•mitosis meiosis •identical daughter cells •clones · preparing for meiosis •preceded by...
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MeiosisMeiosisMeiosisMeiosis& Sexual Reproduction
Cell Division –Asexual reproduction
• Mitosis
– produce cells with same information• identical daughter cells
– exact copies•clones
– same amount of DNA •same number of chromosomes
• same genetic information
Asexual reproduction
• Single-celled eukaryotes and simple multicellular eukaryotes reproduce asexually
Binary fission in AmoebaBinary fission in AmoebaBinary fission in AmoebaBinary fission in Amoeba
Budding in YeastBudding in YeastBudding in YeastBudding in Yeast Budding in Budding in Budding in Budding in HydraHydraHydraHydra
How about the rest of us?
• What if a complex multicellular organism (like us) wants to reproduce?
– joining of egg + sperm
• Do we make egg & sperm by mitosis?
46464646 46464646++++ 92929292
eggeggeggegg spermspermspermsperm zygotezygotezygotezygote
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How do we make sperm & eggs?
• reduce 46 chromosomes → 23 chromosomes– half the number of chromosomes
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eggeggeggegg
spermspermspermsperm
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meiosismeiosismeiosismeiosis 46464646
fertilizationfertilizationfertilizationfertilization
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Review: MitosisReview: MitosisReview: MitosisReview: Mitosis• Division Division Division Division of theof theof theof the NUCLEUSNUCLEUSNUCLEUSNUCLEUS
• Purpose: growth & repairPurpose: growth & repairPurpose: growth & repairPurpose: growth & repair
• Four StagesFour StagesFour StagesFour Stages
• Can you identify them?Can you identify them?Can you identify them?Can you identify them?
Four Mitotic StagesFour Mitotic StagesFour Mitotic StagesFour Mitotic Stages
•ProProProProphasephasephasephase
•MetaMetaMetaMetaphasephasephasephase
•AnaAnaAnaAnaphasephasephasephase
•TeloTeloTeloTelophasephasephasephase
MitosisMitosisMitosisMitosis
• Produces two new cellsidentical to the original cell
• Cells are diploid (2n)
Chromosomes during Chromosomes during Chromosomes during Chromosomes during Metaphase of mitosisMetaphase of mitosisMetaphase of mitosisMetaphase of mitosis
ProphaseProphaseProphaseProphase MetaphaseMetaphaseMetaphaseMetaphase AnaphaseAnaphaseAnaphaseAnaphase TelophaseTelophaseTelophaseTelophaseCytokinesisCytokinesisCytokinesisCytokinesis
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Facts About MeiosisFacts About MeiosisFacts About MeiosisFacts About MeiosisFacts About MeiosisFacts About MeiosisFacts About MeiosisFacts About Meiosis•• Preceded by interphase which includes Preceded by interphase which includes chromosome replicationchromosome replication
•• TwoTwo meiotic divisions meiotic divisions ------
Meiosis I and Meiosis IIMeiosis I and Meiosis II
•• Called Called reductionreduction--divisiondivision
•• Original cell is diploid (2n)Original cell is diploid (2n)
•• Four daughter cells produced that are Four daughter cells produced that are haploid (1n)haploid (1n)
Facts About MeiosisFacts About MeiosisFacts About MeiosisFacts About Meiosis
•Produces gametes (eggs & sperm)Produces gametes (eggs & sperm)Produces gametes (eggs & sperm)Produces gametes (eggs & sperm)
•Occurs in theOccurs in theOccurs in theOccurs in the testes testes testes testes in malesin malesin malesin males
= = = = SpermatogenesisSpermatogenesisSpermatogenesisSpermatogenesis
• Occurs in theOccurs in theOccurs in theOccurs in the ovaries ovaries ovaries ovaries in femalesin femalesin femalesin females
= = = = OogenesisOogenesisOogenesisOogenesis
---- 2 copies2 copies2 copies2 copies
---- diploiddiploiddiploiddiploid
---- 2n2n2n2n
---- 1 copy1 copy1 copy1 copy
---- haploidhaploidhaploidhaploid
---- 1n1n1n1n
Meiosis = reduction divisionMeiosis = reduction divisionMeiosis = reduction divisionMeiosis = reduction division Homologous chromosomes• Paired chromosomes – one from each parent
– both chromosomes of a pair carry genes
• control same inherited characters
• homologous = same information
diploiddiploiddiploiddiploid2n2n2n2n
homologoushomologoushomologoushomologouschromosomeschromosomeschromosomeschromosomes
Replicated Replicated Replicated Replicated homologous chromosomeshomologous chromosomeshomologous chromosomeshomologous chromosomes
