2. 2
Cell DivisionCell Division
All cells are derived fromAll cells are derived from pre-pre-
existingexisting cellscells
New cells are produced forNew cells are produced for
growthgrowth and to replaceand to replace damaged ordamaged or
old cellsold cells
Differs inDiffers in prokaryotesprokaryotes (bacteria)(bacteria)
andand eukaryoteseukaryotes (protists, fungi,(protists, fungi,
plants, & animals)plants, & animals)
3. 3
Keeping Cells IdenticalKeeping Cells Identical
TheThe instructions forinstructions for
making cell partsmaking cell parts
are encoded in theare encoded in the
DNADNA, so each new, so each new
cell must get acell must get a
complete set of thecomplete set of the
DNA moleculesDNA molecules
4. 4
DNA ReplicationDNA Replication
DNA must beDNA must be
copied orcopied or
replicatedreplicated
before cellbefore cell
divisiondivision
Each new cellEach new cell
will then have anwill then have an
identical copyidentical copy ofof
the DNAthe DNA
Original DNAOriginal DNA
strandstrand
Two new,Two new,
identical DNAidentical DNA
strandsstrands
7. 7
Prokaryotic ChromosomeProkaryotic Chromosome
The DNA ofThe DNA of
prokaryotesprokaryotes
(bacteria) is(bacteria) is one,one,
circularcircular
chromosomechromosome
attached to theattached to the
inside of the cellinside of the cell
membranemembrane
8. 8
Eukaryotic ChromosomesEukaryotic Chromosomes
AllAll eukaryoticeukaryotic cells store geneticcells store genetic
information in chromosomesinformation in chromosomes
Most eukaryotes have betweenMost eukaryotes have between 10 and10 and
50 chromosomes50 chromosomes in their body cellsin their body cells
Human body cellsHuman body cells havehave 4646 chromosomeschromosomes
or 23 identical pairsor 23 identical pairs
9. 9
Eukaryotic ChromosomesEukaryotic Chromosomes
Each chromosome is composed of aEach chromosome is composed of a
single,single, tightly coiled DNAtightly coiled DNA moleculemolecule
ChromosomesChromosomes can’t be seencan’t be seen whenwhen
cellscells aren’t dividingaren’t dividing and are calledand are called
chromatinchromatin
11. 11
Chromosomes in Dividing CellsChromosomes in Dividing Cells
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister ChromatidsCalled Sister Chromatids
12. 12
KaryotypeKaryotype
AA picturepicture of theof the
chromosomes from achromosomes from a
human cellhuman cell arrangedarranged
in pairs by sizein pairs by size
First 22 pairs areFirst 22 pairs are
calledcalled autosomesautosomes
Last pair are theLast pair are the
sex chromosomessex chromosomes
XXXX female orfemale or XYXY
malemale
13. 13
Boy or Girl?Boy or Girl?
Y - ChromosomeY - Chromosome
X - ChromosomeX - Chromosome
The Y Chromosome DecidesThe Y Chromosome Decides
15. 15
Types of Cell ReproductionTypes of Cell Reproduction
Asexual reproductionAsexual reproduction involves ainvolves a
single cellsingle cell dividing to makedividing to make 2 new,2 new,
identical daughter cellsidentical daughter cells
Mitosis & binary fissionMitosis & binary fission areare
examples of asexual reproductionexamples of asexual reproduction
Sexual reproductionSexual reproduction involves twoinvolves two
cells (egg & sperm) joining to make acells (egg & sperm) joining to make a
new cell (zygote)new cell (zygote) that isthat is NOTNOT
identical to the original cellsidentical to the original cells
MeiosisMeiosis is an exampleis an example
17. 17
Cell Division in ProkaryotesCell Division in Prokaryotes
Prokaryotes such asProkaryotes such as
bacteriabacteria divide into 2divide into 2
identical cells by theidentical cells by the
process ofprocess of binarybinary
fissionfission
Single chromosomeSingle chromosome
makes a copy ofmakes a copy of
itselfitself
Cell wall formsCell wall forms
between thebetween the
chromosomes dividingchromosomes dividing
the cellthe cell
ParentParent
cellcell
2 identical daughter cells2 identical daughter cells
ChromosomeChromosome
doublesdoubles
Cell splitsCell splits
23. 23
Interphase - GInterphase - G11 StageStage
11stst
growth stagegrowth stage after cellafter cell
divisiondivision
CellsCells maturemature by making moreby making more
cytoplasm & organellescytoplasm & organelles
Cell carries on itsCell carries on its normalnormal
metabolic activitiesmetabolic activities
24. 24
Interphase – S StageInterphase – S Stage
SynthesisSynthesis stagestage
DNADNA is copied oris copied or replicatedreplicated
TwoTwo
identicalidentical
copiescopies
of DNAof DNA
OriginalOriginal
DNADNA
25. 25
Interphase – GInterphase – G22 StageStage
22ndnd
GrowthGrowth StageStage
OccursOccurs after DNA has been copiedafter DNA has been copied
All cellAll cell structures needed forstructures needed for
divisiondivision are made (e.g. centrioles)are made (e.g. centrioles)
BothBoth organelles & proteinsorganelles & proteins areare
synthesizedsynthesized
26. 26
What’s Happening in Interphase?What’s Happening in Interphase?
