cellsNOT identical to the original cells

Meiosis Meiosis is an exampleis an example

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Cell Division in Cell Division in ProkaryotesProkaryotes

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Cell Division in Cell Division in ProkaryotesProkaryotes Prokaryotes such Prokaryotes such

as as bacteriabacteria divide divide into 2 identical into 2 identical cells by the process cells by the process of of binary fissionbinary fission

Single chromosome Single chromosome makes a copy of makes a copy of itselfitself

Cell wall forms Cell wall forms between the between the chromosomes chromosomes dividing the celldividing the cell

Parent Parent cellcell

2 identical daughter 2 identical daughter cellscells

ChromosoChromosome me

doublesdoubles

Cell Cell splitssplits

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Prokaryotic Cell Prokaryotic Cell Undergoing Binary Undergoing Binary

FissionFission

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Animation of Binary Animation of Binary FissionFission

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The Cell The Cell CycleCycle

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Five Phases of the Cell Five Phases of the Cell CycleCycle

GG11 - primary growth phase - primary growth phaseS – synthesis; DNA replicatedS – synthesis; DNA replicatedGG22 - secondary growth phase - secondary growth phase

collectively these 3 stages collectively these 3 stages are called interphaseare called interphase

M - mitosisM - mitosisC - cytokinesisC - cytokinesis

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Cell CycleCell Cycle

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Interphase - GInterphase - G11 Stage Stage

11stst growth stage growth stage after cell after cell divisiondivision

Cells Cells maturemature by making by making more cytoplasm & more cytoplasm & organellesorganelles

Cell carries on its Cell carries on its normal normal metabolic activitiesmetabolic activities

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Interphase – S StageInterphase – S StageSynthesisSynthesis stage stageDNADNA is copied or is copied or replicatedreplicated

Two Two identicidentic

al al copies copies of DNAof DNA

Original Original DNADNA

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Interphase – GInterphase – G22 Stage Stage22ndnd Growth Growth Stage StageOccurs Occurs after DNA has been copiedafter DNA has been copiedAll cell All cell structures needed for structures needed for

divisiondivision are made (e.g. are made (e.g. centrioles)centrioles)

Both Both organelles & proteinsorganelles & proteins are are synthesizedsynthesized

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What’s Happening in What’s Happening in Interphase?Interphase?What the cell looks likeWhat the cell looks like

Animal Cell

What’s occurring

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Sketch the Cell CycleSketch the Cell Cycle

DaughteDaughter Cellsr Cells

DNA DNA CopiedCopied

Cells Cells MaturMatur

ee

Cells prepare Cells prepare for Divisionfor Division

Cell Divides into Cell Divides into Identical cellsIdentical cells

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MitosisMitosis

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MitosisMitosisDivision of the Division of the

nucleusnucleusAlso called Also called

karyokinesiskaryokinesisOnly occurs in Only occurs in

eukaryoteseukaryotesHas Has fourfour stages stagesDoesn’t occur in Doesn’t occur in

some cells such some cells such as as brain cellsbrain cells

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Four Mitotic StagesFour Mitotic Stages

ProProphasephaseMetaMetaphasephaseAnaAnaphasephaseTeloTelophasephase

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Early ProphaseEarly ProphaseChromatinChromatin in nucleus condenses to in nucleus condenses to

form form visible chromosomesvisible chromosomesMitotic spindle Mitotic spindle forms from fibers in forms from fibers in

cytoskeleton or cytoskeleton or centrioles (animal)centrioles (animal)

ChromosomesChromosomes

NucleolusNucleolus CytoplasmCytoplasm

Nuclear MembraneNuclear Membrane

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Late ProphaseLate ProphaseNuclear membrane & nucleolusNuclear membrane & nucleolus

are broken downare broken downChromosomesChromosomes continue continue

condensing & are condensing & are clearly visibleclearly visibleSpindle fibers called Spindle fibers called

kinetochoreskinetochores attach to the attach to the centromerecentromere of each chromosome of each chromosome

SpindleSpindle finishes forming finishes forming between the between the poles of the cellpoles of the cell

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Late ProphaseLate Prophase

Nucleus & Nucleolus have disintegratedNucleus & Nucleolus have disintegrated

ChromosomeChromosomes s

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Spindle Fiber attached to Spindle Fiber attached to ChromosomeChromosome

