Objectives*for*Exa m *1*P C B*30 63 ,*Summer*2012 **!Mitosis*and*Meiosis*(Chapter*2)**!Q:!Of!basic!importance!in!this!material!is!to!know!the!essential!differences!between!mitosis!and!meiosis,!what!homologous!chromosomes!are!and!how!they!behave!in!mitosis!and!meiosis.!!!! Mitosis=!mitosis!produces!somatic!cells!(all!cells!except!for!reproductive!cells)!!* * =!!!*Mitosis!produces!2!genetically!identical!daughter!cells*! ! ! =!!!!Each!daughter!cell!gets!1!chromatid!from!chromosome!! ! ! =!!!!New!sister!chromatid!made!for!each!chromosome!! ! =!!!!Mitosis!does*not!change!the!number!of!chromosomes!!! Homologous*Chromosomes=!PAIR!DURING!MEIOSIS!= The!cell!division!that!occurs!as!apart!of!the!creation!of!gametes.!!= Sections!of!the!DNA!can!sometimes!cross!over!between!homologous!pairs!Meiosis=!produces!reproductive!cells!(sperm!and!egg)!= Formation!of!gametes!= One!diploid!cell!divides!twice!and!forms!4!haploid!cells!= Each!daughter!cell!gets!one!chromatid!from!each!pair!of!homologous!chromosomes!2n=4;*n=*2**Meiosis*I:*= First!division,!homologous!chromosomes!separate!into!different!daughter!cells.!= Crossing!over!occurs!(chromosome!recombination)!Meiosis*II:**= Second!division,!sister!chromatids!separate!in!to!different!daughter!cells!!In!MI!&!MII,!DNA!is!first!replicated!and!then!different!methods!are!used!for!separation!of!the!replicated!genetic!information.!Before!replication!chromosomes!exist!as!a!single!DNA!double!helix!bound!by!histone!proteins!(chromatin)!!2n!=!2!copies!of!each!chromosome!!2n!=!2!pairs!of!homologous!chromosomes!=!diploid!#!of!4!!! 2n!=!4!chromosomes!!!Q:!Understand!the!concept!of!the!cell!cycle!and!know!what!happens!during!S=phase.!!!G0=!cell!gets!ready!for!DNA!replication;!resting!phase.!(does!not!divide!in!this!phase)!Interphase!–!the!chromosomes!are!un=condensed;!cell!grows!the!proceeds!to!G1,!S,!and!G2!phases.!G1=!checkpoint!makes!sure!everything!is!ready!for!DNA!synthesis!(replication);!synthesis!of!enzymes!and!lots!of!growth.!S*(synthesis)=!chromosome!duplication!occurs;!this!phase!is!complete!when!each!chromosome!has!2!sister!chromatids!G2=!cell!is!preparing!structures!(like!microtubules)!necessary!for!mitosis;!check!point!makes!sure!the!cell!is!ready!to!enter!cell!division!phase,!M!phase.!!Q:!Be!able!to!name!the!stages!of!mitosis!and!know!what!events!take!place!in!each.!!!Mitosis=!cell!growth!stops!here;!division!into!2!daughter!cells!Prophase!–!chromatin!begins!to!condense!and!become!visible:!centrioles!start!moving!to!opposite!ends;!start!of!spindle!formation!(coil)!Metaphase*–!spindle!fibers!align!the!chromosomes!along!the!metaphase!plate!(align)!!Anaphase*–!the!paired!chromosomes!separate!at!the!kinetochore!(centromere)!and!move!to!opposite!sides!of!the!cell!(separate)!Telophase*–!new!membranes!form!around!daughter!cells;!chromosomes!uncondensed!(uncoil)!Cytokenisis*–!the!cells!completely!divide!into!two!daughter!cells.!(Plants,!cell!plate)!!Q:!Know!what!sister!chromatids!are.!!!! Sister*Chromatids*–are!exact!duplicates;!a!condensed!chromosome!ready!for!division!(mitosis).!Sisters!have!2!arms!!Q:!Understand!the!haploid!and!diploid,!and!know!what!homologous!chromosomes!are,!how!they!are!similar!to!each!other!and!how!they!differ!from!nonhomologous!chromosomes.!!!Haploid*–!