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ASSIGNMENT # 03• Prepared by Amjad Khan• Submitted to Dear, Sir Ghadir Ali• Program BS Microbiology 3th • Subject CELL BIOLOGY• Topic CELL CYCLE• Date 12th January, 2015

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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 new, 2 new, identical daughter cellsidentical 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 make a cells (egg & sperm) joining to make a new cell (zygote)new cell (zygote) that is that is NOT NOT identical to the original cellsidentical to the original cellsMeiosisMeiosis is an exampleis an example

Division Mechanisms

Prokaryotic organisms

– Binary fission

Eukaryotic organisms

– Mitosis• Karyokinesis (division of nucleus)

• Cytokinesis (division of cytoplasm)

– Meiosis

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CEll dIvISIoN IN CEll dIvISIoN IN pRokARyoTESpRokARyoTES

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Cell Division in ProkaryotesCell Division in Prokaryotes Prokaryotes such as Prokaryotes such as

bacteriabacteria divide into 2 divide into 2 identical cells by the identical cells by the process of process of binary binary fissionfission

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

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

Parent Parent cellcell

2 identical daughter cells2 identical daughter cells

Chromosome Chromosome doublesdoubles

Cell splitsCell splits

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Prokaryotic Cell Prokaryotic Cell Undergoing Binary FissionUndergoing Binary Fission

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Animation of Binary FissionAnimation of Binary Fission

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TheThe CellCell CycleCycle

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Five Phases of the Cell CycleFive Phases of the Cell Cycle

GG11 - primary growth/gap phase - primary growth/gap phaseS – synthesis; DNA replicatedS – synthesis; DNA replicatedGG22 - secondary growth/gap - secondary growth/gap phase phase collectively these 3 stages are collectively these 3 stages are called called interphaseinterphase

M - mitosisM - mitosisC - cytokinesisC - cytokinesis

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Cell CycleCell Cycle

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Interphase - GInterphase - G11 Stage Stage

11stst growth/gap stage growth/gap stage after cell after cell divisiondivision

Cells Cells maturemature by making more by making more cytoplasm & organellescytoplasm & organelles

Cell carries on its Cell carries on its normal normal metabolic activities metabolic activities i.e. i.e. respiration, digestion etc.respiration, digestion etc.

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

Two Two identical identical copies copies of DNAof DNA

Original Original DNADNA

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Interphase – GInterphase – G22 Stage Stage22ndnd Growth/Gap Growth/Gap Stage StageOccurs Occurs after DNA has been copie; after DNA has been copie; also in preparation for M phasealso in preparation for M phase

All cell All cell structures needed for structures needed for divisiondivision are made (e.g. centrioles) are made (e.g. centrioles)

Both Both organelles & proteinsorganelles & proteins are are synthesizedsynthesized

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What’s Happening in Interphase?What’s Happening in 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

Daughter Daughter CellsCells

DNA CopiedDNA Copied

Cells Cells MatureMature

Cells prepare for Cells prepare for DivisionDivision

Cell Divides into Cell Divides into Identical cellsIdentical cells

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MitosisMitosis

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MitosisMitosisDivision of the Division of the

nucleus nucleus (karyokinesis)(karyokinesis)

Division of the Division of the cytoplasm cytoplasm (cytokinesis)(cytokinesis)

Only occurs in Only occurs in eukaryoteseukaryotes

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

some cells such as some cells such 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 chromosomes

Mitotic 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 are broken downbroken down

ChromosomesChromosomes continue condensing & continue condensing & are are clearly visibleclearly visible

Spindle fibers called Spindle fibers called kinetochoreskinetochores attach to the centromereattach to the centromere of each of each chromosomechromosome

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

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Late ProphaseLate Prophase

Nucleus & Nucleolus have disintegratedNucleus & Nucleolus have disintegrated

Chromosomes Chromosomes

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Spindle Fiber attached to Spindle Fiber attached to ChromosomeChromosome

Kinetochore FiberKinetochore Fiber

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 centrioles in animal cellsin animal cells

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

Kinetochore fibersKinetochore fibers extend from the extend from the pole to the centromere of 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 center , move to the center of the cellof the cell

Chromosomes are now lined up at the Chromosomes are now lined up at the equatorequator

Pole of Pole of the Cellthe Cell

Equator of CellEquator of Cell

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MetaphaseMetaphase

AsterAster

Chromosomes at EquatorChromosomes at Equator

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Review of MetaphaseReview of Metaphase

What the cell looks What the cell looks likelike

What’s What’s occurringoccurring

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AnaphaseAnaphaseOccurs Occurs rapidlyrapidlySister Sister chromatidschromatids are are pulled apart to pulled apart to opposite polesopposite poles of the cell by of the cell by kinetochore kinetochore fibersfibers

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Anaphase ReviewAnaphase Review