What the cell looks likeWhat the cell looks like
Animal Cell
What’s occurring
27. 27
Sketch the Cell CycleSketch the Cell Cycle
DaughterDaughter
CellsCells
DNA CopiedDNA Copied
CellsCells
MatureMature
Cells prepare forCells prepare for
DivisionDivision
Cell Divides intoCell Divides into
Identical cellsIdentical cells
29. 29
MitosisMitosis
Division of theDivision of the
nucleusnucleus
Also calledAlso called
karyokinesiskaryokinesis
Only occurs inOnly occurs in
eukaryoteseukaryotes
HasHas fourfour stagesstages
Doesn’t occur inDoesn’t occur in
some cells suchsome cells such
asas brain cellsbrain cells
31. 31
Early ProphaseEarly Prophase
ChromatinChromatin in nucleus condenses toin nucleus condenses to
formform visible chromosomesvisible chromosomes
Mitotic spindleMitotic spindle forms from fibers informs from fibers in
cytoskeleton orcytoskeleton or centrioles (animal)centrioles (animal)
ChromosomesChromosomes
NucleolusNucleolus CytoplasmCytoplasm
Nuclear MembraneNuclear Membrane
32. 32
Late ProphaseLate Prophase
Nuclear membrane & nucleolusNuclear membrane & nucleolus areare
broken downbroken down
ChromosomesChromosomes continue condensing &continue condensing &
areare clearly visibleclearly visible
Spindle fibers calledSpindle fibers called kinetochoreskinetochores
attach to the centromereattach to the centromere of eachof each
chromosomechromosome
SpindleSpindle finishes forming between thefinishes forming between the
poles of the cellpoles of the cell
35. 35
Review of ProphaseReview of Prophase
What the cellWhat the cell
looks likelooks like
What’s happeningWhat’s happening
36. 36
Spindle FibersSpindle Fibers
The mitoticThe mitotic spindlespindle form from theform from the
microtubulesmicrotubules in plantsin plants andand centriolescentrioles
in animal cellsin animal cells
Polar fibersPolar fibers extend from one pole ofextend from one pole of
the cell to the opposite polethe cell to the opposite pole
Kinetochore fibersKinetochore fibers extend from theextend from the
pole to the centromere of thepole to the centromere of the
chromosome to which they attachchromosome to which they attach
AstersAsters are short fibers radiatingare short fibers radiating
from centriolesfrom centrioles
38. 38
MetaphaseMetaphase
Chromosomes, attached to theChromosomes, 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 theChromosomes are now lined up at the
equatorequator
Pole ofPole of
the Cellthe Cell
Equator of CellEquator of Cell
45. 45
TelophaseTelophase
Sister chromatids atSister chromatids at oppositeopposite
polespoles
SpindleSpindle disassemblesdisassembles
Nuclear envelopeNuclear envelope forms aroundforms around
each set of sister chromatidseach set of sister chromatids
NucleolusNucleolus reappearsreappears
CYTOKINESISCYTOKINESIS occursoccurs
Chromosomes reappear asChromosomes reappear as
chromatinchromatin
47. 47
CytokinesisCytokinesis
Means division of the cytoplasmMeans division of the cytoplasm
DivisionDivision of cell into two,of cell into two,
identical halves calledidentical halves called daughterdaughter
cellscells
In plant cells, cell plateIn plant cells, cell plate formsforms
at the equator to divide cellat the equator to divide cell
In animal cells,In animal cells, cleavage furrowcleavage furrow
forms to split cellforms to split cell
50. 50
Daughter Cells of MitosisDaughter Cells of Mitosis
Have theHave the same number ofsame number of
chromosomes as each otherchromosomes as each other and asand as
the parent cellthe parent cell from which theyfrom which they
were formedwere formed
IdenticalIdentical to each other, butto each other, but smallersmaller
than parent cellthan parent cell
MustMust grow in sizegrow in size to become matureto become mature
cellscells (G(G11 of Interphase)of Interphase)
51. 51
Identical Daughter CellsIdentical Daughter Cells
Chromosome number theChromosome number the samesame, but cells, but cells
smallersmaller than parent cellthan parent cell
What isWhat is
the 2nthe 2n
oror
diploiddiploid
number?number?
