Case study 2YizheWangHonorsBiologyJan.9th,20131.Recordthestagesofmeiosisineukaryoticcellsrealizingthattherearetwocelldivisionsinvolved,eachhavingtheirparticulartermsandcharacteristics.ThemeiosisineukaryoticcellsstartswithProphaseI,wherethereare23pairsofchromosomesinarow.T...
YizheWangHonorsBiologyJan.9th,20131.Recordthestagesofmeiosisineukaryoticcellsrealizingthattherearetwocelldivisionsinvolved,eachhavingtheirparticulartermsandcharacteristics.ThemeiosisineukaryoticcellsstartswithProphaseI,wherethereare23pairsofchromosomesinarow.Thechromosomesfromfatherarepairedupwithhismother’schromosomes,andeachchromosomeiscomposedoftwochromatids.TheninMetaphaseI,thechromosomesmovetothecenterofthecellandlineupwiththemother’sandthefather’ssidebyside.LaterinAnaphaseI,therearesomethreadsthatareformedinthecellthatattachtothechromosomes.Thesearethespindlefibersandtheyacttopullthesetsofchromosomesapart.Whenthefatherandmother’schromosomepairslietogetherthatdoesn’tmeanthattheylineupsothatallofthemother’sareononesideandthefather’sareontheother,theycouldbeoneitherside.InTelophaseI,twocellsareformedeachwithitsowncollectionof23chromosomes,anditisnotoverbecausethechromosomesstillhavetheirchromatids.InProphaseII,thenuclearmembranesstarttodissolveagain.TheninMetaphaseII,thechromosomesareliningupinthemiddleofthecellandthespindlefibersattachtotheirchromatids.LaterinAnaphaseII,thefiberspullchromatidsapart.InTelophaseII,thecellsdivideagainandmakefourcellsintotal.2.Listthekeydifferencesbetweenmitosisandmeiosis.Inmeiosis,cellsdividetwice,andinmitosis,cellsdivideonlyonce.Aftermeiosis,4daughtercellsareproducedwhilethereareonly2formitosis.Thetypeofreproductionformeiosisissexualwhileitisasexualformitosis.Duringmeiosis,crossingovercanoccurwhileitcannotduringmitosis.3.Doprokaryoteshaveeithermitosisormeiosis?Prokaryotesdonothaveeithermitosisormeiosis.Duetotheirlackofnucleus,andeachoneofthemonlyhaveoneDNAmolecule,itcanonlyhavebinaryfission.4.Crossoveroccursbetweenhomologouspairsofchromosomes,butcanitoccurbetweentwodifferentchromosomes;saybetween#1and#7?No,itcannotoccurbetweentwodifferentchromosomes.Becausecrossingoverrearrangesgeneticinformation,and#1and#7donothavethesamegene.Therefore,crossoverwillnotoccursbetweendifferentchromosomes.5.Wasitanevolutionarynecessitythatmeiosisevolvedatthesametimeassexualreproduction?No,itwasnot.Inordertoseethesexualreproduction,themeiosisshouldtakeplacebeforethesexualreproductionhappens.
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