What the What the cell looks cell looks

likelike

What’s What’s occurringoccurring

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TelophaseTelophaseSister chromatids at Sister chromatids at opposite opposite polespoles

Spindle Spindle disassemblesdisassemblesNuclear envelopeNuclear envelope forms around forms around each set of sister chromatidseach set of sister chromatids

NucleolusNucleolus reappears reappearsCYTOKINESISCYTOKINESIS occurs occursChromosomes reappear as Chromosomes reappear as chromatinchromatin

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Comparison of Anaphase & TelophaseComparison of Anaphase & Telophase

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CytokinesisCytokinesisMeans division of the cytoplasmMeans division of the cytoplasmDivisionDivision of cell into two, of cell into two, identical halves called identical halves called daughter daughter cellscells

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 furrow cleavage furrow forms to split cellforms to split cell

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CytokinesisCytokinesis

Cleavage furrow Cleavage furrow in animal cellin animal 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 and as the parent cellthe parent cell from which they from which they were formedwere formed

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

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

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Identical Daughter CellsIdentical Daughter Cells

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

What is What is the 2n the 2n

or or diploid diploid

number?number?

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Review Review of of

MitosisMitosis

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Draw & Learn these StagesDraw & Learn these Stages

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Draw & Learn these StagesDraw & Learn these Stages

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InterphaseInterphase

ProphaseProphase

MetaphaseMetaphaseAnaphaseAnaphase

TelophaseTelophase

Name the Mitotic Stages:Name the Mitotic Stages:

Name this?Name 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 during Chromosomes during Metaphase of mitosisMetaphase of mitosis

ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophaseCytokinesisCytokinesis

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

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Mitosis in Onion Root TipsMitosis in Onion Root TipsDo you see any stages of mitosis?Do you see any stages of mitosis?

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

MetaphaseMetaphase

ProphaseProphase

AnaphaseAnaphase

TelophaseTelophase

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Uncontrolled Mitosis If mitosis is not If mitosis is not

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

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

Cancer cellsCancer cells

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MeiosisMeiosisFormation of GametesFormation of Gametes

(Eggs & Sperm)(Eggs & Sperm)

Words to knoWGametes - reproductive cells that unite during sexual

reproduction to form a new cell called a zygote (male = sperm, female = egg cell)

Germ cells – sperm or egg cells

Somatic cells - any cell other than the reproductive cells

Diploid - a cell that contains two sets of chromosomes (2n), as normally found in somatic cells

Haploid - have one set of chromosomes (n=1) as in germ cells, or half as many as a somatic cell

Homologous – chromosomes that are alike in structure and genes

Alleles – different forms of a gene ex. if talking about hair color as the gene, different alleles would be different colors like red, blonde, black etc. 50

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Facts About MeiosisFacts About MeiosisPreceded by interphase which Preceded by interphase which includesincludes chromosome replicationchromosome replication

TwoTwo meiotic divisions: meiotic divisions: Meiosis I Meiosis I and Meiosis IIand Meiosis II

AkaAka reduction-divisionreduction-divisionOriginal cell is diploid (2n)Original cell is diploid (2n)Four daughter cellsFour daughter cells produced that produced that are are haploid (n)haploid (n)

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

of chromosomesof chromosomes as the original cellas the original cellProducesProduces gametesgametes (eggs & sperm(eggs & sperm))Occurs in the Occurs in the testestestes in males in males

((SpermatogenesisSpermatogenesis))Occurs in the Occurs in the ovariesovaries in females in females

((OogenesisOogenesis))Human diploid cells have Human diploid cells have 46 chromosomes 46 chromosomes

(2n=46)(2n=46)Human sperm and egg cells have Human sperm and egg cells have 23 23

chromosomes (n=23) eachchromosomes (n=23) each

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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

More Meiosis FactsMore Meiosis Facts

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Why Do we Need Meiosis?Why Do we Need Meiosis?It is the fundamental basis of It is the fundamental basis of sexual reproductionsexual reproduction

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

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

1n =31n =3

2n = 62n = 6

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Replication of ChromosomesReplication of ChromosomesReplicationReplication is the is the

process of process of duplicating a duplicating a chromosomechromosome

Occurs Occurs prior to prior to divisiondivision

Replicated copies Replicated copies are called are called sister sister chromatidschromatids

Held together at Held together at centromerecentromere

Occurs in Occurs in InterphaseInterphase

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A Replicated ChromosomeA Replicated Chromosome

HomologuesHomologues (same genes, (same genes, different alleles)different alleles)

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

Gene XGene X

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

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Meiosis Forms Haploid GametesMeiosis Forms Haploid GametesMeiosis must Meiosis must reduce the chromosome number reduce the chromosome number

by halfby 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

HomologuesHomologuesseparateseparate

Sister Sister chromatidschromatidsseparateseparate

DiploidDiploid

MeiosisMeiosis I I

MeiosisMeiosisIIII

DiploidDiploid

HaploidHaploid

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Meiosis I: Reduction DivisionMeiosis I: Reduction Division

NucleusNucleus SpindleSpindlefibersfibers NuclearNuclear

envelopeenvelopeEarly Early Prophase IProphase I

(Chromosome (Chromosome number number doubleddoubled))

Late Late Prophase Prophase

II

Metaphase Metaphase II Anaphase Anaphase

IITelophase I Telophase I

(diploid)(diploid)

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Prophase IProphase I

Early prophaseEarly prophaseHomologues Homologues pair.pair.Crossing over Crossing over occursoccurs.