Kinetochore Kinetochore FiberFiber

ChromosomeChromosome

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Review of ProphaseReview of Prophase

What the cell What the cell looks likelooks like

What’s happeningWhat’s happening

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Spindle FibersSpindle FibersThe mitotic The mitotic spindlespindle form from the form from the

microtubulesmicrotubules in plantsin plants and and centrioles in animal cellscentrioles in animal cells

Polar fibers Polar fibers extend from one pole extend from one pole of the cell to the opposite poleof the cell to the opposite pole

Kinetochore fibersKinetochore fibers extend from extend from the pole to the centromere of the the pole to the centromere of the chromosome to which they attachchromosome to which they attach

AstersAsters are short fibers radiating are short fibers radiating from centriolesfrom centrioles

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Sketch The SpindleSketch The Spindle

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MetaphaseMetaphaseChromosomes, attached to the Chromosomes, attached to the

kinetochore fiberskinetochore fibers, move to the , move to the center of the cellcenter of the cell

Chromosomes are now lined up at Chromosomes are now lined up at the equatorthe equator

Pole of Pole of the Cellthe Cell

Equator of CellEquator of Cell

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MetaphaseMetaphase

ChromosoChromosomes lined mes lined at the at the EquatorEquator

Asters at Asters at the polesthe poles

Spindle Spindle FibersFibers

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MetaphaseMetaphase

AsterAster

Chromosomes at EquatorChromosomes at Equator

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Review of MetaphaseReview of Metaphase

What the cell What the cell looks likelooks like

What’s What’s occurringoccurring

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AnaphaseAnaphaseOccurs Occurs rapidlyrapidlySister Sister

chromatidschromatids are pulled are pulled apart to apart to opposite polesopposite poles of the cell by of the cell by kinetochore kinetochore fibersfibers

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AnaphaseAnaphase

Sister Sister ChromatidChromatid

s being s being separatedseparated

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Anaphase ReviewAnaphase Review

What What the cell the cell looks looks likelike

What’s What’s occurrioccurri

ngng

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TelophaseTelophaseSister chromatids at Sister chromatids at opposite opposite polespoles

Spindle Spindle disassemblesdisassemblesNuclear envelopeNuclear envelope forms forms around each set of sister around each set of sister chromatidschromatids

NucleolusNucleolus reappears reappearsCYTOKINESISCYTOKINESIS occurs occursChromosomes reappear as Chromosomes reappear as chromatinchromatin

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Comparison of Anaphase & Comparison of Anaphase & TelophaseTelophase

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CytokinesisCytokinesisMeans division of the Means division of the

cytoplasmcytoplasmDivisionDivision of cell into two, of cell into two,

identical halves called identical halves called daughter cellsdaughter cells

In plant cells, cell plate In plant cells, cell plate forms forms at the equator to divide cellat the equator to divide cell

In animal cells, In animal cells, cleavage cleavage furrow forms to split cellfurrow forms to split cell

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CytokinesisCytokinesisCleavage Cleavage furrow in furrow in

animal cellanimal cell

Cell plate in Cell plate in animal cellanimal cell

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Mitotic StagesMitotic Stages

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Daughter Cells of MitosisDaughter Cells of MitosisHave the Have the same number of same number of

chromosomes as each otherchromosomes as each other and as the parent celland as the parent cell from from which they were formedwhich they were formed

IdenticalIdentical to each other, but to each other, but smaller than parent cellsmaller than parent cell

Must Must grow in sizegrow in size to become to become mature cells mature cells (G(G11 of Interphase) of Interphase)

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Identical Daughter CellsIdentical Daughter Cells

Chromosome number the Chromosome number the samesame, but , but cells cells smallersmaller than parent cell than parent cell

What What is the is the 2n or 2n or

diploid diploid numbenumbe

r?r?22

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RevieReview of w of

MitosiMitosiss

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Draw & Learn these Draw & Learn these StagesStages

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Draw & Learn these Draw & Learn these StagesStages

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InterphaseInterphase

ProphaseProphase

MetaphaseMetaphaseAnaphaseAnaphase

TelophaseTelophase

Name the Mitotic Stages:Name the Mitotic Stages:

Name Name this?this?

Name this?Name this?