(n)!the!number!of!chromosomes!in!a!gamete.! !Diploid*–!(2n)!the!number!of!chromosomes!in!a!somatic!cell.!!=Humans!are!diploid.!Humans!contain!46!chromosomes:!2!complete!haploid!sets,!which!make!up!23!homologous!chromosome!pairs!Homologous*Chromosomes*–!carry!the!same!genes!but!may!have!different!alleles;!have!same!centromere!position,!same!length.!NonShomologous*chromosomes*would!carry!completely!different!genes.!!!***Exception!=!sex!chromosomes,!which!are!homologous!chromosomes!but!don’t!carry!the!same!genes!!!Q:!Know!the!important!events!that!occur!in!meiosis!and!understand!how!meiosis!differs!from!mitosis.!!!! Meiosis*I*Prophase*1S*homologous!chromosomes!pair!up!and!form!synapses!(these!paired!chromosomes!are!called!bivalents!(tetrads))**Metaphase*1S*bivalents!line!up!along!the!metaphase!plate!!Anaphase*IS*chiasmata!separate;!chromosomes!(each!with!2!chromatids)!move!to!separate!poles.!=Each!of!the!daughter!cells!is!now!haploid!(23!chromosomes);!but!each!chromosome!has!2!chromatids.!Telophase*I*/*Cytokinesis*I*S*nuclear!envelopes!may!reform,!or!cell!may!go!right!into!meiosis!II;!2!complete!daughter!cells!form!!!! Meiosis*II**=In!metaphase!II,!the!chromatids!separate!and!become!independent!chromosomes.!=No!DNA!replication!before!meiosis!II!!!!!!=Everything!else!is!pretty!similar!to!Meiosis!I,!except!the!chromosome!number!is!not!reduced!!! !! Differences*between*mitosis*and*meiosis:*=!Chromosomes!in!meiosis!undergo!a!recombination!which!shuffles!the!genes.!!=!Crossing!over!==results!in!different!genetic!combinations!in!each!gamete.!!=!Outcome!of!meiosis!is!4!haploid!cells!(all!genetically!unique),!compared!with!the!two!(genetically!identical)!diploid!cells!produced!from!mitosis!!!=In!the!first!meiotic!division,!the!number!of!cells!is!doubled,!but!the!number!of!chromosomes!is!not==results!in!1/2!as!many!chromosomes!per!cell.!!=The!second!meiotic!division!is!like!mitosis;!the!number!of!chromosomes!does!not!get!reduced!!=At!the!end!of!division!1,!each!of!2!daughter!cells!has!2!chromosomes!(each!with!2!chromatids)!and!no!pairs.!=Second!division=!4!daughter!cells,!each!with!2!chromosomes!(each!of!these!chromosomes!only!have!1!chromatid)!!!!!Q:!Be!able!state!how!many!chromosomes!and!pairs!of!homologous!chromosomes!are!present!in!cells!of!a!given!diploid!number!that!are!undergoing!meiosis.!Understand!the!terms!tetrad,!chiasmata,!crossing!over!and!recombination.!!!TetradS*(bivalents)!paired!and!replicated!chromosomes;!2!chromosomes,!4!chromatids,!with!1!chromosome!coming!from!each!parent.!ChiasmaS*the!point!where!two!homologous,!non=sister!chromatids!exchange!!genetic!material!during!chromosomal!cross=over!during!meiosis!!Crossing*overS*exchange!of!genetic!material!between!homologous!chromosomes,!one!of!the!final!phases!of!recombination!!RecombinationS*a!process!in!which!a!molecule!of!DNA!is!broken!and!then!joined!to!a!different!one!!!***Skill!==!be!able!to!solve!genetics!problems!similar!to!those!suggested!as!homework!in!chapter!2!and!in!the!first!quiz.!!!Review*of*Mendel’s*Principles*(Chapter*3)**Q:!Be!able!to!state!Mendel's!postulates!(Random!Segregation!and!Independent!Assortment)!and!understand!their!significance.!!!Mendelʼs*Postulates:**1.
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