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Reproduction:Not as simple as it looks.Reproduction presents a major problem for cells and organisms:(how can information be transmitted faithfully to progeny)IIIIIIIV=one bit ofgenetic information=one bit ofgenetic informationThe information transfer problem becomes more challenging as more bits of information are incorporated into the organismOne of lifes solutions to this challenge:“Package”the bits of information into single units called chromosomes=one bit ofgenetic informationchromosomesPackaging of genetic material in prokaryotes and eukaryotesprokaryote celleukaryote cellFig 2.4 The structure of a highly condensed,replicated chromosome.2019 John Wiley and Sons PublishersA ChromosomeBASIC GENETICSEach cell in the human body contains two sets of 23 chromosomes Mitosis identically replicates this informationEach cell therefore has the same genetic materialReproductive cells only have one set of chromosomes.These combine to make a new person with different genetic material to both parentsThe cell cycle.2019 John Wiley and Sons PublishersMitosisThe Stages of the Cell CycleM stageMitotic StageThe nucleus and cytoplasm split to make two new cellsknown as DIPLOID cellsEvery dividing tissue cell in the body is always at a stage of the cell cycle.Whether it is at:-STAGES OF MITOSISCytokinesisThus enabling the body to continuously make new body tissue for growth and repair.Diagram showing the Stages of MitosisProphaseMetaphaseAnaphaseTelophaseInterphaseProphaseMetaphaseAnaphaseTelophaseThe Stages of MitosisInterphaseThe Spindle A spindle is a web type structure made up of microtubule fibres.It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division.Mitotic centreMicrotubuleA cell at metaphasea spindleChromosomes attached to spindle during nuclear divisionINTERPHASEAfter a cell has divided,the two new cells begin the process again,the cells at this stage are in Interphase.Cell cycle It is divided into three mini stages:-G1 S G2Eukaryotic chromsome replicatingPROPHASEThe chromatin(unravelled DNA)in the nucleus,condenses to form pairs of chromosomes.The centrioles move to opposite ends of the nucleus.As this is happening the nucleolus begins to break down Nuclear membrane begins to break downProphaseChromatin condenses(remember that chromatin/DNA replicate during Interphase),the nuclear envelope dissolves,centrioles(if present)divide and migrate,the spindle forms.METAPHASEThe spindle becomes fully developed The nuclear membrane has completely gone The chromatid pairs place themselves onto individual fibres and are aligned along the centre of the spindleANAPHASEThe chromatid pairs are split into two (This is done by movement of the spindle fibres)The pairs then travel to opposite ends of the spindleThe halved chromatids are now called chromosomesTELOPHASETwo new nuclei are formed when the chromosomes reach the opposite poles of the cellThe nuclear membrane is formed-the nucleolus reappearsThe chromosomes disperse in the nucleusREMEMBER!InterphaseProphaseMetaphaseAnaphaseTelophase IPMATMitosis in animal cells.2019 John Wiley and Sons PublishersCYTOKINESIS Literally means,division of the cytoplasm Mitosis is the splitting of the nucleus.Cytokinesis is the splitting of cytoplasm It usually begins during ANAPHASEObserved with place contrast microscopy.The work of Shinya Inoue and Rudolf Oldenbourge.The Mitosis World Website.The work of Mr Paul Maddox.The Mitosis World website.Kangaroo epithelial kidney cell going through mitotic division.Mitosis and cell plate formation in a flattened endosperm cell of the African bloodlily Haementhus Katherininae.Cell Turnover-The speed of mitosisAlthough you may have seen a speeded up video of mitosis in action.One full cycle can vary between a couple of minutes to days.For example skin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away.Cells which make up organs such as the eye and the brain,need not multiply as often once they reach adult size.Click here for moviesOrgans which need to produce new cells continuously have the highest turnover.For example:-Bone marrow-producing replacement blood cells The testes-producing semenTumoursAbnormalities can sometimes occur in cells which reproduce at a rapid rate,this in turn may lead to the formation of tumours.Tumours of any type should be considered serious.Although benign tumours do not usually cause a threat to a persons life,they can cause great inconvenience if not treated.This powerpoint was kindly donated to worldofteachingworldofteaching is home to over a thousand powerpoints submitted by teachers.This is a completely free site and requires no registration.Please visit and I hope it will help in your teaching.谢谢！
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