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Eukaryotic Cell DivisionEukaryotic Cell Division Used for Used for growth and growth and

repairrepair Produce two new cells Produce two new cells

identical to the original identical to the original cellcell

Cells are Cells are diploid (2n)diploid (2n)Chromosomes Chromosomes

during Metaphase during Metaphase of mitosisof mitosis

ProphaProphasese

MetaphaseMetaphase AnaphaseAnaphaseTelophaseTelophaseCytokinesisCytokinesis

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Mitosis AnimationMitosis AnimationName each stage as you see it Name each stage as you see it

occur?occur?

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Mitosis in Onion Root Mitosis in Onion Root TipsTips

Do you see any stages of mitosis?Do you see any stages of mitosis?

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Test Yourself Test Yourself over Mitosisover Mitosis

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Mitosis QuizMitosis Quiz

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Mitosis QuizMitosis Quiz

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Name the Stages of Name the Stages of Mitosis:Mitosis:

Interphase

Early prophase

Mid-ProphaseLate Prophase

Metaphase

Late Anaphase

Early Anaphase

Early Telophase

, Begin

cytokinesis

Late telophase, Advanced cytokinesis

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Identify the StagesIdentify the Stages

Early, Middle, & Late Prophase Early, Middle, & Late Prophase

Late Late ProphaseProphase

MetaphaseMetaphase AnaphaseAnaphase

Late Late AnaphaseAnaphase

TelophaseTelophase Telophase & Telophase & CytokinesisCytokinesis

??

?? ?? ??

?? ?? ??

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Locate the Four Mitotic Locate the Four Mitotic Stages in PlantsStages in Plants

MetaphasMetaphasee

ProphaseProphase

AnaphaAnaphasese TelophaseTelophase

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Uncontrolled Mitosis If mitosis is not If mitosis is not

controlledcontrolled, , unlimited cell unlimited cell division occurs division occurs causing cancerous causing cancerous tumorstumors

OncogenesOncogenes are are special proteins special proteins that increase the chance increase the chance that a normal cell that a normal cell develops into adevelops into a tumor cell tumor cell

Cancer Cancer cellscells

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MeiosisMeiosisFormation of Formation of

GametesGametes (Eggs & (Eggs & Sperm)Sperm)

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Facts About MeiosisFacts About MeiosisPreceded by interphase which Preceded by interphase which

includesincludes chromosome chromosome replicationreplication

TwoTwo meiotic divisions --- meiotic divisions --- Meiosis I and Meiosis IIMeiosis I and Meiosis II

Called Reduction- divisionCalled Reduction- divisionOriginal cell is diploid (2n)Original cell is diploid (2n)Four daughter cellsFour daughter cells produced produced

that are that are monoploid (1n)monoploid (1n)

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Facts About MeiosisFacts About MeiosisDaughter cellsDaughter cells contain half the contain half the

number of chromosomesnumber of chromosomes as the as the original celloriginal cell

ProducesProduces gametesgametes (eggs & (eggs & spermsperm))

Occurs in the Occurs in the testestestes in males in males ((SpermatogenesisSpermatogenesis))

Occurs in the Occurs in the ovariesovaries in in females (females (OogenesisOogenesis))

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Start with Start with 46 double stranded 46 double stranded chromosomes (2n)chromosomes (2n)After 1 division - After 1 division - 23 double 23 double stranded chromosomes (n)stranded chromosomes (n)After 2nd division - After 2nd division - 23 single 23 single stranded chromosomes (n)stranded chromosomes (n)  Occurs in our Occurs in our germ cellsgerm cells that that produce gametesproduce gametes

More Meiosis FactsMore Meiosis Facts

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Why Do we Need Why Do we Need Meiosis?Meiosis?

It is the fundamental basis It is the fundamental basis of of sexual reproductionsexual reproduction

Two haploid (1n) gametes Two haploid (1n) gametes are brought together are brought together through through fertilizationfertilization to form to form a diploid a diploid (2n) zygote(2n) zygote

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Fertilization – “Putting Fertilization – “Putting it all together”it all together”

1n =31n =3

2n = 62n = 6

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Replication of Replication of ChromosomesChromosomes

ReplicationReplication is the is the process of process of duplicating a duplicating a chromosomechromosome

Occurs Occurs prior to prior to divisiondivision

Replicated Replicated copies are called copies are called sister chromatidssister chromatids

Held together at Held together at centromerecentromere

Occurs in Occurs in InterphasInterphas

ee

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A Replicated A Replicated ChromosomeChromosome

HomologsHomologs (same genes, (same genes, different alleles)different alleles)

SisterSisterChromatidsChromatids(same genes,(same genes,same alleles)same alleles)

Gene XGene X

Homologs separate in meiosis I and Homologs separate in meiosis I and therefore different alleles separate.therefore different alleles separate.

