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    Pmed214 m&m 2012(1) Pmed214 m&m 2012(1) Presentation Transcript

    • Mitosis & MeiosisDr. Jeelan MoghrabyB.Sc., D.PhilAssistant ProfessorEmail: moghrabyj@ksau-hs.edu.saPMED214 2013
    • ObjectivesCell DivisionPhases of the cell cycleMitosisMeiosisDr. J MoghrabyMeiosis
    • Cell DivisionContinuity of life is based on the reproductionof cells
    • Unicellular organisms: division of one cell reproducesthe entire organismMulti-cellular organisms: growth, repair anddevelopment of fertilized cell are dependent on celldivisionDr. J MoghrabydivisionCell division results in genetically identical daughtercells
    • Genetic Material of a Eukaryotic CellDr. J Moghraby© 2008 by Steven M. Carr, after original by GenetixSomatic cells have two setsof chromosomesDNA packaged intochromosomes consistingof chromatin
    • ChromosomesChromosomeduplication(including DNAsynthesis)Chromo-some armDNA moleculesResults in twoidentical copiescalled sisterchromatids that areDuplication of DNADr. J MoghrabySisterchromatidsSeparation ofsister chromatidsCentromereSister chromatidschromatids that areconnected bycentromeres
    • Phases of the Cell CycleDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • SGControlsystemG1 checkpointCell Cycle ControlThree majorcheckpointsG1 checkpoint =‘start’Dr. J MoghrabySG1M checkpointG2MsystemG2 checkpoint‘start’Without correct signalto pass the G1checkpoint, exit thecell cycle and enterthe non-dividing G0phase
    • 2001 Nobel Prizes in Eukaryotic Cell CycleHartwell Nurse HuntDr. J MoghrabyHartwell Nurse HuntCell cycle checkpointsCyclin-dependent kinasesCyclins
    • Most cells result in identical daughter cells (2n) inprocess of mitosis and cytokinesisMeiosis is a special type of division producing non-identical daughter cells (1n)Dr. J Moghrabyidentical daughter cells (1n)Both cell divisions go through interphase
    • Mitotic & Meiotic Cell CyclesMitosisDr. J MoghrabyMeiosis© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • InterphaseDuring all three phases the cell grows and carries outmetabolic activitiesOrganelles are producedDNA is duplicated during S phase only;Dr. J MoghrabyDNA is duplicated during S phase only;chromosomes are dispersed in nucleusLength of phases vary between cells
    • MitosisGeneration of two identical daughter cellsfrom a single cell
    • Mitosis is Divided into Five PhasesProphasePrometaphaseMetaphaseAnaphaseDr. J MoghrabyAnaphaseTelophaseCytokinesis begins during telophase
    • ProphaseChromosomes begin to condenseMitotic spindle of microtubules begins to formNucleoli disappear and nuclear envelope begins tobreak downbreak downDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • PrometaphaseFragmentation of nuclear envelopeMitotic spindle attach to thecondensed chromosomes at theircentromeres via kinetochoresChromosomes have a bi-orientaionDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • MetaphaseKinetochores and spindle fibresalign the chromosomes at themetaphase platemetaphase plateCheckpoint determines whetherspindles are assembled properlyDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • AnaphaseSister chromatids separateKinetochore microtubules shortenpulling the chromosomes topulling the chromosomes toopposite spindle polesDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Telophase & CytokinesisChromosomes reach poles; begin to expandMicrotubules are lostNuclear envelope reformsCytokinesis results in two genetically identicaldaughter cellsdaughter cellsDr. J MoghrabyCleavage furrow100 mDaughter cellsCleavage of an animal cell (SEM)Contractile ring ofmicrofilaments© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • MITOTIC (M) PHASECytokinesisMitosisSG1G2Mitotic DivisionDr. J MoghrabyTelophase &CytokinesisAnaphaseMetaphasePrometaphaseProphase
    • MeiosisGeneration of four, genetically distinct,haploid cells from a single cell
    • Meioun from Greek meaning ‘to make small’Restricted to germ cells in gonadsGametes have a haploid set of 23 chromosomesMale = spermDr. J MoghrabyMale = spermFemale = ova
    • Timing of Meiosis DiffersSpermatogonia enter meiosis at different times (afterpuberty)Oogonia enter meiosis within fetal ovary arresting atmeiosis I prophase; oocytesmeiosis I prophase; oocytesOocytes re-enter meiosis when ovulated in responseto hormonesDr. J Moghraby