22
56. 56
Eukaryotic Cell DivisionEukaryotic Cell Division
Used forUsed for growth andgrowth and
repairrepair
Produce two new cellsProduce two new cells
identical to the originalidentical to the original
cellcell
Cells areCells are diploid (2n)diploid (2n)
Chromosomes duringChromosomes during
Metaphase of mitosisMetaphase of mitosis
ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase
TelophaseTelophase
CytokinesisCytokinesis
62. 62
Name the Stages of Mitosis:Name the Stages of Mitosis:
Interphase
Early prophase
Mid-Prophase
Late
Prophase
Metaphase
Late
Anaphase
Early Anaphase
Early
Telophase,
Begin
cytokinesis
Late telophase,
Advanced
cytokinesis
63. 63
Identify the StagesIdentify the Stages
Early, Middle, & Late ProphaseEarly, Middle, & Late Prophase
Late ProphaseLate Prophase MetaphaseMetaphase AnaphaseAnaphase
Late AnaphaseLate Anaphase TelophaseTelophase Telophase &Telophase &
CytokinesisCytokinesis
??
?? ?? ??
?? ?? ??
64. 64
Locate the Four MitoticLocate the Four Mitotic
Stages in PlantsStages in Plants
MetaphaseMetaphase
ProphaseProphase
AnaphaseAnaphase
TelophaseTelophase
65. 65
Uncontrolled Mitosis
If mitosis is notIf mitosis is not
controlledcontrolled, unlimited, unlimited
cell division occurscell division occurs
causing cancerouscausing cancerous
tumorstumors
OncogenesOncogenes are specialare special
proteinsproteins that
increase the chanceincrease the chance
that a normal cellthat a normal cell
develops into adevelops into a tumortumor
cellcell
Cancer cellsCancer cells
67. 67
Facts About MeiosisFacts About Meiosis
Preceded by interphase whichPreceded by interphase which
includesincludes chromosome replicationchromosome replication
TwoTwo meiotic divisions ---meiotic divisions --- MeiosisMeiosis
I and Meiosis III and Meiosis II
Called Reduction- divisionCalled Reduction- division
Original cell is diploid (2n)Original cell is diploid (2n)
Four daughter cellsFour daughter cells produced thatproduced that
areare monoploid (1n)monoploid (1n)
68. 68
Facts About MeiosisFacts About Meiosis
Daughter cellsDaughter cells contain half thecontain half the
number of chromosomesnumber of chromosomes as theas the
original celloriginal cell
ProducesProduces gametesgametes (eggs & sperm(eggs & sperm))
Occurs in theOccurs in the testestestes in malesin males
((SpermatogenesisSpermatogenesis))
Occurs in theOccurs in the ovariesovaries in femalesin females
((OogenesisOogenesis))
70. 70
Why Do we Need Meiosis?Why Do we Need Meiosis?
It is the fundamental basis ofIt is the fundamental basis of
sexual reproductionsexual reproduction
Two haploid (1n) gametes areTwo haploid (1n) gametes are
brought together throughbrought together through
fertilizationfertilization to form a diploidto form a diploid
(2n) zygote(2n) zygote
71. 71
Fertilization – “Putting itFertilization – “Putting it
all together”all together”
1n =31n =3
2n = 62n = 6
72. 72
Replication of ChromosomesReplication of Chromosomes
ReplicationReplication is theis the
process ofprocess of
duplicating aduplicating a
chromosomechromosome
OccursOccurs prior toprior to
divisiondivision
Replicated copiesReplicated copies
are calledare called sistersister
chromatidschromatids
Held together atHeld together at
centromerecentromere
Occurs inOccurs in
InterphaseInterphase
73. 73
A Replicated ChromosomeA Replicated Chromosome
HomologsHomologs
(same genes,(same genes,
different alleles)different alleles)
SisterSister
ChromatidsChromatids
(same genes,(same genes,
same alleles)same alleles)
Gene XGene X
Homologs separate in meiosis I andHomologs separate in meiosis I and
therefore different alleles separate.therefore different alleles separate.
74. 74
Meiosis Forms Haploid GametesMeiosis Forms Haploid Gametes
Meiosis mustMeiosis must reduce the chromosome numberreduce the chromosome number
by halfby half
Fertilization then restoresFertilization then restores the 2n numberthe 2n number
from mom from dad child
meiosis reduces
genetic content
too
much!
The right
number!