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Meiosis Forms Haploid Meiosis Forms Haploid GametesGametes

Meiosis must Meiosis must reduce the chromosome number by halfreduce the chromosome number by half Fertilization then restoresFertilization then restores the 2n number the 2n number

from mom from dad child

meiosis reducesgenetic content

toomuch!

The right number!

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Meiosis: Two Part Cell Meiosis: Two Part Cell DivisionDivision

HomologsHomologsseparateseparate

Sister Sister chromatidschromatidsseparateseparate

DiploidDiploid

MeiosisMeiosis I I

MeiosisMeiosisIIII

DiploidDiploid

HaploiHaploidd

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Meiosis I: Reduction DivisionMeiosis I: Reduction Division

NucleusNucleus SpindleSpindlefibersfibers NuclearNuclear

envelopeenvelopeEarly Early Prophase IProphase I(Chromoso(Chromosome number me number

doubleddoubled))

Late Late ProphasProphas

e Ie I

MetaphaMetaphase Ise I AnaphasAnaphas

e Ie ITelophase Telophase I I (diploid)(diploid)

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Prophase IProphase I

Early Early prophaseprophaseHomologs Homologs pair.pair.Crossing over Crossing over occursoccurs.

Late prophaseLate prophaseChromosomes Chromosomes condense.condense.Spindle forms.Spindle forms.Nuclear envelope Nuclear envelope fragments.fragments.

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Tetrads Form in Tetrads Form in Prophase IProphase I

Homologous Homologous chromosomeschromosomes

(each with sister chromatids) (each with sister chromatids)   

Join to form aJoin to form a TETRADTETRAD

Called SynapsisCalled Synapsis

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Crossing-OverCrossing-Over Homologous Homologous

chromosomeschromosomes in a tetrad in a tetrad cross over each cross over each otherother

Pieces of Pieces of chromosomes chromosomes or or genes are genes are exchangedexchanged

Produces Produces Genetic Genetic recombinationrecombination in the offspringin the offspring

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Homologous Homologous Chromosomes During Chromosomes During

Crossing-OverCrossing-Over

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Crossing-over multiplies the already Crossing-over multiplies the already huge number of different gamete huge number of different gamete types produced by independent types produced by independent

assortmentassortment

Crossing-OverCrossing-Over

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Metaphase IMetaphase I

Homologous Homologous pairspairs of of

chromosomes chromosomes align along the align along the equatorequator of the of the

cellcell

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Anaphase IAnaphase I

Homologs separateHomologs separate and move to opposite and move to opposite poles.poles.

Sister chromatids Sister chromatids remain remain attached attached at theirat their centromerescentromeres.

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Telophase ITelophase I

Nuclear envelopes Nuclear envelopes reassemble.reassemble.

Spindle disappears.Spindle disappears.

Cytokinesis Cytokinesis divides cell divides cell into two.into two.

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Meiosis IIMeiosis IIOnly one homolog of Only one homolog of

each chromosome is each chromosome is present in the cellpresent in the cell.

Meiosis II produces gametes Meiosis II produces gametes with with one copy of each chromosome one copy of each chromosome and thus one copy of each and thus one copy of each gene.gene.

Sister chromatids carry Sister chromatids carry identical genetic identical genetic informationinformation. .

Gene XGene X

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Meiosis II: Reducing Meiosis II: Reducing Chromosome NumberChromosome Number

Prophase Prophase IIII MetaphaMetapha

se IIse IIAnaphasAnaphas

e IIe II

TelophasTelophase IIe II 4 Identical 4 Identical

haploid haploid cellscells

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Prophase IIProphase II

Nuclear Nuclear envelope envelope fragments.fragments.

Spindle forms.Spindle forms.

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Metaphase IIMetaphase II

Chromosomes align Chromosomes align along along equatorequator of cell of cell..

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Anaphase IIAnaphase II

Sister Sister chromatidschromatids separate and separate and move to move to opposite polesopposite poles.

EquatorEquator

PolePole

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Telophase IITelophase II

Nuclear envelope Nuclear envelope assembles.assembles.

Chromosomes Chromosomes decondense.decondense.