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2n = 2n = 2n = 2n = 6666doubledoubledoubledoublestrandedstrandedstrandedstranded
2n = 2n = 2n = 2n = 6666singlesinglesinglesingle
strandedstrandedstrandedstranded
Preparing for meiosis
• Preceded by Interphase
– Duplication of DNA
– S phase of interphaseof MEIOSIS(just like in mitosis)
M1 prophaseM1 prophaseM1 prophaseM1 prophase
Meiosis: Two Part Cell DivisionMeiosis: Two Part Cell Division
HomologsHomologsHomologsHomologsseparateseparateseparateseparate
Sister Sister Sister Sister chromatidschromatidschromatidschromatidsseparateseparateseparateseparate
Meiosis I
DiploidDiploidDiploidDiploid
HaploidHaploidHaploidHaploid
Meiosis II
HaploidHaploidHaploidHaploid
Homologous ChromosomesHomologous ChromosomesHomologous ChromosomesHomologous ChromosomesHomologous ChromosomesHomologous ChromosomesHomologous ChromosomesHomologous Chromosomesseparate in meiosis Iseparate in meiosis Iseparate in meiosis Iseparate in meiosis Iseparate in meiosis Iseparate in meiosis Iseparate in meiosis Iseparate in meiosis I
SisterSisterSisterSisterSisterSisterSisterSisterChromatidsChromatidsChromatidsChromatidsChromatidsChromatidsChromatidsChromatidssame genes,same genes,same genes,same genes,same genes,same genes,same genes,same genes,same allelessame allelessame allelessame allelessame allelessame allelessame allelessame alleles
HomologsHomologsHomologsHomologsHomologsHomologsHomologsHomologssame genes,same genes,same genes,same genes,same genes,same genes,same genes,same genes,different allelesdifferent allelesdifferent allelesdifferent allelesdifferent allelesdifferent allelesdifferent allelesdifferent alleles
Meiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction DivisionMeiosis I: Reduction Division
NucleusNucleusNucleusNucleusNucleusNucleusNucleusNucleus SpindleSpindleSpindleSpindleSpindleSpindleSpindleSpindlefibersfibersfibersfibersfibersfibersfibersfibers NuclearNuclearNuclearNuclearNuclearNuclearNuclearNuclear
envelopeenvelopeenvelopeenvelopeenvelopeenvelopeenvelopeenvelopeEarly Prophase IEarly Prophase IEarly Prophase IEarly Prophase IEarly Prophase IEarly Prophase IEarly Prophase IEarly Prophase I(Chromosome (Chromosome (Chromosome (Chromosome (Chromosome (Chromosome (Chromosome (Chromosome
number doubled)number doubled)number doubled)number doubled)number doubled)number doubled)number doubled)number doubled)
Late Late Late Late Late Late Late Late Prophase IProphase IProphase IProphase IProphase IProphase IProphase IProphase I
Metaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase I
Telophase ITelophase ITelophase ITelophase ITelophase ITelophase ITelophase ITelophase I
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Prophase IProphase IProphase IProphase I
Early prophaseEarly prophaseEarly prophaseEarly prophaseLate prophaseLate prophaseLate prophaseLate prophase
•HomologsHomologsHomologsHomologs pairpairpairpair
•Crossing over occursCrossing over occursCrossing over occursCrossing over occurs
•Chromosomes condenseChromosomes condenseChromosomes condenseChromosomes condense
•Spindle formsSpindle formsSpindle formsSpindle forms
•Nuclear envelope fragmentsNuclear envelope fragmentsNuclear envelope fragmentsNuclear envelope fragments
Tetrads Form in Prophase ITetrads Form in Prophase ITetrads Form in Prophase ITetrads Form in Prophase IHomologous chromosomesHomologous chromosomesHomologous chromosomesHomologous chromosomes
(each with sister chromatids) (each with sister chromatids) (each with sister chromatids) (each with sister chromatids) Join to form aJoin to form aJoin to form aJoin to form a
TETRADTETRADTETRADTETRAD
Called SynapsisCalled SynapsisCalled SynapsisCalled Synapsis
Crossing over- homologous pairs swappieces of chromosome
- Creates new combinations of traits
tetradtetradtetradtetrad
synapsissynapsissynapsissynapsisfrom mom
from dad
Sister chromatids homologs
from mom
from dad
Sister chromatids homologs
Metaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase IMetaphase I
Homologous pairsHomologous pairsHomologous pairsHomologous pairsof chromosomes of chromosomes of chromosomes of chromosomes align along the align along the align along the align along the
equator of the cellequator of the cellequator of the cellequator of the cell
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Independent Assortment
- chromosomes line up randomly
- independent of one another
- How many possibilities???
