Pmed214 m&m 2012(1)

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Pmed214 m&m 2012(1)

  1. 1. Mitosis & MeiosisDr. Jeelan MoghrabyB.Sc., D.PhilAssistant ProfessorEmail: moghrabyj@ksau-hs.edu.saPMED214 2013
  2. 2. ObjectivesCell DivisionPhases of the cell cycleMitosisMeiosisDr. J MoghrabyMeiosis
  3. 3. Cell DivisionContinuity of life is based on the reproductionof cells
  4. 4. 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
  5. 5. 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
  6. 6. ChromosomesChromosomeduplication(including DNAsynthesis)Chromo-some armDNA moleculesResults in twoidentical copiescalled sisterchromatids that areDuplication of DNADr. J MoghrabySisterchromatidsSeparation ofsister chromatidsCentromereSister chromatidschromatids that areconnected bycentromeres
  7. 7. Phases of the Cell CycleDr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
  8. 8. 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
  9. 9. 2001 Nobel Prizes in Eukaryotic Cell CycleHartwell Nurse HuntDr. J MoghrabyHartwell Nurse HuntCell cycle checkpointsCyclin-dependent kinasesCyclins
  10. 10. 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
  11. 11. Mitotic & Meiotic Cell CyclesMitosisDr. J MoghrabyMeiosis© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.
  12. 12. 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
  13. 13. MitosisGeneration of two identical daughter cellsfrom a single cell
  14. 14. Mitosis is Divided into Five PhasesProphasePrometaphaseMetaphaseAnaphaseDr. J MoghrabyAnaphaseTelophaseCytokinesis begins during telophase
  15. 15. 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.
  16. 16. 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.
  17. 17. 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.
  18. 18. 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.
  19. 19. 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.
  20. 20. MITOTIC (M) PHASECytokinesisMitosisSG1G2Mitotic DivisionDr. J MoghrabyTelophase &CytokinesisAnaphaseMetaphasePrometaphaseProphase
  21. 21. MeiosisGeneration of four, genetically distinct,haploid cells from a single cell
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. Stages of MeiosisInterphaseHomologous pair of chromosomesin diploid parent cellDr. J MoghrabyChromosomesreplicateHomologous pair of replicated chromosomesSisterchromatids Diploid cell withreplicatedchromosomes
  26. 26. InterphaseHomologous pair of chromosomesin diploid parent cellChromosomesreplicateHomologous pair of replicated chromosomesDr. J MoghrabySisterchromatids Diploid cell withreplicatedchromosomesMeiosis IHomologouschromosomesseparate1Haploid cells withreplicated chromosomes
  27. 27. 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
  28. 28. Meiosis IProphase IMetaphase IAnaphase IMeiosis IIProphase IIMetaphase IIAnaphase IIAnaphase ITelophase I &cytokinesisAnaphase IITelophase II &cytokinesisDr. J Moghraby
  29. 29. 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.
  30. 30. 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.
  31. 31. 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.
  32. 32. Meiosis IIEnter without going through interphase or replicatingDNASimilar to mitosis but with only half number ofchromosomeschromosomesDr. J Moghraby
  33. 33. 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.
  34. 34. 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.
  35. 35. 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.
  36. 36. 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.
  37. 37. 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
  38. 38. Meiotic Timelines for HumansDr. J Moghraby© 2001 Nature Publishing Group Hassold, T. & Hunt, P.
  39. 39. Meiotic DivisionMetaphase IProphase I Anaphase ITelophase I andCytokinesisDr. J MoghrabyProphase II Metaphase II Anaphase IITelophase II andCytokinesis
  40. 40. 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
  41. 41. 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

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