Spindle Spindle disappears.disappears.

Cytokinesis Cytokinesis divides cell into divides cell into two.two.

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Results of MeiosisResults of MeiosisGametes (egg & Gametes (egg & sperm) formsperm) form

Four haploid cells Four haploid cells with one copy of each with one copy of each chromosome chromosome

One allele of each One allele of each genegene

Different Different combinations of combinations of alleles for different alleles for different genes along the genes along the chromosomechromosome

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GametogenesisGametogenesisOogenesisOogenesis

or or Spermatogenesis Spermatogenesis

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SpermatogenesisSpermatogenesisOccurs in the Occurs in the

testestestesTwo divisions Two divisions

produce 4 produce 4 spermatidsspermatids

Spermatids Spermatids mature into spermmature into sperm

Men produce Men produce about about 250,000,000 250,000,000 sperm per daysperm per day

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Spermatogenesis in the Spermatogenesis in the TestesTestes

SpermatiSpermatidd

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SpermatogenesisSpermatogenesis

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OogenesisOogenesisOccurs in the Occurs in the ovariesovariesTwo divisions produce Two divisions produce 3 polar 3 polar

bodiesbodies that die and that die and 1 egg1 eggPolar bodies die because of Polar bodies die because of

unequal division of cytoplasmunequal division of cytoplasmImmature egg called Immature egg called oocyteoocyteStarting at puberty, one oocyte Starting at puberty, one oocyte

matures into an matures into an ovum (egg)ovum (egg) every 28 daysevery 28 days

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Oogenesis in the OvariesOogenesis in the Ovaries

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OogenesisOogenesis

OogoniumOogonium(diploid)(diploid)

MitosisMitosis

PrimaryPrimaryoocyteoocyte(diploid)(diploid)

Meiosis IMeiosis I

SecondarySecondaryoocyteoocyte(haploid)(haploid)

Meiosis IIMeiosis II(if fertilization(if fertilizationoccurs)occurs)

First polar bodyFirst polar bodymay divide may divide (haploid)(haploid) PolarPolar

bodiesbodiesdiedie

Ovum (egg)Ovum (egg)

SecondSecondpolar bodypolar body(haploid)(haploid)

a

A

X

X

a

X

A X

a

X

a

X

MatureMatureeggegg

A

X

A

X

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Comparing Comparing Mitosis and Mitosis and

MeiosisMeiosis

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MitosisMitosis MeiosisMeiosisNumber of Number of

divisionsdivisions 11 22

Number of Number of daughter cellsdaughter cells 22 44

Genetically Genetically identical?identical? YesYes NoNo

Chromosome #Chromosome # Same as Same as parentparent Half of parentHalf of parent

WhereWhere Somatic cellsSomatic cells Germ cellsGerm cells

WhenWhen Throughout Throughout lifelife

At sexual At sexual maturitymaturity

RoleRole Growth and Growth and repairrepair

Sexual Sexual reproductionreproduction

Comparison of DivisionsComparison of Divisions

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Cell Division

Mitosis & Meiosis

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Cell Division

What is it?

Why do Cells do it?

Why is it important to

me?

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Cell Division

Also known as Mitosis

Takes place in Regular Body Cells

Keeps Cells Living and Growing

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Phases of Mitosis

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Mitosis

The Basic Phases of a Cell’s Life:

•Interphase

•Prophase

•Metaphase

•Anaphase

•Telophase

•Cytokinesis

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Interphase

The longest stage of a Cell’s life

The time spent between divisions

Produces all materials required

for growth

Preparation for division

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Part of Interphase is also known as the G1 Phase of the Cell Cycle

(Growth Phase)

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The Second part of Interphase is known as the S Phase of the Cell Cycle

(Synthesis Phase – when DNA duplicates)

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The third part of the Cell Cycle, G2, is just a checkpoint to make sure the DNA is correct.

Next step –

Mitosis

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Mitosis:Cell Division

The last part of the Cell Cycle is called Mitosis and has 4 phases during which the cell divides into 2 cells

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ProphaseThe Cell begins

the division process

1.The nucleolus disappears,

2.The nuclear membrane breaks apart

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3. The chromosomes become visible

4. The spindle apparatus forms and attaches to the centromeres of the chromosomes

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Metaphase

The Second Phase of Mitosis

1.The Nuclear Membrane is completely gone

2. The duplicated chromosomes line up along the cell's equator.

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Anaphase

The third phase of Mitosis

Diploid sets of daughter chromosomes separate

They are pushed and pulled toward opposite poles of the cell by the spindle fibers

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Spindle Fibers

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Telophase

The nuclear membrane and nucleoli (nucleus) reform.