- 2n (n=number of chromosomes)
Independent Assortment
- in humans produces 223 (8,388,608)different combinations
Before meiosis
After meiosis
Maternal
Paternal
Anaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase IAnaphase I
Homologs separateHomologs separateHomologs separateHomologs separateHomologs separateHomologs separateHomologs separateHomologs separate and and and and and and and and move to opposite poles.move to opposite poles.move to opposite poles.move to opposite poles.move to opposite poles.move to opposite poles.move to opposite poles.move to opposite poles.
Sister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatids remain remain remain remain remain remain remain remain attachedattachedattachedattachedattachedattachedattachedattached at theirat theirat theirat theirat theirat theirat theirat theircentromerescentromerescentromerescentromerescentromerescentromerescentromerescentromeres.
Telophase ITelophase ITelophase ITelophase ITelophase ITelophase ITelophase ITelophase I
Nuclear envelopesNuclear envelopesNuclear envelopesNuclear envelopesNuclear envelopesNuclear envelopesNuclear envelopesNuclear envelopes reassemblereassemblereassemblereassemblereassemblereassemblereassemblereassemble
Spindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappears
CytokinesisCytokinesisCytokinesisCytokinesisCytokinesisCytokinesisCytokinesisCytokinesis divides cell into two.divides cell into two.divides cell into two.divides cell into two.divides cell into two.divides cell into two.divides cell into two.divides cell into two.
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2n = 2n = 2n = 2n = 4444doubledoubledoubledoublestrandedstrandedstrandedstranded
2n = 2n = 2n = 2n = 4444singlesinglesinglesingle
strandedstrandedstrandedstranded
Review: Meiosis I
prophase1prophase1prophase1prophase1
2n = 2n = 2n = 2n = 4444doubledoubledoubledoublestrandedstrandedstrandedstranded
• 1st division of meiosis separateshomologous pairs
1n1n1n1n = = = = 2222doubledoubledoubledoublestrandedstrandedstrandedstranded
tetrad
synapsis
telophase1telophase1telophase1telophase1
metaphase1metaphase1metaphase1metaphase1
Meiosis 2
1n1n1n1n = = = = 2222doubledoubledoubledoublestrandedstrandedstrandedstranded
1n1n1n1n = = = = 2222singlesinglesinglesingle
strandedstrandedstrandedstranded
metaphase2metaphase2metaphase2metaphase2
telophase2telophase2telophase2telophase2
prophase2prophase2prophase2prophase2
1n1n1n1n = = = = 2222doubledoubledoubledoublestrandedstrandedstrandedstranded
• 2nd division of meiosis separatessister chromatids
Meiosis IIMeiosis IIMeiosis IIMeiosis IIMeiosis IIMeiosis IIMeiosis IIMeiosis II
Only one homolog of each Only one homolog of each Only one homolog of each Only one homolog of each Only one homolog of each Only one homolog of each Only one homolog of each Only one homolog of each chromosome is present in the cellchromosome is present in the cellchromosome is present in the cellchromosome is present in the cellchromosome is present in the cellchromosome is present in the cellchromosome is present in the cellchromosome is present in the cell.
Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with Meiosis II produces gametes with
one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each chromosome and thus one copy of each gene.one copy of each gene.one copy of each gene.one copy of each gene.one copy of each gene.one copy of each gene.one copy of each gene.one copy of each gene.