    • Meiosis Consists of Two DivisionsMeiosis I: homologous chromosomes separate toproduce two haploid cells; reductional divisionMeiosis II: sister chromatids separate resulting in fourhaploid cells; equational divisionDr. J Moghrabyhaploid cells; equational divisionDNA duplication occurs before meiosis I in interphase
    • Stages of MeiosisInterphaseHomologous pair of chromosomesin diploid parent cellDr. J MoghrabyChromosomesreplicateHomologous pair of replicated chromosomesSisterchromatids Diploid cell withreplicatedchromosomes
    • InterphaseHomologous pair of chromosomesin diploid parent cellChromosomesreplicateHomologous pair of replicated chromosomesDr. J MoghrabySisterchromatids Diploid cell withreplicatedchromosomesMeiosis IHomologouschromosomesseparate1Haploid cells withreplicated chromosomes
    • InterphaseHomologous pair of chromosomesin diploid parent cellChromosomesreplicateHomologous pair of replicated chromosomesSisterchromatids Diploid cell withreplicatedchromosomesDr. J MoghrabychromosomesMeiosis IHomologouschromosomesseparate1Haploid cells withreplicated chromosomesMeiosis II2 Sister chromatidsseparateHaploid cells with unreplicated chromosomes
    • Meiosis IProphase IMetaphase IAnaphase IMeiosis IIProphase IIMetaphase IIAnaphase IIAnaphase ITelophase I &cytokinesisAnaphase IITelophase II &cytokinesisDr. J Moghraby
    • Meiosis IProphase I:– Takes up ~90% of time of meiosis– Chromosomes condense– Formation of tetrad– Crossing over between homologous chromatids in regions– Crossing over between homologous chromatids in regionscalled chiasmataDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Metaphase I:– Pairs of homologous chromosomesline up on metaphase plate oppositeeach other– Kinetochores on sister chromatidsface same poleDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Anaphase I:– Homologous chromosomesmove to opposite poles;sister chromatids stayattachedattachedTelophase I & Cytokinesis:– Cell divides to produce twohaploid cells with twoattached sister chromatidsDr. J MoghrabyAnaphase I Telophase I &Cytokinesis© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Meiosis IIEnter without going through interphase or replicatingDNASimilar to mitosis but with only half number ofchromosomeschromosomesDr. J Moghraby
    • Prophase II:– Spindle formation andcondensation of chromosomecondensation of chromosomeDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Metaphase II:– Sister chromatids arranged onmetaphase platesmetaphase plates– Kinetochores attach tomicrotubules extending fromopposite polesDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Anaphase I:– Sister chromatids separate, andmove towards opposite poles ofmove towards opposite poles ofthe cell– Due to crossing over, sisterchromatids are no longeridenticalDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Telophase II & Cytokinesis:– Nuclei form, cell divides toproduce two haploid cellsproduce two haploid cells– Cytokinesis separates thecytoplasm– Result is four haploid cellscontaining a single copy ofeach chromosomeDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
    • Number of viable gametes from meiosis differsIn males, meiosis results in four spermatids of similarsizeIn females, meiosis is asymmetric; only one oocyteIn females, meiosis is asymmetric; only one oocyteproducedDr. J Moghraby BIOL101
    • Meiotic Timelines for HumansDr. J Moghraby© 2001 Nature Publishing Group Hassold, T. & Hunt, P.
    • Meiotic DivisionMetaphase IProphase I Anaphase ITelophase I andCytokinesisDr. J MoghrabyProphase II Metaphase II Anaphase IITelophase II andCytokinesis
    • Comparison of Mitosis and Meiosis inDiploid CellsMITOSIS MEIOSISMEIOSIS IProphase IChiasmaChromosomereplicationHomologouschromosomepairChromosomereplication2n = 6Parent cellProphaseReplicated chromosomeDr. J MoghrabyMetaphase Metaphase IAnaphase ITelophase IHaploidn = 3Daughtercells ofmeiosis IMEIOSIS IIDaughter cells of meiosis IInnnn2n2nDaughter cellsof mitosisAnaphaseTelophase
    • SummaryCell cycle consists of interphase followed by M-phaseThree major checkpoints regulate cell cycleMitosis results in two genetically identical daughtercells from a single cellMeiosis results in four, haploid daughter cells that areDr. J Moghraby BIOL101Meiosis results in four, haploid daughter cells that aregenetically distinct