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

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Tetrads Form in Prophase ITetrads Form in Prophase I

Homologous chromosomesHomologous chromosomes(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 in a tetrad tetrad cross over cross over each othereach other

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

Produces Produces Genetic Genetic recombinationrecombination in in the offspringthe offspring

•Occurs in nonsister chromatids•Increases genetic variability

Genetic recombination in which a strand of the genetic material (DNA/RNA)is broken and then joined to the end of a different DNA molecule.

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Homologous Chromosomes Homologous Chromosomes During Crossing-OverDuring Crossing-Over

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

produced by independent assortmentproduced by independent assortment

Crossing-OverCrossing-Over

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Metaphase IMetaphase I

Homologous pairsHomologous pairs of chromosomes of chromosomes align along the align along the equatorequator of the of the

cellcell

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Anaphase IAnaphase I

Homologues separateHomologues separate and and move to opposite poles.move to opposite 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 homologue of each Only one homologue of each

chromosome is present in chromosome is present in the cellthe cell.

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

Metaphase Metaphase IIII

Anaphase Anaphase IIII

Telophase Telophase IIII 4 Identical 4 Identical

haploid cellshaploid cells

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Prophase IIProphase II

Nuclear envelope Nuclear 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 chromatidsSister chromatids separate and separate and move to move to opposite opposite polespoles.

EquatorEquator

PolePole

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Telophase IITelophase II

Nuclear envelope Nuclear envelope assembles.assembles.

Chromosomes Chromosomes decondense.decondense.

Spindle disappears.Spindle disappears.

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

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Results of MeiosisResults of MeiosisGametes (egg & sperm) Gametes (egg & sperm) formform

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

One allele of each geneOne allele of each gene

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

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GametogenesisGametogenesisOogenesisOogenesis

oror SpermatogenesisSpermatogenesis

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SpermatogenesisSpermatogenesisOccurs in the Occurs in the

testestestesTwo divisions Two divisions

produce 4 produce 4 spermatidsspermatids

Spermatids Spermatids mature mature into sperminto sperm

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

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Spermatogenesis in the Spermatogenesis in the TestesTestes

SpermatidSpermatid

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SpermatogenesisSpermatogenesis

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OogenesisOogenesisOccurs in the Occurs in the ovariesovariesTwo divisions produce Two divisions produce 3 polar bodies3 polar bodies that die and that die and 1 egg1 egg

Polar bodies die because of Polar bodies die because of unequal unequal division of cytoplasmdivision of cytoplasm

Immature 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 every 28 daysdays

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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

divisionsdivisions11 22

Number of Number of daughter cellsdaughter cells 22 44

Genetically Genetically identical?identical?

YesYes NoNo

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

WhereWhere Somatic cellsSomatic cells Reproductive cellsReproductive cells

WhenWhen Throughout lifeThroughout life At sexual maturityAt sexual maturity

RoleRole Growth and Growth and repairrepair

Sexual reproductionSexual reproduction

Comparison of DivisionsComparison of Divisions

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Meiosis Mitosis

Definition:

A type of cellular reproduction in which the number of chromosomes are reduced by half through the separation of homologous chromosomes in a diploid cell.

A process of asexual reproduction in which the cell divides in two producing a replica, with an equal number of chromosomes in haploid cell

Function: sexual reproduction Cellular Reproduction & general growth and repair of the body

Type of Reproduction: Sexual AsexualOccurs in: Humans, animals, plants, fungi all organismsGenetically: different identical

Crossing Over: Yes, mixing of chromosomes can occur. No, crossing over cannot occur.

Pairing of Homologues: Yes NoNumber of Divisions: 2 1Number of Haploid Daughter Cells produced:

4 2

Chromosome Number: Reduced by half Remains the same

Steps:

The steps of meiosis are Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II and Telophase II.

The steps of mitosis are Interphase, Prophase, Metaphase, Anaphase, Telophase and Cytokinesis

Karyokenesis: Occurs in Interphase I Occurs in Interphase

Cytokenesis: Occurs in Telophase I & Telohpase II Occurs in Telophase

Centromeres Split:The centromeres do not separate during anaphase I, but during anaphase II

The centromeres split during Anaphase

Creates: Sex cells only: Female egg cells or Male sperm cells

Makes everything other than sex cells

End…..

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