Sister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsare still attachedare still attachedare still attachedare still attachedare still attachedare still attachedare still attachedare still attached
Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome Meiosis II: Reducing Chromosome NumberNumberNumberNumberNumberNumberNumberNumber
Prophase IIProphase IIProphase IIProphase IIProphase IIProphase IIProphase IIProphase II Metaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase II
Anaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IITelophase IITelophase IITelophase IITelophase IITelophase IITelophase IITelophase IITelophase II
4 haploid cells4 haploid cells4 haploid cells4 haploid cells4 haploid cells4 haploid cells4 haploid cells4 haploid cells
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Prophase IIProphase IIProphase IIProphase IIProphase IIProphase IIProphase IIProphase II
Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope fragments.fragments.fragments.fragments.fragments.fragments.fragments.fragments.
Spindle forms.Spindle forms.Spindle forms.Spindle forms.Spindle forms.Spindle forms.Spindle forms.Spindle forms.
Metaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase IIMetaphase II
Chromosomes align Chromosomes align Chromosomes align Chromosomes align Chromosomes align Chromosomes align Chromosomes align Chromosomes align along equator of cellalong equator of cellalong equator of cellalong equator of cellalong equator of cellalong equator of cellalong equator of cellalong equator of cell........
Anaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase IIAnaphase II
Sister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsSister chromatidsseparate and move separate and move separate and move separate and move separate and move separate and move separate and move separate and move to opposite polesto opposite polesto opposite polesto opposite polesto opposite polesto opposite polesto opposite polesto opposite poles.
EquatorEquatorEquatorEquatorEquatorEquatorEquatorEquator
PolePolePolePolePolePolePolePole
Telophase IITelophase IITelophase IITelophase IITelophase IITelophase IITelophase IITelophase II
Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope Nuclear envelope assemblesassemblesassemblesassemblesassemblesassemblesassemblesassembles
Chromosomes Chromosomes Chromosomes Chromosomes Chromosomes Chromosomes Chromosomes Chromosomes decondensedecondensedecondensedecondensedecondensedecondensedecondensedecondense
Spindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappearsSpindle disappears
Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell Cytokinesis divides cell into twointo twointo twointo twointo twointo twointo twointo two
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Results of MeiosisResults of MeiosisResults of MeiosisResults of MeiosisResults of MeiosisResults of MeiosisResults of MeiosisResults of Meiosis
Gametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) formGametes (egg & sperm) form
Four haploid cellsFour haploid cellsFour haploid cellsFour haploid cellsFour haploid cellsFour haploid cellsFour haploid cellsFour haploid cells with one with one with one with one with one with one with one with one copy of each chromosome copy of each chromosome copy of each chromosome copy of each chromosome copy of each chromosome copy of each chromosome copy of each chromosome copy of each chromosome
One allele of each geneOne allele of each geneOne allele of each geneOne allele of each geneOne allele of each geneOne allele of each geneOne allele of each geneOne allele of each gene
Different combinations of Different combinations of Different combinations of Different combinations of Different combinations of Different combinations of Different combinations of Different combinations of alleles for different genes alleles for different genes alleles for different genes alleles for different genes alleles for different genes alleles for different genes alleles for different genes alleles for different genes along the chromosomealong the chromosomealong the chromosomealong the chromosomealong the chromosomealong the chromosomealong the chromosomealong the chromosome
Meiosis 1
Meiosis 2
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The value of meiosis
• Meiosis introduces genetic variation– gametes of offspring do not have same genes as gametes from parents
– This is the raw material for EVOLUTIONEVOLUTIONEVOLUTIONEVOLUTION
from Momfrom Momfrom Momfrom Mom from Dadfrom Dadfrom Dadfrom Dadnew gametesnew gametesnew gametesnew gametes
made by offspringmade by offspringmade by offspringmade by offspring
Sources of genetic variability
• Genetic variability in sexual reproduction
– independent assortment•homologous chromosomes in Meiosis 1
– crossing over•between homologous chromosomes in prophase 1
– random fertilization• random ovum fertilized by a random sperm
Any 2 parents will produce a zygote with over 70 trillion(223 x 223) diploid combinations
Sexual reproduction creates variability
Sexual reproduction allows us to maintain both genetic similarity & differences.
Martin & Charlie Sheen, Emilio EstevezMartin & Charlie Sheen, Emilio EstevezMartin & Charlie Sheen, Emilio EstevezMartin & Charlie Sheen, Emilio Estevez
Michael & KirkMichael & KirkMichael & KirkMichael & KirkDouglasDouglasDouglasDouglas
Baldwin brothersBaldwin brothersBaldwin brothersBaldwin brothers