75. 75
Meiosis: Two Part CellMeiosis: Two Part Cell
DivisionDivision
HomologsHomologs
separateseparate
SisterSister
chromatidschromatids
separateseparate
DiploidDiploid
MeiosisMeiosis
II
MeiosisMeiosis
IIII
DiploidDiploid
HaploidHaploid
76. 76
Meiosis I: Reduction DivisionMeiosis I: Reduction Division
NucleusNucleus SpindleSpindle
fibersfibers NuclearNuclear
envelopeenvelopeEarlyEarly
Prophase IProphase I
(Chromosome(Chromosome
numbernumber
doubleddoubled))
LateLate
ProphaseProphase
II
MetaphaseMetaphase
II AnaphaseAnaphase
II
Telophase ITelophase I
(diploid)(diploid)
77. 77
Prophase IProphase I
Early prophaseEarly prophase
Homologs pair.Homologs pair.
Crossing overCrossing over
occursoccurs.
Late prophaseLate prophase
Chromosomes condense.Chromosomes condense.
Spindle forms.Spindle forms.
Nuclear envelopeNuclear envelope
fragments.fragments.
78. 78
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
81. 81
Crossing-over multiplies the already hugeCrossing-over multiplies the already huge
number of different gamete typesnumber of different gamete types
produced by independent assortmentproduced by independent assortment
Crossing-OverCrossing-Over
82. 82
Metaphase IMetaphase I
Homologous pairsHomologous pairs
of chromosomesof chromosomes
align along thealign along the
equatorequator of theof the
cellcell
83. 83
Anaphase IAnaphase I
Homologs separateHomologs separate andand
move to opposite poles.move to opposite poles.
Sister chromatidsSister chromatids remainremain
attachedattached at theirat their
centromerescentromeres.
84. 84
Telophase ITelophase I
Nuclear envelopesNuclear envelopes
reassemble.reassemble.
Spindle disappears.Spindle disappears.
CytokinesisCytokinesis divides celldivides cell
into two.into two.
85. 85
Meiosis IIMeiosis II
Only one homolog of eachOnly one homolog of each
chromosome is present inchromosome is present in
the cellthe cell.
Meiosis II produces gametes withMeiosis II produces gametes with
one copy of each chromosome andone copy of each chromosome and
thus one copy of each gene.thus one copy of each gene.
Sister chromatids carrySister chromatids carry
identical geneticidentical genetic
informationinformation..
Gene XGene X
89. 89
Anaphase IIAnaphase II
Sister chromatidsSister chromatids
separate andseparate and
move tomove to oppositeopposite
polespoles.
EquatorEquator
PolePole
90. 90
Telophase IITelophase II
Nuclear envelopeNuclear envelope
assembles.assembles.
ChromosomesChromosomes
decondense.decondense.
Spindle disappears.Spindle disappears.
Cytokinesis dividesCytokinesis divides
cell into two.cell into two.
91. 91
Results of MeiosisResults of Meiosis
Gametes (egg & sperm)Gametes (egg & sperm)
formform
Four haploid cells withFour haploid cells with
one copy of eachone copy of each
chromosomechromosome
One allele of each geneOne allele of each gene
Different combinations ofDifferent combinations of
alleles for differentalleles for different
genes along thegenes along the
chromosomechromosome
93. 93
SpermatogenesisSpermatogenesis
Occurs in theOccurs in the
testestestes
Two divisionsTwo divisions
produce 4produce 4
spermatidsspermatids
SpermatidsSpermatids maturemature
into sperminto sperm
Men produce aboutMen produce about
250,000,000250,000,000
sperm per daysperm per day
96. 96
OogenesisOogenesis
Occurs in theOccurs in the ovariesovaries
Two divisions produceTwo divisions produce 3 polar bodies3 polar bodies
that die andthat die and 1 egg1 egg
Polar bodies die because ofPolar bodies die because of unequalunequal
division of cytoplasmdivision of cytoplasm
Immature egg calledImmature egg called oocyteoocyte
Starting at puberty, one oocyteStarting at puberty, one oocyte
matures into anmatures into an ovum (egg)ovum (egg) every 28every 28
daysdays
100. 100
MitosisMitosis MeiosisMeiosis
Number ofNumber of
divisionsdivisions
11
22
Number ofNumber of
daughter cellsdaughter cells
22 44
GeneticallyGenetically
identical?identical?
YesYes NoNo
Chromosome #Chromosome # Same as parentSame as parent Half of parentHalf of parent
WhereWhere Somatic cellsSomatic cells Germ cellsGerm cells
WhenWhen Throughout lifeThroughout life At sexual maturityAt sexual maturity
RoleRole Growth andGrowth and
repairrepair
Sexual reproductionSexual reproduction
Comparison of DivisionsComparison of Divisions
Replication is the process of duplicating chromosome. The new copy of a chromosome is formed by DNA synthesis during S-phase. The chromosome copies are called sister chromatids. Sister chromatids are held together at the centromere.
