Cell Division

Name: __________________ Topic: Cell Division Relationship between reproduction, mitosis and meiosis LO: State the importance of mitosis in growth, repair and asexual reproduction ● Forgrowthof an organism by producing new cells● Forrepairof worn-out parts of body● Forasexual reproductiono Example: Storage organs in plants can develop roots and shoots by mitosis. LO: Explain the need for the production of genetically identical cells● To ensure all the genes arecorrectly copiedandpasseddown to future offspring.● To producegenetically stabledaughter cells whichcontain all the genes needed forsubsequent cell division and differentiation.● To preventuncontrolled cell division. Concepts Summary NotesNan Hua High School Biology 1

Name: __________________ Topic: Cell Division LO: Identify, with the aid of diagrams, the main stages of mitosis Cell cycle Stages of cellcycle:1. Interphase(DNAreplication)2. Mitosis/Meiosis(PMAT)3. Cytokinesis(Cleavageofcytoplasm) Stages of mitosisProphase -Chromatin threadscondense, coil and shortento formchromosomes,spindle fibre formsandnucleolus and nuclear membranedisappearsMetaphase -Chromosomes line upsingly along the equatorof the cellattached to thespindle fibre at the centromereAnaphase -Centromeres splitandsister chromatidsseparateto form daughterchromosomes which are pulled to opposite poles of the cellTelophase-Nuclear envelop and nucleolus reforms,spindle fibre disintegrate,chromosomes uncoil back to chromatin threadsandcleavagefurrow forms, followed bythe division of cytoplasm (cytokinesis). Concepts Summary NotesNan Hua High School Biology 2

Name: __________________ Topic: Cell Division LO: State what is meant by homologous pairs of chromosomes ● Homologouschromosomes arechromosomes, which existin pairs(one maternal andone paternal) and eachpair has thesame shape,size, length, position ofcentromere and sequenceof genes / gene loci.● One is inheritedfrom the male parent andthe other is inherited fromthe female parent. Hence,theycanhavedifferentalleles. Concepts Summary NotesNan Hua High School Biology 3

Name: __________________ Topic: Cell Division LO: Identify, with the aid of diagrams, the main stages of meiosis (names of thesub-divisions of prophase are not required) Concepts Summary NotesNan Hua High School Biology 4

Name: __________________ Topic: Cell Division Stages of meiosis Meiosis I: Prophase I -Chromatin threadscondense, coil andshortento formchromosomes,spindle fibre formsandnucleolus and nuclear membranedisappearsHomologous chromosomes pair up (synapsis).Crossingover may occurbetweenhomologous chromosomes, resulting innew combinationsof alleles. Point at which theycross over is called thechiasma.Metaphase I-Homologous chromosomesline upin pairsalong the equatorof the cellattached to the spindle fibre at the centromere. Concepts Summary NotesNan Hua High School Biology 5

Name: __________________ Topic: Cell Division Independent assortmentoccurs wherepairs of homologous chromosomes line uprandomlyalong the equator, resulting innew combinationsof chromosomes.Anaphase I –Homologous chromosomes separateandeachchromosome is pulled toopposite poles of the cellTelophaseI -Nuclear envelop and nucleolus reforms, spindle fibre disintegrate,chromosomes uncoil back to chromatin threadsandcleavagefurrow forms, followed bythe division of cytoplasm (cytokinesis I).Meiosis II:Prophase II -Chromatin threadscondense, coil andshortento formchromosomes,spindle fibre formsandnucleolus and nuclear membranedisappearsMetaphase II -Chromosomes line upsingly along theequatorof the cellattached to thespindle fibre at the centromereAnaphase II -Centromeres splitandsister chromatidsseparateto form daughterchromosomes which are pulled to opposite poles of the cellTelophaseII-Nuclear envelop and nucleolus reforms,spindle fibre disintegrate,chromosomes uncoil back to chromatin threadsandcleavagefurrow forms, followed bythe division of cytoplasm (cytokinesis II),producing4 haploid daughter cells. Stage Number of chromosomes Amount of DNAStart of interphase 2n (diploid) 2n End of interphase 2n (diploid) 4n (doubled due to DNAreplication)End of meiosis I n (haploid) 2n End of meiosis II n (haploid) n Differences between mitosis and meiosis Concepts Summary NotesNan Hua High School Biology 6

Name: __________________ Topic: Cell Division Concepts Summary NotesNan Hua High School Biology 7

Name: __________________ Topic: Cell Division LO: Define the terms haploid and diploid, and explain the need for a reductiondivision process prior to fertilisation in sexual reproduction ● Haploidisaconditionofcellsthatcontainhalfthenumberofchromosomes,nofthe parent cell.● Diploidisaconditionofcellsthatcontainthefullnumberofchromosomes,2nasin the normal body cell.● Reductiondivisionis a typeof celldivisionthatproducescellswithhaploidnumber of chromosomes. Need for a reduction division process prior to fertilization:● Fertilisationis thefusionof thenucleusof thehaploidmalegametewiththenucleusof thehaploidfemalegamete, to forma diploidzygote, restoringthediploid number of chromosomesin the species.LO: State how meiosis and fertilisation can lead to variation● Genetic variations due to meiosis:o Crossing overduringProphase Ileads tonew combinationsof alleles.o Independent assortment of chromosomesduringMetaphaseI results in newcombination of chromosomes. ● Fertilisation of male gamete and female gamete is also arandom process,whichcan result ingenetic variation in the offspringasthegametes produced by meiosisare genetically different. Concepts Summary NotesNan Hua High School Biology 8