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Cellular Cellular DivisionDivision
By:By:Muhammad Iqbal KhanMuhammad Iqbal Khan
SS BiologySS BiologyGHSS Mochh MianwaliGHSS Mochh Mianwali
Email: Email: [email protected]# 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