Cytokinesis is nearly complete,

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The Cell Plate begins to form

The Cell prepares for finial division

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Cytokinesis – The final stage of Mitosis

The cytoplasm, organelles, and nuclear material are evenly split and two new cells are formed.

Cell Plate

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The two new cells – each exactly like the other – are called Daughter Cells

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Quick Review:

The following slides are drawings of the stages of Mitosis. On your notes, please draw each phase and label it.

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Interphase – The Cell spends the majority of its life here, growing and functioning. During the S Phase of the Cell Cycle, the DNA replicates, in anticipation of Mitosis

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In Early Prophase of Mitosis the Chromosomes get small, centrioles move to the poles of the nucleus, and spindle fibers develop

Pair of Centrioles

Spindle Fibers

Chromosomes consisting of 2 Sister Chromatids

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Late Prophase happens when the Nuclear Envelope disintegrates and spindle fibers begin to move Chromosomes toward the center of cell.

Spindle Fibers

Chromosomes

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During Metaphase the Chromosomes line up across center of the cell, also called the equator, or Metaphase plate.

Spindle Fibers

Chromosomes

Equator, or Metaphase Plate

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In Anaphase the Chromatids that make up each Chromosome move apart and travel to opposite ends of cellular spindle

Daughter Chromosomes

Chromosome

Chromatid

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In Telophase an envelope surrounds each set of Chromatids to form new Nucleus and the Cytoplasm starts to divide

Cleavage Furrow

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Cytokinesis takes place when the Cytoplasm divides and two cells with identical genetic material are formed

Daughter Cells

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A B C

D E

Quick Review – Place Cells in Mitosis Order

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Quick Review: Identify What happens in each phase of Mitosis:Prophase

Metaphase

Anaphase

Telophase

Interphase

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Why Do Cells Divide?

The larger a cell becomes, the more demands the cell places on it's DNA.

It also has more trouble moving enough food and wastes across its cell membrane.

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The bigger the cell gets the harder it becomes to move food and waste across the membrane

Food goes in

Waste goes out

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This happens because the surface area and volume ratio does not stay the same as the cell size increases.

Protein Pumps

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The cell's ability to either get substances from the outside or eliminate waste from the inside is related to the surface area of the cell membrane. (outside)

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How much food and other material is required, and how much waste the cell produces and has to get rid of, is related to the volume of the cell. (inside)

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As a cell gets bigger there comes a time when its surface area is not large enough to meet the demands of the cell's volume and the cell stops growing.

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So, once cells reach a certain size they must divide in order to continue to function – or they will no longer be able to take in nutrients and eliminate waste.

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Why Is Cell Division Important?

1. All Living Things are made of Cells

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2. The Cell is the basic unit of Structure and Function in Living Things.

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3. All Cells come from pre existing Cells

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You are a living organism, made of cells.

In order to keep living, your cells must stay alive.

In order for cells to keep living, they must divide and multiply

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Meiosis

Why We Are Who We Are

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MeiosisTakes place in the Gametes of an organism

People have a Chromosome count of 46

When an egg joins a sperm the count must stay at 46 to remain human

So, the egg can only have 23 chromosomes, and the sperm can only have 23 chromosomes

But, the integrity of the organism must be maintained.

How does this happen?

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During Meiosis gamete (sex) cells undergo a “double division”, maintaining the DNA, but reducing the chromosomal count to 23

+ =

Sperm (23) + Egg (23) = Fertilized Cell (46)

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Chromosome after S Phase

Chromosomes at beginning of Mitosis

After Mitosis

After Meiosis

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Original Gamete Metaphase Anaphase Telophase Cytokinesis

2 Daughter Cells Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis – 4 Gametes

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At the end of Meiosis the individual Gamete cell has divided from one cell to four.

Males produce 4 viable sperm.

Females produce 1 viable egg and 3 non functioning polar bodies.

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SPERMATOGENESIS

OOGENESIS

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Meiosis ensures that

all living organisms

will maintain both Genetic Diversity and

Genetic Integrity

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Catherine PattersonSanta Rita High School

Tucson, Arizona

2008