Cellular Reproduction Cellular Reproduction Cell Division Cell Division cellular material is cellular material is divided between divided between new daughter cells new daughter cells Nuclear division: Mitosis Nuclear division: Mitosis or Meiosis or Meiosis Cytoplasmic division: Cytoplasmic division: Cytokinesis Cytokinesis
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Cellular Reproduction Cell Division cellular material is divided between new daughter cells cellular material is divided between new daughter cells Nuclear.
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Cellular ReproductionCellular Reproduction
Cell DivisionCell Division cellular material is divided between cellular material is divided between new daughter cells new daughter cells
Nuclear division: Mitosis or MeiosisNuclear division: Mitosis or Meiosis
Each chromosome appears as a pair of Each chromosome appears as a pair of chromatids attached at the centromere. chromatids attached at the centromere.
chromatid chromatid
centromere centromere
Sister Sister Chromatids are Chromatids are held together held together at their at their centromeres. centromeres.
chromatid chromatid
Chromatid pairs align Chromatid pairs align at the cell equator.at the cell equator.
MetaphaseMetaphase
Sister chromatids separate Sister chromatids separate
and are drawn to opposite and are drawn to opposite poles by spindle fibers.poles by spindle fibers.
AnaphaseAnaphase
Chromosomes have reached poles of cell. Chromosomes have reached poles of cell. Spindle disperses.Spindle disperses.Nuclear envelope surrounds chromosomes. Nuclear envelope surrounds chromosomes. Chromosomes become diffuse, nucleolus reforms.Chromosomes become diffuse, nucleolus reforms.
TelophaseTelophase
Telophase +Telophase +CytokinesisCytokinesis
These phases can overlap in time.These phases can overlap in time.
New Daughter CellsNew Daughter Cells
Cytokinesis in animal cellsCytokinesis in animal cells
Cytokinesis in plant cellsCytokinesis in plant cells
Applying Your KnowledgeApplying Your Knowledge
A.A. When do chromosomes line up at the When do chromosomes line up at the cell equator? cell equator?
B.B. When are sister chromatids first visible? When are sister chromatids first visible?
C.C. When do sister chromatids separate When do sister chromatids separate from each other? from each other?
• Diploid cells have Diploid cells have pairs of pairs of chromosomeschromosomes
• Each homologous Each homologous chromosome pair chromosome pair is genetically is genetically matched so that matched so that the genes are the genes are arranged in the arranged in the same order same order
Cell Cycle With Meiosis Cell Cycle With Meiosis
G1S
G2
cytoplasm doubles
chromosomesreplicate
assembly of components for division cytokinesis
M1
MeiosisMeiosisMeiosis
M1 = meiosis IM1 = meiosis I M2 = meiosis IIM2 = meiosis II
Separation of homologous chromosomes Separation of homologous chromosomes into two different nucleiinto two different nucleiChromosome number reduced to haploidChromosome number reduced to haploid
Meiosis II: equational divisionMeiosis II: equational divisionDuplicated chromosomes separateDuplicated chromosomes separateNo change in chromosome numberNo change in chromosome number
Phases of Meiosis I Phases of Meiosis I
Prophase IProphase I --Chromosomes Shorten and --Chromosomes Shorten and Thicken (condense) Thicken (condense)--Homologous Chromosomes --Homologous Chromosomes Pair with Each Other and Pair with Each Other and Exchange Genetic Information Exchange Genetic Information
Metaphase IMetaphase I Chromosome Pairs Line up at Chromosome Pairs Line up at Cell EquatorCell Equator
Anaphase IAnaphase I Homologous Chromosomes Homologous Chromosomes SeparateSeparate
Telophase ITelophase I Separated Homologues Reach Separated Homologues Reach Opposite Poles Opposite Poles
Chromosomes condense.Chromosomes condense.Synapsis (pairing) of homologs occurs. Synapsis (pairing) of homologs occurs. Crossing-over occurs at chiasma (contact points).Crossing-over occurs at chiasma (contact points).
Prior to the start of Prior to the start of Meiosis II, there may be Meiosis II, there may be a pause called a pause called interkinesis but the interkinesis but the chromosomes do not chromosomes do not duplicate a second time. duplicate a second time.
Cytokinesis along the Cytokinesis along the central plane yields two central plane yields two haploid cells with haploid cells with duplicated duplicated chromosomes. chromosomes.
Phases of Meiosis II Phases of Meiosis II
Prophase IIProphase II --Chromosomes Shorten and --Chromosomes Shorten and Thicken (condense) Thicken (condense)
After cytokinesis, After cytokinesis, four genetically-different four genetically-different haploid cells are formed. haploid cells are formed.
Sperm formationSperm formation
•Equal divisions ofEqual divisions of cytoplasm cytoplasm•Four functional Four functional products per meiosis products per meiosis
Egg formationEgg formation
•Unequal divisions of Unequal divisions of cytoplasm cytoplasm•Small polar bodies formedSmall polar bodies formed•One functional product per One functional product per
meiosis meiosis
Applying Your KnowledgeApplying Your Knowledge
A.A. When do sister chromatids separate?When do sister chromatids separate?
B.B. When does crossing over occur?When does crossing over occur?
C.C. When do homologous pairs line up at When do homologous pairs line up at the cell equator?the cell equator?
1.1. Prophase IProphase I
2.2. Metaphase IMetaphase I
3.3. Anaphase IAnaphase I
4.4. Metaphase IIMetaphase II
5.5. Anaphase IIAnaphase II
Comparing Mitosis and MeiosisComparing Mitosis and Meiosis
MitosisMitosis MeiosisMeiosisCell type at start Cell type at start
Cell type at endCell type at end
Are products identical? (Y/N)Are products identical? (Y/N)
Number of cells producedNumber of cells produced
Number of chromosome Number of chromosome duplicationsduplications
Pairing of homologues (Y/N)Pairing of homologues (Y/N)
Crossing-over (Y/N)Crossing-over (Y/N)
Number of chromosome Number of chromosome divisionsdivisions
Comparing Mitosis and MeiosisComparing Mitosis and Meiosis
MitosisMitosis MeiosisMeiosisCell type at start Cell type at start DiploidDiploid DiploidDiploidCell type at endCell type at end DiploidDiploid HaploidHaploidAre products identical? (Y/N)Are products identical? (Y/N) YesYes NoNoNumber of cells producedNumber of cells produced TwoTwo FourFourNumber of chromosome Number of chromosome duplications prior toduplications prior to
OneOne OneOne
Pairing of homologues (Y/N)Pairing of homologues (Y/N) NoNo YesYesCrossing-over (Y/N)Crossing-over (Y/N) NoNo YesYesNumber of chromosome Number of chromosome divisionsdivisions